Novel In Situ Self-Doping Cathode Interlayer Materials with Thickness-Insensitivity for High-Efficiency Organic Solar Cells

With the power conversion efficiency (PCE) of single junction organic solar cells (OSCs) surpassing 19%, the development of active layer materials and interlayer materials with thickness-insensitive character becomes crucial for large-area device fabrication. In this study, we synthesized two in situ self-doping cathode interlayer materials, namely PBDPN-Br and PBDPVN-Br, via aldol polycondensation. Compared with PBDPN-Br, PBDPVN-Br, which incorporates ethylene bonds, exhibits enhanced planarity of the conjugated backbone, resulting in improved electron transport capability. When employed as a cathode interlayer in OSCs based on PM6:EH-HD4F, PBDPN-Br and PBDPVN-Br achieved PCEs of 17.59 and 17.89%, respectively. Notably, the PBDPVN-Br-based devices could retain 93% of the initial PCE even though the interlayer thickness was increased to 50 nm, while only 82% of the initial PCE could be retained for PBDPN-Br (50 nm)-based devices. These results highlight the success of regulating the planarity of conjugated backbones for the development of effective thickness-insensitive cathode interlayer materials. Furthermore, when PBDPVN-Br was utilized in OSCs based on the D18:BTP-eC9 active layer, a champion PCE of 18.44% could be achieved, underscoring its competitiveness as a cathode interface material for large-scale processed OSCs.