Regulating Förster resonance energy transfer and cascade energy offset achieves 19.6% efficiency in ternary organic solar cells

Abstract

The short-circuit current density (J_SC) is a critical factor in enhancing organic solar cell performance (OSCs). However, an increase in J_SC is often associated with a reduction in open circuit voltage (V_OC), limiting the development of OSCs. Herein, a wide bandgap nonfullerene acceptor (NFA), which serves as a Förster resonance energy transfer (FRET) donor, was incorporated into the active layer to improve the J_SC without sacrificing the V_OC. When IDIC was added to the host D18-Cl:Y6, the photoluminescence quenching efficiency increased from 95.1% to 98.7%. In combination with the FRET from IDIC to Y6, due to the IDIC emission and Y6 absorption spectra overlap, the ternary devices attained a remarkable J_SC of 29.28 mA cm⁻², and an optimum power conversion efficiency (PCE) of 19.67%, with a V_OC of 0.866 V, which is the same as the V_OC in control devices. Additionally, inverted OSCs with laminated ternary active layers exhibited a PCE of 17.85%, outperforming their inverted binary counterparts. Besides FRET, the cascade energy alignment reduces the hole extraction barrier, facilitating the charge transfer processes. The findings on the impact of IDIC on the performance of OSCs provide guidelines for designing novel materials for developing high-performance ternary OSCs.