Ternary polymer solar cells with alloyed donor achieving 14.13% efficiency and 78.4% fill factor

Highlights: • The optimized ternary PSCs with alloyed donor achieve a PCE of 14.13% and a FF of 78.4%. • Over 11% PCE improvement is obtained by employing ternary strategy based on binary PSCs with efficiency more than 12%. • The simultaneously increased J_SC and FF can well compensate the slight V_OC loss in the optimized ternary PSCs. -- Abstract: The power conversion efficiency (PCE) reaches to 12.63% or 12.19% for polymer solar cells (PSCs) based on PM6 or J71 as donor and Br-ITIC as acceptor, respectively. A series of ternary PSCs with two donors were fabricated by combining the merits of the two binary PSCs. The PM6 and J71 prefer to form alloyed donor due to the good compatibility, which is beneficial to finely optimize photon harvesting and phase separation of ternary active layers, leading to simultaneous improvement of short-circuit current density (J_SC) and fill factor (FF). The improved J_SC and FF can well make up for the slight loss of open-circuit voltage (V_OC). The optimized ternary PSCs with 20 wt% J71 in donors achieve a PCE of 14.13% and a FF of 78.4%. More than 11% PCE improvement is achieved by adopting ternary strategy on the basis of two binary PSCs with PCE over 12%, also keeping simple fabrication technology.