19.35% Efficient Binary Bulk-Heterojunction Organic Photovoltaic Enabled by Optimizing Bromine-Substituted Self-Assembled Carbazole Based Molecules

A bromine-substituted [2-(9H-Carbazol-9-yl) ethyl] phosphonic acid, 1Br-2PACz, is designed as hole-selective self-assembled monolayers (SAMs), contributing to an outstanding power conversion efficiency (PCE) of 19.35% for binary bulk-heterojunction (BHJ) based organic solar cells (OSCs). As compared to the previous high-performance 2Br-2PACz SAMs, 1Br-2PACz molecules can effectively reduce the interaction of the SAM with the BTP-eC9 nonfullerene acceptors with a decreased binding energy, resulting in the suppressed vertical self-aggregation of BTP-eC9 small molecules as the bottom side of PM6:BTP-eC9 BHJ during the solidification process. There is decreased energetic disorder within photoactive layer together with more efficient charge transfer and suppressed non-radiative recombination. Furthermore, five additional binary BHJ systems are applied in 1Br-2PACz SAM-based OSCs, exhibiting continuously superior performance as compared to the reference cells with conventional PEDOT:PSS hole transport layer. This work underscores the potential of advancing OSCs by fine-tuning SAMs through halogenation strategies to improve active layer morphology and overall device performance.