Two polymers based on thiophene-dione derivatives, PhEH-T and PhBO-T, have been designed and synthesized as donor polymers for polymer solar cells (PSCs), adopting an electron donor (D)–electron acceptor (A) architecture. Alkoxy-substituted benzylidene cyclopenta[c]thiophene-dione units, bearing 2-ethylhexyloxy (PhEH-T) or 2-butyloctyloxy (PhBO-T) side chains, serve as the electron acceptor units, while fluorinated benzodithiophene (BDTF) serves as the electron donor unit. The alkoxy chain exhibits electron-donating character owing to its conjugation, with extended chains enhancing solubility, while the π-bridge unit further tunes donor-acceptor interactions and backbone electronic properties. Inverted-type non-fullerene PSCs (ITO/ZnO/polymer:Y6-BO/MoO3/Ag) were fabricated to evaluate photovoltaic performance. The PhEH-T-based device, benefiting from the strong electron-donating character of its alkoxy group, achieved a power conversion efficiency (PCE) of 4.05%, whereas extending the alkyl chain in PhBO-T yielded a fill factor (FF) of 46.9% and the highest PCE of 7.45%. This gap is consistent with the limited molecular weight and narrower molecular weight distribution of PhEH-T, together with weaker donor-acceptor miscibility, whereas the extended alkoxy chain of PhBO-T simultaneously increases molecular weight and its distribution, improves blend miscibility, and promotes a more well-ordered structure. Notably, although the deeper HOMO level of PhBO-T would be expected to raise the open-circuit voltage (Voc), this shift corresponds to only a modest increase, from 0.72 V to 0.75 V, indicating that HOMO-level modulation alone does not govern performance. The larger gains of PhBO-T appear instead in short circuit current density (Jsc) and FF, pointing to processability-related factors, namely solubility-driven molecular weight, blend miscibility and molecular ordering, rather than energy-level tuning as the more effective handle in this thiophene-bridged platform. Since these factors change together with alkoxy chain length, their individual contributions cannot be separated in this study.
Organic solar cells (OSCs) have witnessed continuous efficiency advancement enabled by self-assembled monolayer (SAM) hole-transport layers. However, such ultrathin SAM films are vulnerable to chloroform erosion during active-layer spin-coating, which may induce partial monolayer detachment and poor device reproducibility. Herein, we report a poly(carbazole phosphonic acid) polymeric material termed Poly-4PADCB, which features multidentate phosphonic anchoring sites and an extended conjugated backbone. Benefiting from cooperative multipoint interfacial binding with the indium tin oxide (ITO) substrate, Poly-4PADCB exhibits improved tolerance toward chloroform rinsing. Moreover, this polymer delivers favorable thickness-insensitive characteristics compared with conventional SAMs, retaining competitive photovoltaic performance within a thickness range of 1-20 nm. OSCs adopting Poly-4PADCB as the hole-transport layer (HTL) yield a peak power conversion efficiency (PCE) of 17.7% at an active area of 0.063 cm2. The unencapsulated devices maintain about 90% of the initial PCE after 1400 h ambient storage, and retain over 60% of their initial efficiency after 500 h of continuous full-spectrum solar-lamp illumination.
Establishing reliable structure–processability relationships is essential for advancing organic solar cells (OSCs) toward scalable manufacturing. Herein, we present a comparative study of donor–acceptor (D–A) copolymers incorporating thiophene (T) and thienothiophene (TT) donor units, examining how donor and acceptor structure, polymerization outcome, molecular weight, operational solubility, and processing conditions are associated with film formation and device reproducibility under ambient blade-coating conditions. Six donor–acceptor copolymers (seven samples, including a TT3 batch prepared with a shorter reaction time, TT3*) were synthesized via Stille coupling and characterized with respect to molecular structure, molecular weight distribution, optoelectronic properties, thermal stability, thin-film morphology, and photovoltaic performance. TT-containing polymers showed distinct optical and processing behavior, but the present data do not isolate backbone conformation as the sole origin of these differences. Only the thiophene-based polymers T1, T2, and T3 could be processed into devices; among them, only T3 combined a high estimated degree of polymerization (DPn ≈ 25) with good film-forming ability, whereas T1 and T2 were obtained as short-chain materials (DPn ≈ 6). Among the investigated materials, T3 delivered the most reproducible device performance, reaching a power conversion efficiency of 2.69% in large-area (0.55 cm2) flexible OSCs. Rather than establishing a single causal relationship between backbone structure and device efficiency, this study highlights the combined importance of molecular structure, attainable molecular weight, solution processability, and processing tolerance for scalable ambient fabrication.
In this work, three thermally activated delayed fluorescence (TADF) materials with the same DMAC core, namely DMAC-TRZ, DMAC-MPM and DMAC-DPS, were employed as donors to construct exciplex organic light-emitting diodes (OLEDs) with acceptor 3P-T2T. The exciplex OLEDs based DMAC-TRZ: 3P-T2T achieved the best performance, delivering a maximum luminance of 34740 cd/m2, current efficiency of 36.8 cd/A, power efficiency of 33.6 lm/W and external quantum efficiency of 11.5%, respectively. Interestingly, all three devices showed similar efficiency levels, indicating that the DMAC donor unit in the TADF materials plays a major role in forming high efficiency exciplex, rather than the overall molecular structure of TADF donor. The high efficiency of DMAC-core donor: 3P-T2T exciplex systems is attributed to dual reverse intersystem crossing (RISC) process, the intrinsic RISC of the TADF donor together with the RISC of the exciplex, which significantly enhances triplet exciton utilization. Furthermore, warm white OLEDs were successfully fabricated by doping Rubrene/DCJTB emitters into the DMAC-TRZ: 3P-T2T exciplex host, respectively. This work demonstrated the effect of donor molecular structure on the performance of exciplex, which provided a feasible strategy for designing heavy-metal-free, low-cost and high efficiency exciplex OLEDs.
