High-Efficiency Nonfullerene Organic Solar Cells Enabled by 1000 nm Thick Active Layers with a Low Trap-State Density

The high-efficiency organic solar cells (OSCs) with thicker active layers are potential candidates for the fabrication of large-area solar panels. The low charge carrier mobility of the photoactive materials has been identified as the major problem hindering the photovoltaic performance of the thick-film OSCs. In this study, high performance of ultra-thick-film OSCs employing a nonfullerene acceptor BTP-4Cl and a polymer donor PBDB-TF is demonstrated. Two blends (PBDB-TF:BTP-4Cl and PBDB-TF:IT-4F) show comparable mobilities and excellent photovoltaic characteristics in thin-film devices, while in the 1000 nm thick devices, although they both exhibit desirable and balanced mobilities, the PBDB-TF:BTP-4Cl-based blend possesses lower trap-state density than the IT-4F-based counterpart, leading to lower trap-assist recombination, longer carrier lifetime, and thus a much higher short-circuit current density in the device. As a result, the BTP-4Cl-based 1000 nm thick OSC achieves a remarkable power conversion efficiency of 12.1%, which greatly outperforms the IT-4F-based devices (4.72%). Furthermore, for a 1000 nm thick device with an active area of 4 cm², a promising efficiency of 10.1% was obtained, showing its great potential in future large-scale production.