A fluorine functionalised phosphine based solid additive for morphology control and achieving efficient organic solar cells

Fine-tuning of the morphology of the bulk heterojunction (BHJ) active layer at the nanoscale plays an essential role in realising the full potential of the performance of organic photovoltaic (OPV) devices. Among many approaches, solid additive engineering has been identified as the most effective way to control the nanostructure of interpenetrating donor-acceptor domains in the photoactive layer for efficient charge separation and transport. In this work, we employed tris(pentafluorophenyl)phosphine as a solid additive (TPFPP) to modulate the donor-acceptor phase separated morphology of a photoactive layer based on a semiconducting polymer (PM6) and a non-fullerene acceptor (BTP-eC9). The fluorine bonding interaction between the additive and photoactive materials, and the volatilisation of the solid additive upon thermal annealing, from the photoactive layer induces the BHJ nanostructure rearrangement, leading to larger crystalline sizes and better charge separation and transport properties in devices. With an optimum concentration of the solid additive, the power conversion efficiency (PCE) of OPV devices based on the PM6:BTP-eC9 photoactive layer significantly increases from 15.1% to 16.9%. These findings indicate that the phosphine-based solid additive (TPFPP) can be an efficient and simple way to enhance the device performance, demonstrating a multifunctional solid additive for the fabrication of efficient OPV devices.