Cross-Linking-Integrated\nSequential Deposition: A\nMethod for Efficient and Reproducible Bulk Heterojunctions in Organic\nSolar Cells

The formation of bulk heterojunctions (BHJs) through\nsequential\ndeposition (SqD) of polymer donor and nonfullerene acceptor (NFA)\nsolutions offers advantages over the widely used single-step deposition\nof polymer:NFA blend solutions (BSD). To enhance the application of\nSqD in organic solar cell production, it is crucial to improve reproducibility\nand stability while maintaining a high efficiency. This study introduces\na novel method termed cross-linking-integrated sequential deposition\n(XSqD) for fabricating efficient and reproducible BHJs. In this method,\npolymers are cross-linked using efficient 2Bx-4EO or 2Bx-8EO cross-linkers,\nwhich enhance the solvent resistance of the polymer donor layer against\nthe solvents used for NFAs. This approach addresses the challenge\nof selecting a suitable solvent for NFAs, a major obstacle in SqD-processed\nOSCs. The utilization of 2Bx-4EO in XSqD leads to a significant increase\nin reproducibility compared to that of conventional SqD, coupled with\na high-power conversion efficiency (PCE) of 14.1%. Furthermore, XSqD\ndevices exhibit superior stability, showing only 1% and 6% reductions\nin their initial PCE after thermal stress at 80 and 120 °C for\n50 h, respectively.