Central-Core Cycloalkane Modified Nonfullerene Acceptors Reduce Energy Loss for 20.2% Efficiency in Organic Solar Cells

Abstract

In recent years, power conversion efficiency (PCE) has exceeded 21% in organic solar cells (OSCs), thanks to the ongoing innovation of molecular design and device engineering. Among them, central-core engineering is a key strategy for optimizing nonfullerene acceptors (NFAs) to reduce energy loss and enhance charge transport in OSCs. In this work, two novel quinoxaline (Qx)-series NFAs, Qx-CHX and Qx-CP, are designed and synthesized by incorporating a rigid, nonaromatic cycloalkane (cyclohexane and cyclopentane) into the central core, respectively. The theoretical calculations and experiments indicate that, due to the smaller steric hindrance, a more planar molecular backbone, and better donor–acceptor miscibility, the D18:Qx-CP-based devices exhibit superior crystallinity and optimal phase separation, delivering a champion PCE of 18.75% with a low energy loss of 0.48 eV. In comparison, the Qx-CHX-based devices achieve a higher open-circuit voltage (V_OC) of 0.905 V and a PCE of 18.02%. Notably, using Qx-CP as a guest acceptor in the D18:BTP-eC9 system further boosts the PCE to 20.25% with significantly enhanced short-circuit current (J_SC) and fill factor (FF). This work highlights central-core modification as an effective approach for high-performance OSCs.