High-performance ternary organic solar cells with photoresponses beyond 1000 nm

Abstract

Panchromatic ternary organic solar cells with photoresponses beyond 1000 nm were fabricated using low-bandgap polymer PTB7-Th as a donor and ultralow-bandgap F8IC and mid-bandgap IDT-2BR as nonfullerene acceptors. A ternary device with 20% IDT-2BR content in acceptors exhibits a power conversion efficiency of 12.1%, higher than that of its parent binary devices based on PTB7-Th/F8IC (10.3%) and PTB7-Th/IDT-2BR (7.31%). The third component IDT-2BR simultaneously improves the open-circuit voltage (V_OC), short-circuit current density (J_SC) and fill factor (FF) of the PTB7-Th/F8IC blend. The voltage loss is reduced by the smaller energy offset for charge separation and new charge transport pathway for less charge recombination. Complementary light absorption is beneficial for enhanced J_SC. Co-existence of face-on molecular packing of F8IC and IDT-2BR leads to higher mobilities and more balanced charge transport, which contribute to the improved FF.