A high-efficiency and stable organic solar cell with balanced crystallization kinetics

Abstract

Obtaining controllable morphology in organic solar cells (OSCs) has long been sought to improve the photovoltaic efficiency and long-term stability for meaningful applications. Herein, we report a conceptual multiple acceptor OSC based on co-acceptor guests. Through monitoring the solution phase to solid-state film transition of the multi-acceptor based bulk heterojunctions (BHJs) by in situ optical spectroscopy, we show that the introduced co-acceptor guests featuring opposite crystallization trends are highly beneficial for attaining synergies in balancing the crystallization kinetics and modifying phase separation and charge carrier transport behaviors. Our combined investigation with GIWAXS, solid-state NMR, depth-sensitive optical spectroscopy and transient opto-electrical measurements further reveals the central functionality of the co-acceptor guests in leveraging and optimizing the crystallization dynamics and vertical phase separation while maintaining the favored short-range structural order. Based on a multi-acceptor model system, PM6:BTP-eC9:Y6-1O:PC₇₁BM, we achieved a champion power conversion efficiency (PCE) of 19.35%, showing impressive photostability with the PCE decaying by <20% after ∼30 days of continuous irradiation. The demonstrated multi-component approach provides a valuable opportunity for fine optimization of the phase morphology and long-term device stability in OSCs toward realistic energy conversion applications.