Thermally activated delayed fluorescent conducting organic polymers for OLED application

1 Introduction

Thermally activated delayed fluorescence (TADF) materials have revolutionized the development of organic light-emitting diodes (OLEDs) due to their ability to harvest triplet excitons (Figure 1), a process tradition ally considered non-radiative, without relying on costly precious metals (Saravanan et al., 2025). In recent years, TADF-based macromolecules, polymers, and dendrimers have emerged as promising materials for solution-processed OLED technologies, particularly for fabrication methods such as spin coating and inkjet printing (Figure 2). In this review highlights recent progress in TADF-based macromolecules, polymers, and dendrimers designed specifically for solution-processed OLED fabrication techniques such as spin coating and inkjet printing (Ravikumar and Dangate, 2024a). Among these materials, TADF emitters have emerged as a particularly promising class of emitters for developing high-performance solution-processed OLEDs (SP-OLEDs) (Zhou et al., 2022). Polymers have already been widely explored as emitters in both phosphorescent and fluorescent solution-processed systems. Compared to small-molecule OLEDs fabricated through thermal vacuum deposition, solution-processed OLEDs offer a major advantage in terms of reduced energy consumption and lower manufacturing costs, making them attractive for large-scale and cost-effective production. Moreover, polymers offer great flexibility in molecular design, as various optoelectronic functional units such as emitters, hosts, spacers, solubilizing groups, and charge-transporting moieties can be incorporated directly into the polymer backbone or attached as side chains. Precise control over the polymerization process allows the ratios of these functional units to be finely tuned, which helps prevent phase separation within the material and enables the polymer to be used as a single, well-integrated emissive layer (EML) (Ravikumar et al., 2024). In addition, polymeric materials generally exhibit excellent film-forming properties, often outperforming low-molecular-weight materials in solution-processed OLED applications (Manimaran and Shrinivas Dangate, 2025).

TADF polymers can be designed through several strategies, most commonly by integrating donor (D) and acceptor (A) units within the material (Ravikumar and Dangate, 2025a). The way these subunits are arranged plays a crucial role in determining their interaction and overall photophysical behaviour. One approach involves constructing the polymer backbone from repeating donor units, with acceptor groups attached as pendant side chains to create D-A emissive sites. In another strategy, a well-established D-A type TADF emitter is grafted onto a non-conjugated or weakly conjugated polymer backbone, where it functions as a pendant functional unit (Ravikumar and Dangate, 2024b). A third design involves alternating donor and acceptor units directly along the main polymer chain, enabling controlled electronic communication between them. A fourth strategy involves positioning donor and acceptor groups as separate pendant units on a non-conjugated polymer backbone, allowing thermally activated delayed fluorescence (TADF) to arise through through-space charge transfer interactions. To achieve proper charge balance and effective triplet exciton confinement, additional functional groups can be incorporated either as pendant units or directly into the polymer chain, where they function as host materials or non-conjugated spacers. Although the strategies discussed here are among the most frequently reported and are therefore emphasized in this section, the list of materials summarized in Tables 1–4 is not exhaustive. The highly versatile combinations of donor-acceptor (D-A) TADF emitters, together with the extensive scope and sophistication of modern polymer chemistry, provide virtually limitless opportunities for innovation in this field (Pander et al., 2018; Ravikumar and Dangate, 2025b; Ravikumar and Dangate, 2026).

TABLE 1. Outline of pendant type polymer TADF emitter photophysical and device performance.

TABLE 2. Outline of acceptor pendants donor backbone TADF polymer’s photophysical and device performance.

TABLE 3. Outline of main-chain donor-acceptor TADF polymer’s photophysical and device performance.

TABLE 4. Outline of through-space charge transferred (TSCT) TADF polymer’s photophysical and device performance.

Efficient TADF hinges entirely on narrowing the singlet-triplet energy splitting (Δ_EST). Doing so minimizes the thermal activation barrier needed to kick off the RISC process. To hit this target, typical molecular designs rely on donor-acceptor (D-A) frameworks featuring highly twisted geometries. This intentional twisting forces spatial segregation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Consequently, the electron exchanges integral drops, effectively shrinking Δ_EST. The catch, however, is that pulling the HOMO and LUMO too far apart amplifies the charge-transfer (CT) nature of the excited state. This dampens the oscillator strength, stalls radiative decay rates, and ultimately compromises photoluminescence quantum yields. Balancing strong charge transfer against adequate orbital overlap is therefore a persistent tightrope in molecular engineering (Li and Leo, 2026).

When working with longer wavelength emissions like orange, red, or near-infrared (NIR) TADF systems designers run directly into the Energy Gap Law (EGL). Under the EGL, non-radiative decay rates (k _nr) scale up exponentially as the energy gap separating the excited state from the ground state closes. Because of this math, longer-wavelength emitters lose a massive chunk of their energy to non-radiative dissipation during the S₁→S₀ transition. To fight this loss, current strategies focus on rigidifying highly conjugated molecular skeletons and pairing them with aggressive electron-withdrawing segments. Cyano-substituents, fused heteroaromatic cores, and aromatic ketones are prime examples. These rugged structural changes stabilize the CT state, clamp down on vibrational relaxation, and rescue overall TADF efficiencies (Salerno et al., 2026). Lately, shifting focus toward donor engineering has yielded excellent results for high-performance systems. Tying donor units together with heteroatom bridges is particularly effective. This trick ramps up electron-donating power, stiffens the molecular spine, and locks down the D-A dihedral angle. Tweaks like this successfully squeeze Δ_EST without destroying the electronic coupling necessary for fast spin transitions. Ultimately, smart structural choices dictate everything from faster RISC rates to sharper emission bands and target colour coordinates (Saravanan et al., 2025; Salerno et al., 2026).

On the theoretical front, density functional theory (DFT) and its time-dependent variant (TD-DFT) have become indispensable for mapping out electronic behaviour ahead of time. Calculating HOMO-LUMO distributions, singlet-triplet gaps, oscillator strengths, spin-orbit coupling, and vertical excitation energies gives a clear picture of how a molecule will behave before setting foot in the wet lab. In practice, TD-DFT predictions match up nicely with real-world photoluminescence (PL) peaks, making quantum mechanical modelling a reliable screening filter for candidate OLED materials (Mariyappan and Gnanasekaran, 2025).

This review outlines recent progress in the molecular design of TADF macromolecules, polymers, and dendrimers developed for solution-processed OLEDs. We focus on how different structural frameworks specifically pendant systems, main-chain alternating donor-acceptor networks, and through-space charge transfer complexes dictate frontier orbital overlap, reverse intersystem crossing rates (k _*RISC*), and final external quantum efficiencies. Systematizing these diverse architectures is essential as OLED research shifts from laboratory fabrication toward scalable industrial techniques like inkjet printing. By analysing how polymer topology regulates charge transport, improves solvent resistance, and minimizes triplet-triplet annihilation, this work provides key design rules to help close the performance gap between solution-processable polymers and vacuum-evaporated small molecules.

To evaluate the true potential of polymer emitters, their performance parameters must be critically benchmarked against state-of-the-art vacuum-deposited small-molecule systems. Currently, small-molecule TADF systems reliably achieve outstanding device performance, with maximum external quantum efficiencies (EQE_max) exceeding 30% and exceptionally narrow emission bands (full width at half maximum), FWHM ≈20–30 nm. In contrast, the majority of TADF polymers reported to date hover around an EQE_max of 10%–20% with considerably broader emission spectra (FWHM ≈50–80 nm). To close this performance gap, specific magnitudes of improvement are required: a 1.5-fold–2-fold increase in efficiency (targeting >25%), a 20–30 nm reduction in FWHM to ensure deep colour purity, and a substantial optimization of charge balance by counteracting the typically sluggish electron mobility relative to hole transport in organic polymer matrices. For large-area displays and flexible electronics, a ‘manufacturing compromise’ is entirely justifiable; an intermediate EQE of 15%–20% paired with a moderate FWHM of ∼50 nm is highly acceptable and commercially viable if it allows for low-cost, high-throughput solution processing, which eliminates the massive capital expenditures associated with high-vacuum deposition systems.

2 Fundamental concepts, molecular engineering, and analytical evaluation

2.1 TADF emitters

The working mechanism behind thermally activated delayed fluorescence harvest both singlet (25%) plus triplet (75%) excitons during electrical excitation. Such action drives internal quantum efficiency levels near 100%. Exciton up conversion from the lowest triplet state to the lowest singlet state happens via reverse intersystem crossing paths. The rate of this process follows the Arrhenius equation and stays inversely proportional to energy differences between singlet and triplet states. Energy difference equations denote this value as being approximately twice the exchange integral found between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Reducing energy splitting requires spatial separation between those specific molecular orbitals. Polymeric designs achieve this separation using twisted donor and acceptor components inside polymer chains. Placement of these subunits occurs along the backbone or through dangling groups. Spatial interactions ensure effective charge transfer transitions during light emission cycles. Scientists strive for efficiency by carefully balancing these internal components (Rajapriya and Dangate, 2024; Diesing et al., 2026; Tang et al., 2026).

2.2 Common device layout and construction steps

Distinct from small-molecule emitters needing high-vacuum thermal evaporation, TADF polymers offer scalability through liquid phase processing. Standard organic light emitting diode architectures contain layers including an anode, hole injection layers, hole transport materials, the emissive layer, electron transport zones, and final cathode structures. Scientists create these devices using wet techniques like spin coating, inkjet deposition, or slot-die printing methods. Multi-layer processing poses one major hurdle involving layer solubility during wet film deposition. Chemical solvents during the application phase risk washing away lower films. Solutions involve using orthogonal solvents for distinct layers. Dissolving emission polymers within nonpolar toluene works when combining these alongside alcohol soluble layers elsewhere. Another approach focuses on creating polymers possessing thermally cross linkable groups. Such additions stop solvent interference after material curing finishes inside thin films. These steps ensure sharp device interfaces necessary for diode functions across massive substrate areas. Evaluation of TADF polymer quality focuses on three optoelectronic performance indicators. External quantum efficiency measures the ratio between emitted photons and total injected electrons. Maintaining high performance requires optimal photoluminescence yields along with balanced charge carrier injection pathways. Efficiency roll-off describes quantum efficiency losses seen when current density rises. Polymer systems battle these drops using triplet harvesting suppression techniques. Rigid structures plus sterically hindered pendants isolate triplets effectively within molecular voids (Suneesh et al., 2025). Commission Internationale de l'Eclairage coordinates track colour perceptions upon a standard grid. Displays require saturated colours matching Rec.2020 blue standards for global commercial adoption. Because these polymers hold structurally flexible excited states, spectral profiles often span broad wavelengths. Large width values shift coordinate readings toward washed-out regions inside the visible spectrum space. Scientists target narrower band emissions to fix colour fidelity issues within upcoming light sources. Advancements in structural control yield higher saturation levels. Continued progress shapes future display reliability during extreme high-speed performance tasks while minimizing thermal dissipation loads. Researchers strive for perfect light generation through refined design tactics focusing upon molecular orientation and orbital coupling strategies throughout material production lines for better visual display fidelity outputs today, ensuring stable colours. Restricting conformational freedom through precise macromolecular engineering is essential to narrow the FWHM and achieve high colour purity (Salah et al., 2026; Cole et al., 2022).

2.3 Industrial and technology impact

The efficient TADF conducting polymers have the potential to bridge the sophisticated chemical synthesis and the display and lighting applications. The TADF materials have the advantage of not using the expensive and scarce noble metals, such as Iridium or Platinum, which are commonly used in the phosphorescent OLEDs. As a result, the material cost can be significantly reduced. Furthermore, the solution-processable TADF conducting polymers can be used to fabricate the flexible displays, wearable electronics and large-area solid-state lighting panels in a high-throughput roll-to-roll fashion, which greatly reduces the production cost and overhead (Ravikumar and Dangate, 2024a).

3 TADF emitters polymers with pendant

One of the simplest and most effective strategies for designing TADF polymers is to attach well-established small-molecule TADF emitters to the polymer backbone as pendant groups. The resulting materials can be synthesized either by polymerizing monomers that already contain the TADF unit or by post-functionalizing a pre-formed polymer backbone. Depending on the design, the main chain may be optoelectronic active or electronically inert. For example, Xie et al. reported a series of efficient bluish-green polymers (PCzDP-x) by grafting the TADF emitter PXZ-DP-Cz onto a polycarbazole backbone (Figure 3). (Xie et al., 2017) In this system, the polycarbazole backbone not only promotes charge transport compared to aliphatic chains but also serves as an effective host material due to its high triplet energy (T₁) level. This high T₁ value helps prevent quenching of triplet excitons generated by the TADF emitter units, thereby enhancing device performance. Furthermore, in this “self-hosting” non-doped polymer system, the pendant TADF emitters are electronically isolated, which helps suppress aggregation-caused quenching (ACQ). This is achieved by incorporating N-ethylhexylcarbazole or N-hexylcarbazole-substituted monomers into the polymer backbone, effectively spacing and isolating the emissive units.

Among the series, polymer PCzDP-10, containing a 10 mol% fraction of TADF-functionalized monomers, exhibited the highest delayed emission contribution, accounting for 72% of the total emission, with a delayed lifetime (τ_e) of 2 μs. These polymers demonstrate strong potential for solution-processed OLED (SP-OLED) applications, as evidenced by their high photoluminescence quantum yields (Φ_PL) of 67% in toluene solution and 74% in the neat film. When PCzDP-10 was blended with mCP in a 1:1 ratio, the maximum external quantum efficiency (EQE_max) of the non-doped solution-processed OLED increased significantly from 2.8% to 5.9%. An even more remarkable improvement was achieved by incorporating an additional small-molecule TADF emitter, DMAC-DP-Cz, as a sensitizer. Under these conditions, the device delivered a substantially higher EQE_max of 16.1% at a luminance of approximately 100 cd·m^-2 (Table 1), while maintaining stable CIE coordinates around (0.24, 0.40) (Ravikumar and Dangate, 2024a).

Using a similar design strategy, the same group developed a multiple resonance (MR)-TADF polymer by grafting a green MR-TADF emitter (BN) onto a polycarbazole backbone as a pendant unit. The resulting polymers had molecular weights ranging from 4.4 to 10.0 kDa and polydispersity indices (PDI) between 1.40 and 1.87. Among the series, PCzBN1 and PCzBN3-containing 1% and 3% emitter-functionalized monomers, respectively-exhibited the best performance in doped solution-processed OLEDs (with 60 wt% polymer in mCP), achieving maximum external quantum efficiencies (EQE_max) of 17.8% and 17.3%, respectively (Table 1). In contrast, the device based on PCzBN5, which incorporated 5% emitter monomers, showed a reduced EQE_max of 13.3%. This decline in efficiency was attributed to increased aggregation-caused quenching (ACQ), resulting from the lower proportion of alkyl-carbazole monomers that normally act to spatially separate the emissive units and enhance solubility. The SP-OLEDs based on PCzBN1, PCzBN3, and PCzBN5 exhibited CIE coordinates of (0.10, 0.43) (0.12, 0.54), and (0.11, 0.53), respectively. For comparison, when BN was used as the standalone emitter, the SP-OLED achieved a maximum external quantum efficiency (EQE_max) of 16.3%. In contrast, the polymer-based devices incorporating PCzBN1 and PCzBN3 delivered improved EQE_max values of 17.8% and 17.3%, respectively. This enhancement in device performance is attributed to the superior solubility and improved film-forming properties of the polymer systems compared to the small-molecule BN emitter, while maintaining similar emission colour and TADF characteristics. Furthermore, the polymer-based OLEDs retained the intrinsic advantage of MR-TADF emitters, exhibiting narrowband emission with a full width at half maximum (FWHM) of approximately 30 nm across all fabricated devices (Wang et al., 2022).

Zong et al. adopted a similar molecular design strategy by grafting both host and TADF units as pendant groups onto a polycarbazole backbone to suppress aggregation-caused quenching (ACQ) (Zong et al., 2022). In this approach, “self-hosted” TADF polymers were synthesized using a modified mCP monomer (Figure 3) in combination with the small-molecule TADF emitter PXZ-TRZ. The resulting polymers exhibited molecular weights in the range of 7.5–8.0 kDa and polydispersity indices (PDI) between 1.5 and 1.6. A series of polymers, PCz-mCP-PXzTrz-x, containing varying emitter loadings (x = 10–40%), was prepared. Among them, PCz-mCP-PXzTrz-30 (30% emitter content) showed the highest photoluminescence quantum yield (Φ_PL) of 39% in thin film (measured in air), with an emission maximum (λ_PL) at 540 nm. The corresponding non-doped solution-processed OLED exhibited CIE coordinates of (0.35, 0.53) and achieved a maximum external quantum efficiency (EQE_max) of 15.3% (Tanaka et al., 2012; Rangasamy et al., 2026).

To regulate the conjugation length and enhance the triplet energy of the polymer backbone an aspect that is especially important for blue-emitting conjugated polymers such as polyfluorene- Yang et al. (2018a) introduced a 3,3′-dimethyldiphenyl ether unit into the backbone. As the proportion of the non-conjugated ether segment increased, the triplet energy of the polymer backbone rose from 2.16 eV for PFDMPE-R01 to 2.58 eV for PFDMPE-R10 (Figure 4). The synthesized polymers exhibited molecular weights in the range of 83–132 kDa and polydispersity indices (PDI) between 1.6 and 1.8. A red TADF emitter, ROC8 (Yang et al., 2018a), was grafted onto the polymer backbone as a pendant unit, enabling efficient energy transfer from the backbone to the emissive site. As a result, all polymers displayed red emission similar to that of the parent ROC8 emitter. With increasing ether content, the photoluminescence quantum yield (Φ_PL) of the thin films improved significantly, rising from 18% to 55%. Among the series, the device based on PFDMPE-R05 (Figure 4), containing 5 mol% of emitter-functionalized monomers, exhibited the best performance, achieving a maximum external quantum efficiency (EQE_max) of 5.6% at an electroluminescence peak (λ_EL) of 606 nm. The relatively long delayed lifetime (τ_d) of 126 μs was identified as the main reason for the pronounced efficiency roll-off, with the device efficiency decreasing by 82% at a luminance of 500 cd·m^-2. The extended τ_d promotes triplet-triplet annihilation and other triplet-related quenching processes at higher brightness levels, thereby limiting device performance. In a related study, Ban et al. (2022) developed a TADF polymer by incorporating modified 4CzCN units into a non-conjugated alkyl backbone, resulting in a material with a molecular weight of 7.5 kDa and a polydispersity index (PDI) of 1.5. The bulky 4CzCN moieties exhibited aggregation-induced emission (AIE) characteristics, contributing to a thin-film photoluminescence quantum yield (Φ_PL) of 37% for the polymer P-4CzCN (Figure 4), with an emission maximum (λ_PL) at 472 nm and a delayed lifetime (τ_d) of 1.5 μs. However, the corresponding non-doped solution-processed OLED showed a relatively modest maximum external quantum efficiency (EQE_max) of 3.6%, with CIE coordinates of (0.23, 0.39). In contrast, stronger encapsulation of the TADF core within self-hosting monomers led to a significant improvement in the neat-film photoluminescence quantum yield (Φ_PL). When non-conjugated alkyl-carbazole units were attached to the emitter in a semi-dendritic architecture (P-Cz4CzCN, Figure 4), the ΦPL increased substantially to 65% at an emission maximum (λ_PL) of 489 nm (Table 1).

Correspondingly, the maximum external quantum efficiency (EQE_max) of the doped solution-processed OLEDs improved markedly to 11.5%, with CIE coordinates of (0.24, 0.47), indicating minimal change in emission colour. Moreover, films of the encapsulated dendrimer-like TADF polymer exhibited significantly enhanced resistance to orthogonal solvents. This improved solvent tolerance not only helps reduce aggregation-caused quenching (ACQ) between emissive units but also facilitates the fabrication of fully solution-processed OLEDs, as subsequent layers above the emissive layer (EML) can be deposited from solution without damaging the underlying film. Li et al. (2022) reported a related strategy based on an asymmetric dendritic TADF unit (DMAC-DPS-Cz) that was terminally attached to a non-conjugated polymer backbone decorated with carbazole groups. The resulting polymer, PDCDC (Figure 4), exhibited a molecular weight of 12.7 k_DA and a narrow polydispersity index (PDI) of 1.16. In neat films, PDCDC showed greenish-blue emission at 496 nm with a high photoluminescence quantum yield (Φ_PL) of 68% (Table 1). The corresponding non-doped solution-processed OLED achieved a maximum external quantum efficiency (EQE_max) of 9.0%, with CIE coordinates of (0.23, 0.39). Comparison with earlier systems highlights the importance of carefully controlling the overall carbazole content to obtain highly emissive TADF polymer films. This can be achieved either by blending the polymer with an appropriate host material or by incorporating host units, such as mCP, directly into the polymer backbone through copolymerization.

Polyolefin has also been explored as a non-conjugated backbone for TADF polymers. Li et al. (2018) synthesized a series of TADF copolymers, PCzPT-x and POPT-x, using a monomer containing the emitter DBTO2-PTZ. In these systems, either hole-transporting carbazole units (PCzPT-x) or electron-transporting phosphine oxide spacer units (POPT-x) were incorporated as comonomers to tune the charge-transport properties. The resulting copolymers exhibited photoluminescence quantum yields (Φ_PL) of up to 36% and relatively small singlet-triplet energy gaps (ΔE_ST) in the range of 0.05–0.13 eV. Among the series, POPT-25 and PCzPT-19-where the number denotes the mol% of emitter-containing monomer (Figure 4)-showed the best performance within their respective families. These polymers possessed molecular weights of 27 and 16 kDa, with polydispersity indices (PDI) of 1.5 and 1.8, respectively. Notably, in POPT-25, the phosphine oxide pendant group was designed to function similarly to DPEPO, a widely used polar host material, thereby enhancing electron-transport and exciton confinement within the device. POPT-25 exhibited a relatively high photoluminescence quantum yield (Φ_PL) of 52% in toluene, whereas the control polymer PCzPT-19, which contained only donor-type pendant groups, showed a significantly lower Φ_PL of 25% (Table 1). Although both polymers incorporated the same pendant TADF emitter, their reverse intersystem crossing rate constants (k_RISC) differed markedly, with values of 1.9 × 10⁵ s^-1 for PCzPT-19 and 8.1 × 10⁵ s^-1 for POPT-25. This substantial difference highlights the strong influence of host pendant polarity on TADF kinetics. A yellow-emitting solution-processed OLED based on POPT-25 (10 wt% in mCP) achieved a maximum external quantum efficiency (EQE_max) of 5.2%, with CIE coordinates of (0.36, 0.50). In comparison, devices fabricated using 10 wt% doped mCP films showed that the improved charge balance and higher Φ_PL of POPT-25 (36% vs. 21%) led to superior device performance, whereas the SP-OLED based on PCzPT-19 exhibited a much lower EQE_max of 1.2%.

Additionally, Li et al. (2017), created polymers P1, P2, and P3 (Figure 4) based on the same emitter DBTO2-PTZ, here employing dibenzothiophene as the host monomer in place of carbazole. The molecular weights of polymers P1, P2, and P3 were 12, 30, and 23 kDa, respectively, and their PDIs were 1.3, 1.7, and 1.7, as well as their Φ_PL in neat films of 10.4%, 23.5%, and 19.5%. According to the Φ_PL sequence, the optimal environment for the TADF pendant group is provided by the monomer ratio in P2, which is almost equal in the TADF emitter and host monomers. When employing the co-monomer based on carbazole and dibenzothiophene, the SP-OLEDs with P2 likewise performed extremely similarly to its carbazole-based equivalent PCzPT-19, suggesting only minor variations in the hosting environment.

Li et al. (2019) further applied this design strategy to develop a series of blue TADF polymers, PDT-x. These materials incorporated the high-performance blue TADF emitter DMA-TXO₂ (Dos Santos et al., 2016) along with 9,9-dimethyl-10-phenylacridine (BDMAc), which possesses a high triplet energy (E_T = 3.38 eV), serving as both a host and spacer unit within the polymer structure. The molecular weights of PDT-1, PDT-2, and PDT-3 were 10, 11, and 21 kDa, respectively, with corresponding polydispersity indices (PDI) of 1.4, 1.7, and 1.7. In neat films, the photoluminescence quantum yields (Φ_PL) decreased to 42%, 54%, and 46% for PDT-1, PDT-2, and PDT-3, respectively (Table 1). These values are notably lower than that of the parent emitter, which exhibits a Φ_PL of 80% when doped at 11 wt% in DPEPO. The reduced Φ_PL in the polymer films is most likely attributed to concentration quenching, despite the presence of excess BDMAc spacer units intended to spatially separate the emissive sites.

The best-performing solution-processed OLED based on pristine PDT-2 achieved a maximum external quantum efficiency (EQE_max) of 5.3% at an electroluminescence peak (λ_EL) of 436 nm, with CIE coordinates of (0.15, 0.09). In comparison, a vacuum-deposited device based on the small-molecule emitter DMA-TXO₂ reached a significantly higher EQE_max of nearly 20%, highlighting the performance gap that still exists between polymer-based and evaporated small-molecule systems. Polynorbornene has also been explored as a backbone for TADF polymers. Owing to its relatively high triplet energy (E_T ≈ 2.95 eV), this backbone is well suited for blue TADF systems, as it effectively prevents triplet exciton quenching from the emissive units to the polymer chain. Zeng et al. (2018) reported a series of blue TADF polymers in which DMAC-DPS derivatives were incorporated as emissive monomers onto a norbornene backbone, while carbazole-containing monomers were introduced as hole-transporting units (Figure 4).

This design strategy was adopted to suppress undesired red shifting by preventing conjugation along the polymer backbone, thereby preserving the intrinsic photophysical properties of the TADF monomer units. In addition, the ring-opening metathesis polymerization (ROMP) technique enabled precise control over the molecular weight and structural uniformity of the resulting polymers. A series of polymers, PBD-0, PBD-5, PBD-10, PBD-15, and PBD-20, was synthesized by varying the molar fraction of the TADF monomer, yielding materials with molecular weights in the range of 5.8–8.0 kDa. All neat polymer films exhibited blue emission centered around 460 nm. Among them, the non-doped solution-processed OLED based on PBD-10 achieved the best performance, with a maximum external quantum efficiency (EQE_max) of 7.3% and CIE coordinates of (0.20, 0.29). The corresponding EQE_max values for devices based on PBD-5, PBD-15, and PBD-20 were 6.0%, 7.1%, and 6.7%, respectively, closely following the trends observed in their photoluminescence quantum yields (Φ_PL). The relatively slow reverse intersystem crossing rates (k _RISC) were associated with pronounced efficiency roll-off, with the EQE at 100 cd·m^-2 (EQE_max) decreasing by 45%–53%. Cole et al. (2022) developed the polymer D3P-DEH, which features three distinct side chains grafted onto a non-conjugated alkyl backbone (Figure 4). One side chain contains a TADF emitter as the emissive unit, while the other two incorporate charge-transporting functionalities. Specifically, a modified mCP unit (NmCP1) is introduced to function as an electron-transporting host material, alongside a hole-transporting component derived from mCP. Because both electron-and hole-transporting units are integrated directly into the polymer structure, an additional external host material is not required, enabling the fabrication of fully self-hosted emissive layers. To support this claim, the authors compared the performance of doped and non-doped devices. Although the overall efficiencies were relatively low, the non-doped device achieved a higher maximum external quantum efficiency (EQE_max) of 1.6% at CIE coordinates of (0.27, 0.50), outperforming the doped device (30 wt% in 26DCzPPy), which exhibited an EQE_max of only 0.6% (Table 1). Notably, this study also reported the first example of a “self-hosted” TADF polymer-based solution-processed OLED fabricated via inkjet printing, highlighting the potential of such materials for scalable and patternable device manufacturing.

4 Acceptor pendants donor backbone as a TADF polymer

Zhu et al. (2016) reported a TADF polymer named PAPTC, designed with a donor-type backbone and acceptor units attached as side groups. In this structure, acridan and carbazole moieties are linked through their 3-and 6-positions to build the conjugated main chain. The carbazole units serve a dual purpose: they help maintain sufficient separation between the TADF units to suppress aggregation-caused quenching (ACQ) and also assist in hole transport. Meanwhile, triazine acceptor groups are connected to each acridan unit as pendant groups, forming the active TADF sites. Density functional theory (DFT) calculations revealed that the HOMO is spread across the entire polymer backbone, whereas the LUMO is mainly confined to the pendant acceptor units. PAPTC shows a small singlet-triplet energy gap (ΔEST) of 0.13 eV, which is beneficial for efficient TADF. Its photoluminescence quantum yield (ΦPL) in toluene increased from 22% to 40% after nitrogen purging, confirming the suppression of oxygen-induced quenching. Non-doped single-polymer OLED (SP-OLED) devices based on PAPTC exhibited green emission at 521 nm and achieved a maximum external quantum efficiency (EQE_max) of 12.6% (Table 2).

Using a similar design strategy, Yang et al. (2018b) developed a series of TADF polymers with molecular weights between 6.3 and 17.6 kDa, retaining the same acridan-carbazole backbone but replacing the triazine acceptor with a benzophenone unit attached to the acridan. Among them, the best-performing polymer, PABPC5, contained 5% of the TADF monomer and showed a high Φ_PL of 77%. An undoped SP-OLED fabricated with PABPC5 delivered an impressive EQE_max of 18.1%, with CIE coordinates of (0.40, 0.56), and maintained excellent stability, as reflected by a high EQE₁₀₀₀ of 17.8% even at a brightness of 1,000 cd m^-2, indicating very low efficiency roll-off.

Liu et al. (2018) developed a TADF copolymer named COP-10 (Figure 5), which features a phenothiazine-carbazole backbone and incorporates 10% of a DBTO2-PTZ unit as the TADF-active monomer. SP-OLED devices fabricated using COP-10, doped at 10 wt% in a mixed TCTA:TAPC co-host system (65 wt%:25 wt%), achieved a maximum external quantum efficiency (EQE_max) of 15.7%. However, the device suffered from significant efficiency roll-off, with the efficiency decreasing by about 76% at a luminance of 100 cd m^-2.

Using a comparable molecular design approach, Zhao et al. (2022) reported two polymers, pBP-PXZ and pBP-PTZ, which consist of alkyl-substituted carbazole units copolymerized with 10% of either PXZ or PTZ donor groups. These donor units were connected to benzophenone acceptors, forming TADF-active segments within the polymer backbone (Figure 5). Both polymers had molecular weights of around 16 kDa and a polydispersity index (PDI) of 1.7. In neat films, they exhibited similar photoluminescence peaks at 550 nm, but their photoluminescence quantum yields (Φ_PL) differed significantly, reaching 82% for pBP-PXZ and 48% for pBP-PTZ (Table 2). The oxygen-containing polymer pBP-PXZ showed a slightly faster delayed fluorescence lifetime (τ_DF) of 1.29 μs compared to 1.55 μs for the sulfur-containing pBP-PTZ. Correspondingly, the non-doped SP-OLED based on pBP-PXZ delivered a higher maximum external quantum efficiency (EQE_max) of 13.7% with CIE coordinates of (0.52, 0.48), whereas the pBP-PTZ device achieved a lower EQE_max of 7.9% at CIE coordinates of (0.50, 0.49). In addition, the pBP-PXZ device exhibited a relatively smaller efficiency roll-off of 35% at a brightness of 1,000 cd m^-2, while the pBP-PTZ device was still capable of reaching the same luminance level. Further improvement was observed in doped devices, where incorporating 10 wt% pBN-PXZ into a CBP host increased the EQE_max to 23.1%, while maintaining an EQE above 19% at 1,000 cd m^-2 and reducing the efficiency roll-off to just 16%. These results represent some of the best performances reported for SP-OLEDs using TADF polymer emitters and clearly highlight the importance of optimizing the host-monomer combination to achieve high efficiency and device stability.

Wei et al. (2017) introduced an innovative strategy to achieve TADF by designing a macrocyclic polymer, P1, formed through the coupling of non-TADF monomers (Figure 5). In this system, the cyclization enhances donor conjugation, enabling the macrocycle itself to exhibit TADF properties. Photophysical studies and DFT calculations of P1, dispersed at 2 wt% in polystyrene, showed a high photoluminescence quantum yield (Φ_PL) of 71%, which is a significant improvement compared to only 3% for the corresponding monomer. Notably, delayed fluorescence contributed 51% of the total emission (Φ_DF), and the material displayed a relatively small singlet-triplet energy gap (ΔE_ST) of 0.19 eV, confirming efficient TADF behaviour. Although OLED devices based on P1 were not fabricated to assess its device performance, subsequent work explored how gradual expansion of conjugation in related cyclic oligomers influences their photophysical properties, providing further insight into the role of macrocyclization in promoting TADF (Wei et al., 2017).

Zhang et al. (2022) reported a polymer, PxPhO (Figure 5), constructed entirely from TADF-active monomer units. In this design, each repeating unit consists of a ketone acceptor connected to a poly (phenoxazine) donor backbone. Compared to the monomer, the polymer showed a significant red shift in its toluene emission, with the photoluminescence peak appearing at 557 nm, approximately 70 nm longer in wavelength. Despite this shift, the polymer maintained a very small singlet-triplet energy gap (ΔE_ST) of 0.07 eV, which is comparable to that of the monomer (ΔE_ST = 0.05 eV). Time-resolved photophysical studies revealed notable differences in the fluorescence lifetimes. The prompt fluorescence lifetime (τ_p) of the polymer was about three times shorter than that of the monomer (3.63 ns vs. 12.02 ns), whereas the delayed fluorescence lifetime (τ_d) of the monomer was nearly seven times longer than that of the polymer (0.054 μs vs. 0.008 μs). However, since the photoluminescence quantum yields of the polymer (>60%) and the monomer (∼50%) were quite similar, these lifetime differences are mainly attributed to faster reverse intersystem crossing (RISC) in the polymer, rather than increased non-radiative decay. In doped SP-OLED devices where the emitting layer consisted of 80 wt% mCP as the host and 20 wt% emitter, the polymeric emitter (PPxPhO) showed better performance than its monomeric counterpart (PxPhO). The device based on the polymer achieved a higher maximum external quantum efficiency (EQE_max) of 11.8% with electroluminescence at 550 nm, whereas the monomer-based device reached only 8.8% EQE_max with emission at 520 nm. The researchers attributed this improvement mainly to the superior film-forming ability of the polymer, which helps create more uniform and stable emissive layers, leading to enhanced device efficiency.

In another study, Wang et al. (2017) developed a series of TADF polymers named PFSOTT-x (Figure 5). These polymers were designed using a backbone composed of alternating fluorene and dibenzothiophene-S,S-dioxide units. The TADF functionality was introduced through a structure containing a triphenylamine donor and a thioxanthone-dioxide acceptor, enabling efficient thermally activated delayed fluorescence. These polymers showed relatively high molecular weights in the range of 48.2–58.3 kDa and broad molecular weight distributions. In thin films, their photoluminescence spectra gradually shifted from blue to orange as the proportion of the TADF monomer increased, reflecting stronger charge-transfer character with higher TADF content.

Although PFSOTT0.5, containing only 0.5% of the TADF unit, exhibited a high photoluminescence quantum yield (Φ_PL) of 89% in the thin film, the corresponding non-doped OLED device showed poor performance, with a low maximum external quantum efficiency (EQE_max) of just 2.6% and CIE coordinates of (0.49, 0.49). This low efficiency was mainly attributed to inefficient charge balance within the device. However, significant improvement was achieved when the TADF content was increased. For example, when PFSOTT2 (containing 2% TADF unit) was used as an emitter at 40 wt% in an mCP host matrix, the device exhibited excellent electroluminescence performance, achieving an EQE_max of 19.4% with emission at 592 nm. This improvement was consistent with the near unity Φ_PL of the polymer in the mCP matrix. These results clearly emphasize the importance of designing TADF polymers with appropriate functional groups that not only enable efficient TADF emission but also promote balanced charge transport for high-performance OLED devices.

Circularly polarized luminescence (CPL) has previously been observed in chiral small-molecule TADF emitters (see Section 7). Extending this concept to polymers, Hu et al. (2019) reported the first chiral conjugated poly (carbazole-ran-acridine) polymer, P10 (Figure 6). This material was designed by incorporating achiral TADF co-monomers together with chiral alanine-based side groups, which introduce stereogenic centers into the polymer. P10 had a molecular weight of about 10 kDa and a polydispersity index (PDI) of 1.7. Using a polymeric emitter instead of a small molecule offered advantages such as improved thermal stability and easier solution processing. The polymer exhibited a luminescence dissymmetry factor (glum) of −1.39 × 10⁻³, confirming its CPL activity. In neat films, P10 showed green emission with a photoluminescence quantum yield (Φ_PL) of 10.3% and a delayed fluorescence lifetime (τ_d) of 1.3 μs. It also displayed aggregation-induced emission (AIE) behavior in the solid state. When used in a doped SP-OLED device (5 wt% in mCP), P10 produced green electroluminescence with CIE coordinates of (0.36, 0.52). However, due to its relatively low Φ_PL, the device achieved only a modest maximum external quantum efficiency (EQE_max) of 0.87%.

Teng et al. (2022) later reported a new class of circularly polarized TADF (CP-TADF) polymers and their application in SP-OLEDs. In contrast to the earlier design, the TADF unit itself was inherently chiral and was directly incorporated into the polymer backbone. This was achieved by polymerizing one of the carbazole donor sites of the chiral TADF unit together with a fluorene co-monomer, resulting in two enantiomeric polymers, S-P and R-P (Figure 6). Photophysical measurements of the neat films showed that both enantiomers exhibited very similar photoluminescence peaks, at 560 nm for S-P and 562 nm for R-P. When these polymers were used as doped emitters (10 wt%) in an mCP host, their emission shifted toward shorter wavelengths by about 13 nm compared to the neat films. The doped films also showed high photoluminescence quantum yields, reaching 76% for S-P and 72% for R-P, along with delayed fluorescence lifetimes (τ_d) of 2.3 μs and 1.6 μs, respectively, indicating efficient TADF behavior. The dissymmetry factors (glum) of the two enantiomeric polymers were measured to be +1.9 × 10⁻³ for S-P and −1.9 × 10⁻³ for R-P, confirming their strong circularly polarized luminescence with opposite handedness. When these polymers were used in doped SP-OLED devices (10 wt% in mCP), they delivered excellent performance. The maximum external quantum efficiencies (EQE_max) reached 15.8% for S-P and 14.9% for R-P, and both devices showed relatively low efficiency roll-off, with decreases of only 22% and 15% at a brightness of 1,000 cd m^-2. Both devices emitted yellowish-green light, with CIE coordinates of (0.41, 0.57). In addition, the circularly polarized electroluminescence (CPEL) values were +1.6 × 10⁻³ for S-P and −1.5 × 10⁻³ for R-P, demonstrating efficient transfer of chiral optical properties from photoluminescence to electroluminescence.

Freeman et al. (2017) proposed an innovative approach to achieve TADF in conjugated polymers by introducing an orthogonal acceptor group at the bridgehead position of alternating spirofluorene units. In this design, charge-transfer (CT) states and the resulting TADF originate from through-space interactions, rather than from direct conjugation between donor and acceptor units along the polymer backbone. In the polymer ASFCN (Figure 7), the donor backbone and acceptor side groups are connected through a non-conjugated sp³ carbon linkage. This structural feature effectively separates the electron and hole wavefunctions in space, minimizing their overlap. As a result, although this separation helps reduce the singlet-triplet energy gap, it also leads to a very low overlap between the frontier molecular orbitals. Because of this minimal orbital overlap, the radiative decay from the singlet state becomes slow, while non-radiative decay via the triplet locally excited (³LE) state becomes more significant. Consequently, the material exhibited a relatively low photoluminescence quantum yield (Φ_PL) of only 16%, with emission occurring around 520 nm (Table 2).

5 TADF polymers with main-chain donor-acceptor

Nikolaenko et al. (2015) introduced a new design strategy called the “intermonomer TADF” approach to achieve TADF in main-chain polymers (Figure 8). In this concept, TADF arises from interactions between donor and acceptor units located on adjacent repeating units, rather than within a single monomer. Using Suzuki polymerization, they synthesized a polymer named LEP (Figure 8) with a feed ratio of 5% spacer, 50% acceptor, and 45% donor monomers. The spacer consisted of an alkyl chain, while the acceptor and donor units were triazine and amine groups, respectively. In this structure, the triazine acceptor interacts with the neighbouring amine donor to generate charge-transfer states, which are responsible for the TADF emission and also help control the recombination zone within the device. The relatively high proportion of spacer monomers played an important role by ensuring uniform distribution of the emissive donor-acceptor units and reducing aggregation-caused quenching (ACQ), similar to previously reported systems. As a result, the LEP polymer showed a moderate photoluminescence quantum yield (Φ_PL) of 43% and a singlet-triplet energy gap (ΔE_ST) of 0.22 eV, confirming its TADF behaviour. The non-doped SP-OLED based on LEP exhibited green electroluminescence with CIE coordinates of (0.32, 0.56) and achieved a maximum external quantum efficiency (EQE_max) of 10%, demonstrating its potential as a main-chain TADF emitter.

In another study, Philipps et al. (2022) synthesized a series of three polymers composed of two acridan donor units and one benzophenone acceptor unit in each repeating segment (Figure 8). These donor and acceptor units were connected through non-conjugated spacers of different lengths to investigate how spacer length influences TADF behaviour and device performance. The results showed a clear improvement in OLED efficiency with increasing spacer length. The fully conjugated polymer with a phenyl spacer, P(Ph-Mac-BP), exhibited a relatively low EQE_max of 2.9%. In contrast, introducing non-conjugated alkyl spacers improved the performance, with P(C2-Mac-BP), containing an ethyl spacer, reaching an EQE_max of 6.7%, and P(C6-Mac-BP), containing a longer hexyl spacer, achieving the highest EQE_max of 7.1%. This trend indicates that longer non-conjugated spacers help reduce unwanted interactions between donor and acceptor units, improving TADF efficiency and overall device performance. He SP-OLED based on P(C6-Mac-BP) also showed the most stable performance among the series, with only an 8% decrease in EQE at 100 cd m^-2 and a 30% reduction at 1,000 cd m^-2, indicating significantly improved efficiency roll-off (Table 3). Moving beyond linear architectures, Sun et al. (2022a), Sun et al. (2022b) developed branched and cross-linked polymers using a post-deposition thermal annealing strategy. These materials incorporated carbazole spacer units along with a carbazole-benzonitrile TADF emissive core (Figure 8). After spin-coating and annealing, the resulting cross-linked films exhibited blue emission around 470 nm.

The photoluminescence quantum yields (Φ_PL) varied depending on the polymer structure. DV-3CzCN, which lacked carbazole spacer units, showed a Φ_PL of 36%, while DVCz-3CzCN exhibited an improved Φ_PL of 54%. The linear counterpart, DVCz-2CzCN, achieved the highest Φ_PL of 68%, demonstrating the beneficial role of carbazole spacers in enhancing emission efficiency. When these materials were used in non-doped, thermally annealed OLED devices, they produced sky-blue emission with CIE coordinates of approximately (0.16, 0.31), (0.15, 0.30), and (0.16, 0.21), confirming their suitability for blue-emitting OLED applications. The device based on DV-3CzCN showed very poor performance, with an EQE_max of only 0.8%. In contrast, the SP-OLEDs fabricated using DVCz-2CzCN and DVCz-3CzCN exhibited much better efficiencies, reaching EQE_max values of around 6% (Table 3). This improvement was mainly attributed to the branched polymer structure, which helped separate the TADF emissive cores and thereby reduced aggregation-caused quenching (ACQ), resulting in more efficient emission.

In a separate study, Sun et al. (2022c) proposed another approach by combining two different small-molecule TADF units, 2CzBn and 2CzTBn. These units were polymerized through vinyl-benzyl linkers to form copolymers with tunable emitter compositions (VBNx, Figure 8). Along with control polymers containing only one type of TADF unit, they developed two copolymers with mixed compositions: VBN10, consisting of 90% 2CzBn and 10% 2CzTBn, and VBN50, containing equal amounts (50:50) of both emissive units. This design allowed precise control over the photophysical properties and device performance by adjusting the ratio of the two TADF components. In this polymer, the authors claim that the 2CzBN units largely function as hosts and the 2CzTBN units function as guest emitters. Both copolymers had comparable photophysical characteristics in the neat film, with ΔPL of 74% and 70% for VBN10 and VBN50, respectively, and λ_PL at 488 and 497 nm. Comparing the non-doped SP-OLEDs with VBN10 to the device with VBN50, the former demonstrated improved performance with an EQE_max of 11.4% at CIE coordinates of 0.20, 0.38% vs. 9.1% at CIE coordinates of 0.21, 0.41. It is true that the two polymers’ identical emission spectra validated the theory that one TADF subunit serves as the host for the other. The copolymers showed clear improvements in their photophysical properties compared to the control homopolymers that contained only one type of emissive unit (VBN0 and VBN100). In neat films, the copolymers exhibited higher photoluminescence quantum yields (Φ_PL) along with shorter delayed fluorescence lifetimes (τd), indicating more efficient TADF processes. As a consequence, OLED devices fabricated using the homopolymers performed significantly worse. The devices based on VBN0 and VBN100 achieved relatively low maximum external quantum efficiencies (EQE_max) of only 3.1% and 4.9%, respectively. These results highlight the advantage of combining different TADF units within a single copolymer, as this approach enhances emission efficiency and overall device performance.

6 TADF polymers through space

TADF can also arise from Through-Space Charge Transfer (TSCT) interactions between donor and acceptor units, rather than through direct conjugation, as demonstrated in recent studies. Based on this concept, Shao et al. (Shao et al., 2017) developed blue-emitting TADF polymers using a non-conjugated polyethylene backbone. In their design, TADF originated from through-space interactions between triazine acceptor units and pendant acridan-based donor groups.

Among the synthesized materials, only P-Ac95-TRZ05 exhibited clear TADF behaviour. This was attributed to its very small singlet-triplet energy gap (ΔE_ST) of 0.019 eV and a relatively high photoluminescence quantum yield (Φ_PL) of 60% in the neat film. For comparison, a related polymer, P-TBAc95-TRZ05 (Figure 9), was also prepared as a control. However, this material did not show TADF because the bulky tert-butyl substitution increased the distance between the donor and acceptor units, weakening the through-space interaction required for efficient charge transfer (Hu et al., 2022).

When applied in non-doped SP-OLED devices, P-Ac95-TRZ05 delivered excellent sky-blue electroluminescence with CIE coordinates of (0.18, 0.27). The device achieved a high maximum external quantum efficiency (EQE_max) of 12.1% and showed minimal efficiency roll-off, maintaining an EQE of 11.5% even at a brightness of 1,000 cd m^-2 (Table 4). These results highlight the effectiveness of through-space donor-acceptor design in developing high-performance blue TADF polymer emitters. In a follow-up study, the same group reported another series of TSCT-TADF polymers, known as the P1-x series (Figure 9), using the same acridine donor and triazine acceptor units but with a different mode of connection between the donor and the polymer backbone. Unlike their earlier design, where the acridine donor was linked to the backbone through a phenyl ring attached to the nitrogen atom (10-phenyl position), in this case the donor was connected directly through the 2-position of the acridine ring. This structural modification significantly influenced the photophysical properties.

The copolymers P1-05, P1-10, and P1-20, containing 5%, 10%, and 20% acceptor units, respectively, showed progressively red-shifted emission in neat films, with photoluminescence peaks at 485, 489, and 492 nm. However, their photoluminescence quantum yields (Φ_PL) decreased with increasing acceptor content, reaching 54%, 47%, and 45%, respectively (Table 4). In addition, their singlet-triplet energy gaps (ΔE_ST) were around 0.04 eV, which is approximately twice as large as that of the previously reported P-Ac95-TRZ05 polymer. Among this series, the best device performance was achieved with P1-05. The corresponding non-doped SP-OLED exhibited a high EQE_max of 11.3% with CIE coordinates of (0.20, 0.37), which aligned well with its favourable optical properties. This study clearly demonstrates that the relative orientation and spatial arrangement of donor and acceptor units play a crucial role in determining TADF efficiency. Since through-space charge transfer depends strongly on molecular geometry rather than direct conjugation, careful structural design and precise control over donor-acceptor positioning are especially important for optimizing TSCT-based TADF polymers.

7 Standards for characterization and material reproducibility of TADF polymers

Unlike small-molecule emitters that possess a well-defined molecular weight and can be conveniently purified by sublimation, TADF polymers are subject to significant batch-to-batch variations that greatly impact their optoelectronic characteristics. A polymer’s Mw/PDI strongly affects the degree of chain entanglement and determines the local packing density of the amorphous polymer film and hence the interchain distance and the local Δ_EST distribution, as recently demonstrated by Liu et al. Specifically, small variations in the monomer’s chemical structure between two different synthesis batches can already lead to significant differences in the interchain distance for a given set of processing conditions. As such, it is of utmost importance that future reports on TADF polymers always state GPC results along with Mn, Mw, and PDI for each analysed sample to allow for rational benchmarking between different works. Similarly, a standardized procedure should be adopted in the field for reporting photophysical characteristics, as both transient PL decay traces (τ _TADF) and absolute PLQY values are critically dependent on the sample environment due to the long lifetime of TADF polymers’ triplet excitons. Thus, all studies should explicitly state whether the measurements were performed under nitrogen/argon atmosphere or in high vacuum (10^–5 mbar). Additionally, when preparing thin-film samples, the authors should describe the fabrication procedure (e.g., choice of solvent for spin-coating, annealing temperature), as it was shown that minor variations in the processing conditions can greatly impact the film’s nanostructure and morphology, and hence the local exciton-photon coupling strength. Most importantly, since EQE_max is highly dependent on the choice of charge-transport layers and their vertical arrangement, absolute PLQY values of the thin-film samples should always be reported alongside the EQE_max results for a given set of device architecture and processing conditions. This will allow for distinguishing between variations arising from the active layer itself and the differences introduced by the changes in the device architecture.

8 Conclusion and future outlook

In conclusion, significant progress has been made in recent years in the development of thermally activated delayed fluorescence (TADF) polymers through a variety of molecular design strategies, including donor-acceptor main-chain structures, pendant-type systems, through-space charge transfer architectures, and copolymer approaches. The examples discussed demonstrate that these materials can exhibit favourable photophysical properties, such as high photoluminescence quantum yields, small singlet-triplet energy gaps, and efficient delayed fluorescence, which translate into promising electroluminescent performance in SP-OLED devices. TADF polymers are particularly attractive as emitters because their polymeric nature helps reduce aggregation-caused quenching (ACQ), ensuring more stable emission in the solid state. In addition, their excellent film-forming ability and compatibility with solution-processing techniques, such as spin-coating and printing, make them highly suitable for low-cost, large-area, and flexible OLED fabrication. These advantages offer clear practical benefits over many conventional small-molecule emitters, especially from a manufacturing perspective.

However, despite these encouraging developments, TADF polymers still face challenges in reaching the performance levels of state-of-the-art small-molecule TADF emitters. In particular, further improvements are needed to achieve higher maximum external quantum efficiencies (EQE max), improved charge balance, and superior colour purity with narrower emission bandwidths (lower full width at half maximum, FWHM). To overcome these limitations and make TADF polymers truly competitive with small-molecule alternatives, the field must transition from refining single-component architectures toward adopting sophisticated hybrid strategies. While main-chain donor-acceptor (D-A) backbones provide robust mechanical films and superior intra-chain charge transport, they consistently suffer from extended conjugation that broadens emission bandwidths, alongside dense polymer packing that induces large Δ E ST. Conversely, pendant architectures and through-space charge transfer (TSCT) polymers excel at maintaining exceptionally small Δ E ST values and high PLQY by spatially isolating or rigidly decoupling the HOMO and LUMO on independent units, effectively mimicking the highly localized excited states of small molecules.

Therefore, the most promising avenue for surpassing current performance boundaries lies in the strategic copolymerization of rigid, high-efficiency TSCT or pendant monomers into highly stable, non-conjugated, charge-transporting backbones. This combination strategy ensures completely decoupled optoelectronic performance minimizing singlet-triplet splitting to maximize reverse intersystem crossing (RISC) rates, while independently optimizing ambipolar charge injection through the host backbone matrix. Continued efforts focusing on this hybrid molecular design framework, paired with standardized, rigorous characterization protocols, will be essential to fully realize the potential of solution-processed TADF polymers and bridge the gap between lab-scale efficiency and next-generation, large-scale industrial OLED commercialization.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Glossary

ACQ Aggregation-Caused Quenched/Aggregation-Caused Quenching A Acceptor (Electron Acceptor) CIE Commission Internationale de l'Éclairage (International Commission on Illumination) CPL Circularly Polarized Luminescence CPEL Circularly Polarized Electroluminescence CT Charge Transfer D Donor (Electron Donor) D-A Donor-Acceptor DFT Density Functional Theory Δ _**EST** Singlet-Triplet Energy Splitting EGL Energy Gap Law EL Electroluminescence EML Emissive Layer EQE External Quantum Efficiency ETL Electron Transport Layer *f* Oscillator Strength FWHM Full-Width at Half-Maximum HIL Hole Injection Layer HOMO Highest Occupied Molecular Orbital HTL Hole Transport Layer λ _**PL** Photoluminescence Emission Maximum Wavelength λ _**EL** Electroluminescence Emission Maximum Wavelength IQE Internal Quantum Efficiency ISC Intersystem Crossing ITO Indium Tin Oxide *k* _**nr** Non-Radiative Decay Rate *k* _***RISC*** Reverse Intersystem Crossing Rate LUMO Lowest Unoccupied Molecular Orbital NIR Near-Infrared NTSC National Television System Committee OLED Organic Light-Emitting Diode Φ _**PL** Photoluminescence Quantum Yield τ _**D** delayed fluorescence lifetime PL Photoluminescence RISC Reverse Intersystem Crossing S _**0** Ground State S _**1** Lowest Singlet Excited State SP-OLED Solution-Processed Organic Light-Emitting Diode T _**1** Lowest Triplet Excited State TADF Thermally Activated Delayed Fluorescence TDDFT Time-Dependent Density Functional Theory TPQ Triplet-Polaron Quenching TSCT Through-Space Charge Transfer TTA Triplet-Triplet Annihilation UV-Vis Ultraviolet-Visible Spectroscopy V _**on** Turn-on Voltage WOLED White Organic Light-Emitting Diode TCTA Tris(4-carbazoylphenyl)amine PS Polystyrene TAPC-4,4′ Cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] CBP-4,4′ Bis(N-carbazolyl)-1,1′-biphenyl mCP-1,3 Bis(N-carbazolyl)benzene 5TCzCN 2,3,4,5,6-Pentakis(9H-carbazol-9-yl)benzonitrile.

Footnotes

Edited by: Mohit Garg, Birla Institute of Technology and Science, India

Reviewed by: Keshavanandaprabhu P., Gachon University, Republic of Korea

Georgina L. Gregory, University of Oxford, United Kingdom