Achieving 19.78%‐Efficiency Organic Solar Cells by 2D/1A Ternary Blend Strategy with Reduced Non‐Radiative Energy Loss

Abstract Reducing non‐radiative energy loss (∆ E nr ) is critical for enhancing the photovoltaic performance of organic solar cells (OSCs). To achieve this, a small molecular donor, LJ1, is introduced as the third component in the host system D: A system (D18: BTP‐eC9‐4F). The cascade‐like energy level alignment of D18, LJ1, and BTP‐eC9‐4F facilitates efficient charge transfer. LJ1's good solubility in the processing solvent and high miscibility with BTP‐eC9‐4F delay the precipitation of BTP‐eC9‐4F, leading to improved phase morphology in blend films. Additionally, LJ1 increases spacing between the polymer donor (PD) and the small molecule acceptor (SMA), optimizing blend film morphology and reducing non‐radiative energy loss in OSCs. Ternary OSCs based on D18:LJ1:BTP‐eC9‐4F achieve a power conversion efficiency (PCE) of 19.43% with reduced ∆ E nr . Notably, the ternary device using D18:LJ1:L8‐BO attains an outstanding PCE of 19.78%, which is one of the highest device efficiency for ternary OSC. The work highlights the effectiveness of the ternary blend strategy in enhancing OSC performance while minimizing ∆ E nr .