Efficient ternary polymer solar cells with a parallel-linkage structure

Abstract

A series of ternary polymer solar cells (PSCs) were fabricated based on two narrow bandgap polymers PTB7 and PBDT-TS1 as the donors and PC₇₁BM as the acceptor. The performances of the ternary PSCs monotonically increased along with the PBDT-TS1 doping ratio, up to 80 wt% in the donors. The optimum power conversion efficiency (PCE) achieved for the ternary PSCs was 7.91% with an open circuit voltage (V_OC) of 0.76 V, a short circuit current density (J_SC) of 18.85 mA cm⁻² and a fill factor (FF) of 55.2% for the active layers with an 80 wt% PBDT-TS1 doping ratio in the donors. The optimized ternary PSCs show a 12.8% improvement compared to the optimum PCE of 7.01% for the binary PSCs with PBDT-TS1 as the donor and a 28.2% improvement compared with the optimum PCE of 6.17% for the binary PSCs with PTB7 as the donor. The FFs of all the ternary PSCs are larger than 54%, indicating efficient charge carrier transport channels in the ternary active layers. The energy or charge transfer between PTB7 and PBDT-TS1 should be neglected according to the investigation of the photoluminescence spectra of the blend films and the current density–voltage (J–V) curves of devices without the acceptor in the active layers. The ternary PSCs should be parallel-linkage structures with the donors independently working with the acceptor, which may be the most promising strategy for obtaining highly efficient ternary PSCs.