Improving the Performance of Ternary Organic Solar Cells via Optimizing Molecular Orientation and 3D Charge Transport

Abstract Recently, through in‐depth investigations of ternary organic solar cells (OSCs), scientists have discovered that small molecules (SMs) with edge‐on orientation serving as the third component can boost transverse charge transport and consequently enhance device performance. Nevertheless, little research has been conducted on determining how to select an appropriate third component to improve 3D charge transport. Herein, four SMs are designed by gradually increasing the quantity of alkyl thiophene as an π‐bridge to adjust their crystallinity and orientation. The resulting SMs show similar edge‐on orientation but different crystalline degrees, due to the complex effects of molecular steric hindrance and extended conjugation. After the introduction of SMs, most of the ternary devices exhibited a pronounced improvement in power conversion efficiencies (PCEs) than the control binary counterparts. An elegant PCE of 19.02% and a fill factor approaching 80% are collected in the ternary OSCs. A balanced 3D charge transport bimodal mechanism is proposed and effectively elucidated in the ternary blend film, enabling charges to bypass the interfering domains and thereby improve the device performance. This research provides guidance for the development of SM third components to form 3D percolation paths that facilitate charge transport and subsequently enhance the performance of ternary devices.