Optimizing CuSCN/photoactive interface towards efficient semitransparent organic solar cell with 55 % average visible transmittance

Developing highly-transparent organic solar cell (OSC) with an average visible transmittance (AVT) over 55 % and a reasonable light utilization efficiency (LUE) over 2.50 % is vital to enlarge its application scenarios for commercialization. Reducing electron-donor (D) content in photoactive layer represents a primary strategy for achieving this goal. However, the intrinsic transparent photoactive layer typically incurs exciton utilization penalty which requires the CuSCN in replacement of PEDOT:PSS to form an additional exciton splitting interface. Herein, we study the CuSCN-based OSC in the D-poor region for potential over 60 % AVT. Though CuSCN produces higher short-circuit current density (J_SC) than PEDOT:PSS as hole-transporting layer (HTL), the lower fill factor (FF) and its light-healing behavior suppress the power conversion efficiency (PCE) value. Detailed recombination analysis and Cu valence state comparison confirm the hole-trap at CuSCN/photoactive interface as the determinant reason for FF loss and its light-healing behavior. Targeted p-type doping close to the interface increases the FF in CuSCN-based PM6:L8-BO (0.10:1) OSC from 56.0 % to 62.1 % and mitigates the light-healing phenomenon as well as stability problem by hole-trap passivation. Taking advantage of the improved CuSCN device, a semitransparent OSC (ST-OSC) with an AVT exceeding 55 % and an appealing LUE of 2.66 % is fabricated.