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A photocrosslinkable donor, PM6-X30, has been designed by engineering the side chains of the PM6 backbone. A high PCE of 12.33% was achieved with significantly enhanced thermal stability.

New photocrosslinkable conjugated donor–acceptor block copolymer bearing oxetane side chains is synthesized by one-pot polymerization to improve the thermal and morphological properties.

A polymer and a small molecule were developed as a mixed host with an exciplex for high performance of green TADF OLEDs.

Three V-shaped host molecules with a cyclohexane linker were successfully synthesized for thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The unipolar host molecules, BBCzC and BTDC, contained two 9-phenyl-9H-3,9'-bicarbazole (PBCz) moieties and two 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (PDBNA) moieties, respectively. BCzTC, a bipolar host molecule, consisted of a donor unit, PBCz, and an acceptor unit, PDBNA, connected by a cyclohexane linker. Three host molecules showed good solubility in various organic solvents, making them suitable for solution processing. Among the solution-processed green TADF-OLEDs using three host molecules and a green TADF emitter, the one with BCzTC showed the highest external quantum efficiency of up to 30% with a high power efficiency of 71 lm W-1 and a current efficiency of 102 cd A-1. Compared with BBCzC and BTDC, BCzTC exhibited a relatively high photoluminescence quantum yield (PLQY), an excellent balance in hole and electron transport properties in the emitting layer, and more efficient energy transfer to the emitter, giving such an excellent device performance.

New wide-bandgap donor-acceptor-π type conjugated polymers, PBTTT and PBTDTT, containing different π-extended conjugated bridges between benzodithiophene (BDT) as a donating unit and 3-carboxylthiophene (3CT) as a weak electron-withdrawing group, were successfully synthesized and employed as donor polymers for polymer solar cells. Thienothiophene (TT) and dithienothiophene (DTT) were selected as fused thiophene bridges for inclusion in the polymer backbone instead of a single thiophene. As a control donor polymer, PBTT containing a single thiophene bridge was also prepared. Its properties were compared with those of PBTTT and PBTDTT. As the conjugation length of the p-extended bridge (i.e., from thiophene to DTT) increased, the bandgap of the polymer slightly decreased, and the highest occupied molecular orbital level shifted to a higher-lying level. Compared to PBTT, PBTTT and PBTDTT exhibited relatively low solubility and red-shifted absorption spectra in solution states. PBTTT and PBTDTT showed strong aggregation between polymer chains, even in solution states, which were similar to the film state. Among the three copolymers, PBTTT-based non-fullerene polymer solar cells (NF-PSCs) with ITIC-Me showed a high power conversion efficiency of 7.30% with a high short circuit current density of 14.05 mA/cm2. The superior performance of the NF-PSCs based on PBTTT may be attributed to their predominant face-on orientation of polymer chains and relatively more favorable surface morphology.

Silver nanowire (AgNW) electrodes are among the most essential flexible transparent electrodes (FTEs) emerging as promising alternatives to brittle indium tin oxide (ITO) electrodes. The polymer comprising the plastic substrate to which the AgNWs are applied must also satisfy the mechanical requirements of the final device and withstand the device processing conditions. However, AgNW-based FTEs have some limitations, such as poor adhesion to coated plastic substrates, surface roughness, and difficulty in patterning. This study demonstrates a new strategy for creating AgNW-based patterned flexible poly(ethylene 2,6-naphthalate) (PEN)-based electrodes with appreciable optical and electrical properties. Introducing poly(2-hydroxyethyl methacrylate) on the PEN substrate enhanced the adhesion between the substrate and AgNWs and improved the dispersibility of the AgNWs. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and a small amount of 2,4-hexadiyne-1,6-diol as a photosensitizer were coated onto the AgNW layer to improve the surface roughness and achieve an effective electrode pattern. By varying the AgNW concentration, we could tune the density and thickness of the AgNWs to optimize the sheet resistance and transmittance. Optimized AgNWs with a sheet resistance of 22.6 Ω

Conjugated random terpolymers, PJ-25, PJ-50, and PJ-75 were successfully synthesized from three different monomers. Fluorine-substituted benzotriazole (2F-BTA) was incorporated into 4,8-bis(4-chlorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (BDT-T-Cl) and a 1,3-bis(4-(2-ethylhexyl)thiophen-2-yl)-5,7-bis(2-alkyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione (BDD)-based alternating copolymer PM7 as a third monomeric unit. The solubility of the random terpolymers in nonhalogenated solvents increased with the number of 2F-BTA units in PM7. The random terpolymers were mixed with 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (IT-4F) to fabricate organic photovoltaic (OPV) cells. Among the three terpolymers and two related binary copolymers (e.g., PM7 and J52-Cl), outdoor photovoltaic (PV) cells (AM 1.5G) based on the PJ-50:IT-4F blend showed a high power conversion efficiency (PCE) of 11.34%. In addition, PJ-50 was employed as a donor in indoor PV (IPV) cells and was blended with nonfullerene acceptors, which have different absorption ranges. Among them, the PJ-50:IT-4F-based IPV device had the highest PCE of 17.41% with a Jsc of 54.75 μA cm-2 and an FF of 0.77 under 160 μW cm-2 light-emitting diode (LED) light. The terpolymer introduced in this study can be regarded as a promising material for the fabrication of outdoor PV and IPV cells with excellent performance involving the use of an eco-friendly solvent.

Two new hole transport styrene polymers, 2DMFCz and 2DBFCz, were successfully synthesized via radical polymerization. The design concept aims to investigate the hole-transporting ability and energy-level tunability by introducing bis(9,9-dimethyl-9H-fluoren-2-yl)aminocarbazole and bis(dibenzo[b,d]furan-2-yl)aminocarbazole as side-chain pendants. They were found to show good solubility in chlorobenzene but poor solubility in toluene, similar to poly(9-vinylcarbazole) (PVK). The highest occupied molecular orbital levels of 2DMFCz and 2DBFCz were determined to be −5.23 eV and −5.31 eV, respectively, while hole mobilities were estimated to be 1.65 × 10−7 cm2 V−1 s−1 and 1.48 × 10−8 cm2 V−1 s−1 measured by the space-charge limited-current method. Subsequently, in solution-processed green thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs), the 2DMFCz- and 2DBFCz-based devices exhibited a relatively low turn-on voltage of 2.7 V and higher maximum external quantum efficiencies of 23.84% and 21.11%, respectively. These values were superior to those of a PVK-based device. The polymer hole-transport materials presented in this study are promising materials that can play a significant role in improving the performance of TADF-OLEDs fabricated through a solution process in the future.

Herein, a novel hole transport polymer, P-CzAc, for solution-processed green quantum dot light-emitting diodes (QD-LEDs) was synthesized. P-CzAc consists of a polystyrene backbone and 10-(9H-carbazol-3-yl)-9,9-dimethyl-9,10-dihydroacridine as side-chain pendants. The design strategy aims to improve the hole transportability and achieve the low-lying highest occupied molecular orbital (HOMO) level for P-CzAc for reducing the charge injection barrier from the hole injection layer to the hole transport layer. P-CzAc showed good solubility in tetrahydrofuran, methylene chloride, and aromatic solvents, but high solvent tolerance for hexane and octane, similar to poly(N-vinylcarbazole) (PVK). Compared to PVK (HOMO = −5.58 eV), P-CzAc exhibited a relatively high-lying HOMO level of −5.33 eV. In particular, the hole mobility (μh) of P-CzAc was estimated to be 2.24 × 10−6 cm2 V−1 s−1, which is much higher than that of PVK (μh = 4.11 × 10−9 cm2 V−1 s−1). In solution-processed green QD-LEDs, the P-CzAc-based device exhibited a relatively low turn-on voltage (Von) of 2.8 V and a high maximum external quantum efficiency (EQE) of 11.6%. In comparison with a PVK-based device (Von = 4.4 V; EQE = 8.6%), the P-CzAc-based device is more efficient owing to the significant improvement in hole injection.

In this study, polyethylene 2,6-naphthalate (PEN) was selected as a substrate to fabricate a flexible conducting electrode through the solution process. The sandwiched silver nanowire (AgNW) electrode between the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layers fabricated on the flexible PEN substrate was successfully prepared, which exhibited a moderately high electrical conductivity and surface smoothness suitable for polymer solar cells. Notably, the sheet resistance of the PEDOT:PSS/AgNW/PEDOT:PSS film was 22 Ω/□, and it exhibited the transmittance of 82% at the wavelength of 550 nm, although PEN was used as the substrate. This electrode film can be easily employed as an anode, and when it is applied as an electrode in a polymer solar cell, it reveals a comparable performance to that of indium tin oxide-based devices. This simple and effective fabrication of flexible conductive electrodes is envisaged to contribute immensely to future research on flexible electronics and optoelectronics.

Recently, various host materials have been developed for solution-processed thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Compared with small-molecule hosts, polymeric hosts are advantageous for inducing a uniform distribution and segregation of dopant molecules in the emissive layer without undesired large-scale phase separation. In this study, new polymer hosts were demonstrated, in which a bipolar conjugative moiety consisting of a carbazole (Cz) donor and an α-carboline (α-Cb) acceptor was bound to the polystyrene backbone through a non-conjugated linker. They exhibited high triplet energies of >2.8 eV, and their emission spectra overlapped with the absorption spectrum of a green TADF emitter, which allowed facile energy transfer from the polymeric host to the small-molecule dopants. High device performance was observed, with external quantum efficiencies (EQEs) of 13.65, 17.09, and 17.48% for solution-processed green TADF-OLEDs using PSCzCz, PSCzCb, and PSCbCz, respectively, as hosts for the EML. The EQEs of bipolar host (PSCzCb and PSCbCz)-based devices were higher than those of unipolar host (poly(N-vinylcarbazole) and PSCzCz)-based devices owing to the well-balanced charge-carrier transport. According to these results, the polymeric host bearing a bipolar Cz and α-Cb coupled moiety is a promising material for solution-processable TADF-OLEDs.

The use of soluble host materials and thermally activated delayed fluorescence (TADF) emitters is indispensable for developing high-efficiency organic light-emitting diodes (OLEDs) by cost-effective solution processes. In this study, two bipolar hosts were designed as structural isomers, namely 3-(3,5-di(9H-carbazol-9-yl)phenyl)-9H-xanthen-9-one (Xp-mCP) and 2-(3,5-di(9H-carbazol-9-yl)phenyl)-9H-xanthen-9-one (Xm-mCP). The two host materials were synthesized by combining the unipolar host, 1,3-di(9H-carbazol-9-yl)benzene (mCP) with 9H-xanthen-9-one as an electron-accepting moiety. The two hosts exhibit good solubility in various organic solvents and high triplet energy (ET = 2.67 eV for Xp-mCP and ET = 2.82 eV for Xm-mCP), which renders them suitable for t4CzIPN-containing solution-processable green TADF-OLEDs. The maximum external quantum efficiency (EQE) values were 19.3% and 22.0% for Xp-mCP- and Xm-mCP-based green TADF-OLED, respectively. Among them, the device comprising Xm-mCP showed an excellent efficiency roll-off behavior by displaying only a 4.5% decrease and 11.4% decrease at 1000 cd m−2 and 2000 cd m−2, respectively. These results show the significant potential of xanthone-mCP host materials to develop solution-processable OLED technologies.

The development of bipolar host materials for solution-processable thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs) is challenging because few host materials for TADF-OLEDs have been reported. Solution-processable bipolar host materials should have good solubility in various organic solvents and should exhibit good thermal stability and film-forming properties. In this study, three bipolar host materials (i.e.Py2Cz, Py2BFCz, and Py2ICz) for solution-processable green-emitting TADF-OLEDs were synthesized by coupling 2,4-diphenylpyrimidine to mCP and modifying the carbazole-donating units in the mCP structure. Thus, the effects of different host structures on the performance of green TADF-OLEDs could be investigated. The three host materials exhibited high thermal stability and fine morphologies in film states. Therefore, all three host materials were utilized to fabricate solution-processed green TADF-OLEDs with a green-emitting dopant. Particularly, the Py2ICz-based device displayed outstanding performance with a maximum external efficiency of 24.1% because Py2ICz has superior charge balance in the emitting layer than the others. These results unambiguously demonstrated that mCP derivatives with a pyrimidine core are suitable bipolar host materials for solution-processed green TADF-OLEDs.

In this study, two polymeric host materials, P(NmCP) and P(mCP), were synthesized, and high-performing sky-blue and green thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs) were achieved. The simple structure polymer host was designed by inserting a pyridine group into the core of P(NmCP) and an electron-donating phenyl group into the core of P(mCP). The two polymeric hosts exhibited high triplet energies (T1 = 3.04 eV for P(NmCP) and 3.05 eV for P(mCP)), which were sufficiently high to realize blue and green TADF-OLEDs. In brief, solution-processed OLEDs with an emissive layer bearing P(NmCP) as a bipolar electron host exhibited remarkable performance with a maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 70.36 cd A−1, 63.15 lm W−1, and 20.07%, respectively, in the green-emitting device. In the blue-emitting device, we obtained a maximum CE, PE, and EQE of 27.13 cd A−1, 22.30 lm W−1, and 10.70%, respectively. The polymer design with such a high T1 value is believed to be the cornerstone for implementing high-performance TADF-OLEDs via solution processing in the future.

We successfully synthesized a crystalline main chain conjugated copolymer, P(BDBT-co-NDI2T), having BDBT donor-NDI2T acceptor heterojunctions in the film state. Interestingly, the polymer exhibited a strong absorption band from 500 to 650 nm, which overlapped well with the emission spectrum of white light-emitting diodes (LEDs) used as an indoor light source. The P(BDBT-co-NDI2T) films had a relatively smooth surface and internal morphology compared to the blend films of P(BDBT) and P(NDI2T). In particular, the Kelvin probe force microscopy data explained the increased uniformity in the distribution of the surface charge in the annealed P(BDBT-co-NDI2T) films as compared to those of the annealed blend films of P(BDBT) and P(NDI2T). Indoor photovoltaics (IPVs) produced by using the P(BDBT-co-NDI2T) synthesized in this study as an active layer showed a high power conversion efficiency of 12.70% (@500 lux) with a short circuit current density of 49.89 μA cm−2. The PCE of the P(BDBT-co-NDI2T) film-based IPVs was twice as high as that of the blend film-based IPVs and showed excellent operational stability. This study is the first time that the P(BDBT-co-NDI2T) has been applied in IPVs, which suggests the potential for their widespread use in the development of indoor organic PVs in the future.

A new photocrosslinkable hole-transporting homopolymer (PX2Cz) was successfully synthesized using 9-((3-methyloxetan-3-yl)methyl)-9′-(4-vinylbenzyl)-9H,9′H-3,3′-bicarbazole monomer via radical polymerization. Biscarbazole, as a hole-transporting material, has two reactive sites that can introduce a radical polymerizable styrene moiety and a photocrosslinkable oxetane moiety. The photocuring temperature and time for the PX2Cz film was optimized to be 120 °C and 10 s. The photocured films showed good solvent resistance, which is favorable for the deposition of an emitting-layer solution on them. In particular, the highest occupied molecular orbital (HOMO) energy of the as-cast PX2Cz film was determined to be −5.37 eV which remained unchanged even after photocuring, thus facilitating hole transportation from the hole-injection layer. Subsequently, solution-processed, green, thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs) were manufactured using PX2Cz as the hole-transport material. The devices displayed a notable performance with an exceptionally low turn-on voltage (Von) of only 2.8 V and a high external quantum efficiency (EQE) of 22.5%; these values are substantially better than those of commonly used poly(9-vinylcarbazole) (PVK)-based OLEDs (Von = 3.6 V, EQE of 15.5%). The remarkably low turn-on voltage and high EQE were ascribed to the shallower HOMO energy level and more pronounced hole-transport ability of the photocured PX2Cz film.

In this study, we demonstrated two deep-blue TADF emitters, BO-tCzPhICz and BO-tCzDICz, for solution-processable thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). They were synthesized by employing an organoboron acceptor and 9-(3,6-di

Silver nanowires (AgNWs) are one of the important flexible electrode material candidates that can replace brittle indium tin oxide (ITO). In this work, we demonstrated novel patterned sandwich-type AgNW-based transparent electrodes easily prepared using the photolithography method for application in flexible devices. A cross-linked underlayer was introduced to increase the adhesion properties between a poly(ethylene terephthalate) substrate and AgNWs, and as a result, a uniform AgNW layer was easily deposited. Finally, the AgNW layer could be easily patterned by introducing a photocross-linkable upper layer without lift-off, dry transfer, and removal methods. A mixture of poly(sodium-4-styrene sulfonate) (PSS

This study demonstrated the use of a thermally crosslinked polyimide (PI) for the liquid crystal (LC) alignment layer of an LC display (LCD) cell. Polyamic acid was prepared using 4,4′-oxydianiline (ODA) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA). The 6FDA−ODA-based polyimide (PI) prepared by the thermal cyclic dehydration of the polyamic acid (PAA) was soluble in various polar solvents. After forming a thin film by mixing trifunctional epoxide [4-(oxiran-2-ylmethoxy)-N,N-bis(oxiran-2-ylmethyl)aniline] with the 6FDA−ODA-based PAA, it was confirmed that thermal curing at −110 °C caused an epoxy ring opening reaction, which could result in the formation of a networked polyimide not soluble in tetrahydrofuran. The crosslinked PI film showed a higher rigidity than the neat PI films, as measured by the elastic modulus. Furthermore, based on a dynamic mechanical analysis of the neat PI and crosslinked PI films, the glass transition temperatures (Tgs) were 217 and 339 °C, respectively, which provided further evidence of the formation of crosslinking by the addition of the epoxy reagent. After mechanical rubbing using these two PI films, an LC cell was fabricated using an anisotropic PI film as an LC alignment film. LC cells with crosslinked PI layers showed a high voltage holding ratio and low residual direct current voltage. This suggests that the crosslinked PI has good potential for use as an LC alignment layer material in advanced LCD technologies that require high performance and reliability.

In this study, a novel wide-bandgap conjugate donor-acceptor type copolymer, PBDT-TFMTh, containing benzodithiophene (BDT) as a donor unit and trifluoromethyl (TFM)-substituted thiophene (T...

A new side-chain polymer (X-TPACz) bearing hole-transporting pendant groups accompanying a thermally crosslinkable entity was synthesized using N-([1,1'-biphenyl]-4-yl)- N-(4-(9-(4-vinylbenzyl)-9 H-carbazol-3-yl)phenyl)bicyclo[4.2.0]octa-1(6),2,4-trien-3-amine (6) via addition polymerization. The X-TPACz could be spontaneously crosslinked without using any further reagents and showed a good film-forming property upon low-temperature thermal treatment. The thermal curing temperature for the X-TPACz film was optimized to be 180 °C based on a differential scanning calorimetry thermogram. Moreover, the thermal degradation temperature of X-TPACz measured to be over 467 °C using thermogravimetric analysis demonstrated that it shows excellent thermal stability. In particular, X-TPACz exhibits the highest occupied molecular orbital (HOMO) energy level to be -5.26 eV, which is beneficial for facile hole injection and transportation. Consequently, the thermally activated delayed fluorescence organic light-emitting diodes fabricated using X-TPACz as the hole-transporting material showed state-of-the-art performances with a low turn-on voltage ( Von) of only 2.7 V and a high external quantum efficiency (EQE) of 19.18% with a high current efficiency (CE) of 66.88 cd/A and a high power efficiency (PE) of 60.03 lm/W, which are highly superior to those of the familiar poly(9-vinylcarbazole) (PVK)-based devices ( Von = 3.9 V, EQE of 17.42%, with CE of 58.33 cd/A and PE of 33.32 lm/W). The extremely low turn-on voltage and high EQE were found to be due to the higher-lying highest occupied molecular orbital energy level ( EHOMO = -5.23 eV) and better hole-transporting property of X-TPACz than those of PVK.

This study reports the design, synthesis, and characterization of two new bipolar host materials, DCzCP and TCzCP. Both materials were implemented as hosts by doping a known green thermally activated delayed fluorescent (TADF) emitter (t4CzIPN) in solution-processable OLEDs. DCzCP-based devices afford the best performance with the maximum external quantum efficiency (EQE) of 21.2%. Notably, the EQE was maintained at 20.7% and 19.7% at a practical luminance of 500 cd m-2 and 1000 cd m-2, respectively, demonstrating very small roll-off.

A series of conjugated terpolymers, P2–P4, based on 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene as the electron-donating unit, methyl-3-thiophenecarboxylate (3MT) as the weak electron-accepting unit, and 1,3-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) as the strong electron-accepting unit were synthesized to investigate the effect of the contents of 3MT and BDD on their optical and electrochemical properties and the performance of the derived fullerene-free polymer solar cell (PSC) devices. By varying the contents of 3MT and BDD in the terpolymer structure, the solubility, absorption range, and energy levels could be efficiently tuned. Among the three terpolymers, the as-cast blend film of P3:acceptor with complementary absorption and favorable internal morphology exhibited the highest power conversion efficiency of 10.26% with a high open circuit voltage of 0.94 V and short circuit current density of 17.18 mA cm−2 in the PSC. Although the three repeating units were randomly arranged along the polymer backbone, their PSCs exhibited an excellent shelf-life of over 1000 h under ambient conditions, which is as good as those of binary D–A copolymers.

Thermally activated delayed fluorescence (TADF) materials have attracted significant attention owing to their state-of-the-art performance in the field of organic light-emitting diodes (OLEDs). TADF materials have the capability of harvesting both singlet and triplet excitons through reverse intersystem crossing, thus, the maximum internal quantum efficiency can be expected to be 100%. Thanks to TADF materials that are developed from pure organic entities so that they are inexpensive and external quantum efficiencies as high as 38% have been achieved to date. Despite the high performance of doped OLEDs, precise control of the host–guest ratio and phase separation at high driving voltages are the foremost challenges. In order to circumvent these demerits, the use of numerous small molecules, dendritic molecules, and polymers as non-doped emitters has been reported. Non-doped OLEDs consist of only a single molecule emitter in the emissive layer, thus simplifying the device fabrication process. Furthermore, non-doped OLEDs exhibit better device stability compared to doped devices, because the former do not exhibit phase separation or crystallinity and maintain a homogeneous surface film morphology during device operation. As a result, non-doped OLEDs are capable of overcoming the most pivotal issues of device complexity and stability, which makes them effective in rendering OLEDs commercially viable. Although maximum external quantum efficiencies of nearly 23.0% in blue, 22.0% in green, 22.0% in yellow, 17.0% in orange, and 10.0% in red emitting materials have been realized with non-doped OLEDs, still further progress is essential to reach the doped devices. This review systematically describes the molecular design, photophysical properties, and electroluminescence performance data of non-doped TADF emitters. We strongly believe that this review will be beneficial in terms of presenting a specific direction for the design of a variety of non-doped TADF emitters in the near future.

Highly soluble functional materials acting as hosts for thermally activated delayed-fluorescence (TADF) emitters are urgently needed to stimulate the development of cost-effective, solution-processable, high-performance organic light-emitting diodes (OLEDs). An organic material, 10-(6-(9H-carbazol-9-yl)pyridin-3-yl)-9,9-diphenyl-9,10-dihydroacridine (APC), was designed and facilely synthesized by integrating electron-donating diphenyl acridine and carbazoles at the 2- and 5-positions of electron-accepting pyridine (D–A–D′ type architecture). The high triplet energy (2.82 eV), thermal robustness (thermal decomposition beyond 350 °C), appropriate highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels, balanced charge-carrier transport ability, and good solubility of APC supported its designation as a host material for solution-processable TADF-OLEDs. Two different types of TADF OLEDs were fabricated by varying the hole transport material (HTM) while consistently using APC as the host and familiar t4CzIPN as the green TADF emitter, and their device characteristics were compared. At first, the devices fabricated using PVK as HTM (ITO/PEDOT:PSS/PVK/EML/TPBi/LiF/Al) that could use an orthogonal solvent system displayed a state-of-the-art performance with external quantum efficiency (EQE)/current efficiency (CE)/power efficiency (PE) as high as 24.0%/82.2 cd A−1/46.9 lm W−1, respectively. In particular, over 90.0% of EQE was retained (EQE of 21.7%) at the practical luminance of 1000 cd m−2, which is advantageous for display technology. Another class of devices was fabricated by replacing PVK with our recently reported thermally cross-linkable X-TPACz as the HTM, realizing a very low turn-on voltage (2.9 V) and excellent PE of 70.1 lm W−1 (with a similar EQE of 22.8%), which could be very effective for lighting equipment. These excellent outcomes demonstrate the potential of APC as a host material for future solution-processable display and lighting technologies.

Conjugated block copolymers containing donor (D) and acceptor (A) blocks have high potential for single component polymer solar cells (SC-PSCs), but still exhibit the complexity of polymer synthesis and low device efficiency. In this research, we successfully synthesized a new fully conjugated D–A block copolymer (CDABP) by performing the entire reaction in one-pot from start to completion. This polymerization method has the advantage of saving synthesis time and cost. The photoluminescence (PL) of the CDABP film was completely quenched due to photoinduced inter/intramolecular charge transfer. A single component polymer solar cell (SC-PSC) with a CDABP film annealed at 180 °C showed the maximum power conversion efficiency (PCE) of 5.28%, a high short circuit current of 10.77 mA cm−2 and a fill factor of 62.86%, which is much higher than that (2.62%) of the device with the as-cast film. This performance can be attributed to its fine internal/surface morphology and high crystallinity of the CDABP film. In addition, transient absorption experiments on the CDABP films showed that charge carrier generation is faster and the lifetime of the generated charge carriers is longer in the annealed film than in the as-cast film. Our research explicitly provides a new structural design and simple synthesis strategy for D–A conjugate block copolymers for high-efficiency SC-PSCs.

In this study, we have synthesized a new asymmetric n-type semiconducting molecule (Me-ITBD) by combining 4,4-bis(4-hexylphenyl)-7-methyl-6-(thiophen-2-yl)-4H-indeno[1,2-b]thiophene with 2-(benzo[c][1,2,5]-thiadiazol-4-yl methylene)-malononitrile and applied it to polymer solar cells. Compared to the PhITBD acceptor without methyl substituent in the 7-position of the core, Me-ITBD showed a larger torsional angle between thiophene and indenothiophene. Non-fullerene polymer solar cells (PSCs) with the methyl-substituted asymmetric acceptor Me-ITBD displayed an enhanced power conversion efficiency (PCE) of 5.75%, compared to the PSC (PCE = 1.79%) based on a PhITBD acceptor. The higher PCE value of the Me-ITBD-based PSC was ascribed to its improved device parameters, i.e. the Jsc and FF, induced by a favorable fine morphology in the active layer. By simply introducing a methyl substituent in the indenothiophene unit of the PhITBD acceptor, the PSC performance was enhanced.

The photophysical properties of donor (D)-acceptor (A) polymers were studied by designing two types of polymers, (D-σ-A)n and (D-π-A)n , with non-conjugated alkyl (sp3) and π-conjugated (sp2) linkers using π-extended donor and acceptor monomers that exhibit planar A-D-A structures. The non-conjugated alkyl linker provides structural flexibility to the (D-σ-A)n polymers, while the π-conjugated linker retains the rigid structure of the (D-π-A)n polymers. Photoinduced energy transfer occurs from the large donor to acceptor units in both polymers. However, the photoinduced energy transfer dynamics are found to be dependent on the conformation of the polymers, where the difference is dictated by the types of linkers between the donor and acceptor units. In solution, intramolecular energy transfer is relatively favorable for the (D-σ-A)n polymers with flexible linkers that allow the donor and acceptor units to be proximally located in the polymers. On the other hand, intermolecular (or interchain) energy transfer is dominant in the two polymer films because the π-extended donor and acceptor units in polymers are closely packed. The structural flexibility of the linkers between the donor and acceptor repeating units in the polymers affects the efficiency of energy transfer between the donor and acceptor units and the overall photophysical properties of the polymers.