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In this study, two novel multiple resonance (MR) emitters, DtCzBN and Cy-DtCzBN, were designed based on the well-known BCzBN structure and synthesized for narrowband solution-processed organic light-emitting diodes (OLEDs). Cy-DtCzBN possesses a dimeric V-shaped structure formed by coupling two individual DtCzBN units via a nonconjugated cyclohexane linker. When compared with DtCzBN, Cy-DtCzBN, as a medium-sized molecule, was found to maintain the optical and photophysical properties of the corresponding monomeric unit, DtCzBN, but exhibits high thermal stability, excellent solubility, and good film-forming ability. Additionally, solution-processed OLEDs were fabricated by using two sets of molecules: one set of small molecular hosts and emitters (i.e., mCP and DtCzBN) and the other set of medium-sized molecular hosts and emitters (i.e., Cy-mCP and Cy-DtCzBN). Notably, devices using medium-sized molecular hosts and emitters exhibited similar optical and photophysical properties but showed significantly improved reproducibility and thermal stability compared with those based on small molecular hosts and emitters. Our current study provides some insights into molecular design strategies for thermally stable hosts and emitters, which are highly suitable for solution-processed OLEDs.

In solution-processed organic light-emitting diodes (OLEDs), achieving high color purity and efficiency is as important as that in vacuum processes. Emitters suitable for solution processing must have excellent solubility in organic solvents, high molecular weight, and compatibility with the host materials. In this study, we synthesized a deep-blue emitter that satisfies the above conditions by introducing a 1,4-bis(indolo[3,2,1- jk ]carbazol-2-yl)benzene-based planar emitting core (DICz) structure and four 3,6-di- tert -butyl-9-phenyl-9 H -carbazole ( t Cz) peripheral units, namely, 4 t Cz-DICz. A comparative compound, 4Hex-DICz, incorporating hexyl phenyl groups was synthesized. In contrast to 4Hex-DICz, 4 t Cz-DICz exhibited exceptional solubility in organic solvents and superior film-forming properties attributed to the presence of t Cz units. Additionally, in the film state, the effective encapsulation of the emitting core (DICz) by the t Cz units in 4 t Cz-DICz helps prevent undesirable molecular aggregation. The solution-processed OLEDs employing the CH-2D1 film, doped with 5 wt % 4 t Cz-DICz as the emitting layer, exhibited a deep-blue emission at 424 nm, characterized by a narrow bandwidth of 22 nm, and achieved a maximum external quantum efficiency (EQE) of approximately 4.0%. In contrast, the 4Hex-DICz-based device demonstrated an EQE of 2.91%. Consequently, we have successfully demonstrated that the introduction of four bulky t Cz units into the DICz core is a promising molecular design strategy for the development of soluble indolocarbazole-based emitters, especially those used in high-performance deep-blue fluorescent OLEDs.

Herein, a novel core molecule for V-shaped host molecules was synthesized, wherein two carbazoles were directly linked to cyclohexane. Cy-mCP and Cy-mCBP hosts were also successfully prepared for solution-processable thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The Cy-mCP and Cy-mCBP molecules contained a cyclohexane linker directly linked to two small molecular hosts (mCP and mCBP), exhibiting twice the molecular weight while maintaining the basic properties of a single host molecule with improved film-forming ability and solubility in organic solvents. These host materials showed superior thermal stability and high glass transition temperatures compared to lower molecular weight hosts. Green TADF-OLEDs were prepared using the two host materials and 2,4,5,6-tetra(3,6-di- tert -butylcarbazol-9-yl)-1,3-dicyanobenzene (t4CzIPN) emitter, achieving device efficiencies similar to that of a low-molecular-weight host. However, after the incorporation of a V-shaped host, superior characteristics were observed in terms of the thermal stability and operational stability of the device. The synthesis of V-shaped molecules by directly linking two carbazoles to a cyclohexane linker is promising for the development of different hosts for solution-processable OLEDs.

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- tert -butyl-9 H -carbazol-9-yl)-5-phenyl-5,12-dihydroindolo[3,2- a ]carbazole (tCzPhICz) and 12-(3,6-di- tert -butyl-9 H -carbazol-9-yl)-15 H -diindolo[2,3- b :1',2',3'- lm ]carbazole (tCzDICz) as bulky aryl-annulated [3,2- a ] carbazole donors, respectively. Both emitters showed sufficient solubility in organic solvents, narrow deep-blue emission, and small energy difference (Δ E ST ) between singlet and triplet states, which can be applied to solution-processable deep-blue TADF-OLEDs. Solution-processed OLEDs exploiting these TADF emitters displayed deep-blue electroluminescence with CIE y <0.1, and high external quantum efficiencies of 17.8 and 14.8% were observed for BO-tCzPhICz and BO-tCzDICz, respectively. The emitter bearing bulky ICz-based donating units shows highly promising potential for high-efficiency solution-processable deep-blue TADF-OLEDs.

Halogenated solvents are prevailingly used in the fabrication of nonfullerene organic solar cells (NF-OSCs) at the current stage, imposing significant restraints on their practical applications. By copolymerizing phthalimide or thieno[3,4- c ]pyrrole-4,6-dione (TPD) with 1,4-di(3-alkoxy-2-thienyl)-2,5-difluorophenylene (DOTFP), which features intramolecular noncovalent interactions, the backbone planarity of the resulting DOTFP-based polymers can be effectively tuned, yielding distinct solubilities, aggregation characters, and chain packing properties. Polymer DOTFP-PhI with a more twisted backbone showed a lower degree of aggregation in solution but an increased film crystallinity than polymer DOTFP-TPD. An organic thin-film transistor and NF-OSC based on DOTFP-PhI, processed with a nonhalogenated solvent, exhibited a high hole mobility up to 1.20 cm 2 V -1 s -1 and a promising power conversion efficiency up to 10.65%, respectively. The results demonstrate that DOTFP is a promising building block for constructing wide bandgap polymers and backbone coplanarity tuning is an effective strategy to develop high-performance organic semiconductors processable with a nonhalogenated solvent.

In this study, we synthesized two acceptor-donor-acceptor (A-D-A)-type small molecules (SMs) (P3T4-VCN and P3T4-INCN) with different terminal end-groups (dicyanovinyl (VCN) and 2-methylene-3-(1,1-dicyanomethylene)indanone (INCN)) based on the 1,4-bis(thiophenylphenylthiophene)-2,5-difluorophenylene (P3T4) core that possesses high coplanarity because of intrachain noncovalent Coulombic interactions. We investigated the influence of terminal end-groups on intermolecular packing and the resulting electrical and photovoltaic characteristics. A small change in the end-group structure of the SMs induces a significant variation in the torsional structures, molecular packing, and pristine/blend film morphology. It is noteworthy that the less crystalline P3T4-INCN with tilted conformation is highly sensitive to post-treatments (i.e., additives and annealing) such that it permits facile morphological modulation. However, the highly planar and crystalline P3T4-VCN exhibits a strong tolerance toward processing treatments. After morphology optimization, the fullerene-based bulk-heterojunction solar cell of tilted P3T4-INCN exhibits a power conversion efficiency (PCE) of 5.68%, which is significantly superior to that of P3T4-VCN:PC 71 BM (PCE = 1.29%). Our results demonstrate the importance of the terminal end-group for the design of A-D-A-type SMs and their sensitivity toward the postprocessing treatments in optimizing their performance.

A face-on oriented and p-doped semicrystalline conjugated polymer, poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole)] (PPDT2FBT), was studied as a hole-transport layer (HTL) in methylammonium lead triiodide-based perovskite solar cells (PVSCs). PPDT2FBT exhibits a mid-band gap (1.7 eV), high vertical hole mobility (7.3 × 10 -3 cm 2 /V·s), and well-aligned frontier energy levels with a perovskite layer for efficient charge transfer/transport, showing a maximum power conversion efficiency (PCE) of 16.8%. Upon doping the PPDT2FBT HTL with a nonhygroscopic Lewis acid, tris(pentafluorophenyl)borane (BCF, 2-6 wt %), the vertical conductivity was improved by a factor of approximately 2, and the resulting PCE was further improved up to 17.7%, which is higher than that of standard PVSCs with 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) as an HTL. After BCF doping, the clearly enhanced carrier diffusion coefficient, diffusion length, and lifetime were measured using intensity-modulated photocurrent and photovoltage spectroscopy. Furthermore, compared to the standard PVSCs with spiro-OMeTAD, the temporal device stability was remarkably improved, preserving the ∼60% of the original PCE for 500 h without encapsulation under light-soaking condition (1 sun AM 1.5G) at 85 °C and 85% humidity, which is mainly due to the highly crystalline conjugated backbone of PPDT2FBT and nonhygroscopic nature of BCF. In addition, formamidinium lead iodide/bromide (FAPbI 3-x Br x )-based PVSCs with the BCF-doped PPDT2FBT as an HTL was also prepared to show 18.8% PCE, suggesting a wide applicability of PPDT2FBT HTL for different types of PVSCs.