Solubilizing Side Chain Engineering: Efficient Strategy to Improve the Photovoltaic Performance of Novel Benzodithiophene‐Based (X‐DADAD) n Conjugated Polymers

Triflic Acid-Assisted Regioselective Bromination of Quinoxaline Derivatives Enables a Facile Synthesis of Polymer PTQ10

Poly[(thiophene)-alt-(6,7-difluoro-2(2-hexyldecyloxy)quinoxaline)] (PTQ10) emerges as a promising candidate for donor materials in organic solar cells (OSCs) due to its high efficiency, simplified synthesis, and cost-effectiveness. The acceptor unit of PTQ10 is derived from the alkylation of 5,8-dibromo-6,7-difluoroquinoxaline-2-ol, emphasizing the importance of its economical synthesis for commercial viability. This study investigates triflic acid-assisted regioselective bromination of quinoxaline derivatives and proposes an alternative synthetic pathway for PTQ10. The developed route benefits from concise synthetic steps, a dependable procedure, and high overall yield. Starting with the condensation of 4,5-difluorobenzene-1,2-diamine with ethyl oxoacetate to yield 6,7-difluoroquinoxaline-2-ol, subsequent triflic acid-assisted regioselective bromination produces 5,8-dibromo-6,7-difluoroquinoxaline-2-ol in high yield. Alkylation under Mitsunobu reaction conditions yields 5,8-dibromo-6,7-difluoro-2-(2-hexyldecyloxy)quinoxaline, followed by polymerization with 2,5-distannylated thiophene under Stille reaction conditions to afford PTQ10. This research provides insights into efficient synthetic strategies for PTQ10, advancing its potential for commercial application in OSCs.

Remarkable Enhancement of Hole Mobility of Novel DA-D'-AD Small Molecules by Thermal Annealing: Effect of the D'-Bridge Block

Conjugated small molecules are advanced semiconductor materials with attractive physicochemical and optoelectronic properties enabling the development of next-generation electronic devices. The charge carrier mobility of small molecules strongly influences the efficiency of organic and hybrid electronics based on them. Herein, we report the synthesis of four novel small molecules and their investigation with regard to the impact of molecular structure and thermal treatment of films on charge carriers' mobility. The benzodithiophene-containing compounds (BDT) were shown to be more promising in terms of tuning the morphology upon thermal treatment. Impressive enhancement of hole mobilities by more than 50 times was found for annealed films based on a compound M4 comprising triisopropylsilyl-functionalized BDT core. The results provide a favorable experience and strategy for the rational design of state-of-the-art organic semiconductor materials (OSMs) and for improving their charge-transport characteristics.

Novel Push-Pull Benzodithiophene-Containing Polymers as Hole-Transport Materials for Efficient Perovskite Solar Cells

Donor-acceptor conjugated polymers are considered advanced semiconductor materials for the development of thin-film electronics. One of the most attractive families of polymeric semiconductors in terms of photovoltaic applications are benzodithiophene-based polymers owing to their highly tunable electronic and physicochemical properties, and readily scalable production. In this work, we report the synthesis of three novel push-pull benzodithiophene-based polymers with different side chains and their investigation as hole transport materials (HTM) in perovskite solar cells (PSCs). It is shown that polymer P3 that contains triisopropylsilyl side groups exhibits better film-forming ability that, along with high hole mobilities, results in increased characteristics of PSCs. Encouraging a power conversion efficiency (PCE) of 17.4% was achieved for P3-based PSCs that outperformed the efficiency of devices based on P1, P2, and benchmark PTAA polymer. These findings feature the great potential of benzodithiophene-based conjugated polymers as dopant-free HTMs for the fabrication of efficient perovskite solar cells.

Compatibility between Solubility and Enhanced Crystallinity of Benzotriazole-Based Small Molecular Acceptors with Less Bulky Alkyl Chains for Organic Solar Cells

Optimizing the molecular structures of organic solar cell (OSC) materials and boosting the power conversion efficiencies are the eternal theme in the solar energy region. A series of fused benzotriazole (BTA)-based A-DA'D-A structures of nonfullerene acceptors (such as Y18) were developed for application in efficient OSCs, in which high quantum efficiencies and low voltage losses could be achieved because of the optimized electron-deficient core and specific molecular geometry. Here, based on the BTA core, the bulky alkyl chain on the BTA unit was further tailored to minimize the lateral alkyl chains and enhance the crystallinity while maintaining an adequate solubility. The resulting NFAs of BTA-C1, BTA-C5, and BTA-C6 are synthesized. Compared with the well-designed molecular Y18 (BTA-C8), we found that simply replacing the 2-ethylhexyl chain with a single methyl (BTA-C1) can easily improve the fill factor up to 77%, but its poor light absorption capacity and large domain size impeded further efficiency improvement. In particular, the BTA-C5, with a shortened branch alkyl chain of 2-methylbutyl, achieves suitable solubility and enhanced crystallinity. Significantly, owing to the balanced charge carrier mobility and suitable phase separation, the BTA-C5-based binary single-junction OSCs achieve a high efficiency of 17.11%, which is one of the top values in BTA-based OSCs.