D18/Y7 Pseudo-bilayer organic solar cells: effect of donor concentration tuning

Layer-by-layer (LBL) solution processing in organic solar cells (OSCs) is an effective strategy for controlling active-layer composition and charge-transport pathways compared with bulk-heterojunction devices. Sequential deposition of donor and acceptor layers in the LBL process has led to a remarkable improvement in power conversion efficiency ( PCE ). Here, we report an optimized bilayer OSC fabricated via LBL deposition strategy, based on the polymer donor D18 and the non-fullerene acceptor Y7, achieving a PCE of 15.7%. The systematically varied donor concentration influences active-layer thickness optimization, as evidenced by the photovoltaic parameters. This study provides insights into how variations in donor concentration influence key photovoltaic parameters and highlights its critical role in optimizing charge carrier generation and transport. The increased long-term stability and performance of our optimized devices under prolonged aging provide further perspectives to bilayer OSCs.