Asymmetric Non‐Fullerene Acceptors with Different Halogen Terminal Groups for Effective Passivation in Highly Efficient Inverted Perovskite Solar Cells

Interfacial challenges between the perovskite and electron transport layers severely limit the efficiency and stability of inverted (p-i-n) perovskite solar cells (PSCs). A simple and effective strategy to achieve desired perovskite layer is to find an effective passivator. Although non-fullerene acceptors have been applied to passivate defects in PSC, asymmetric organic molecules have rarely been explored. In this work, two asymmetric molecules SY1 and SY2 compared with symmetric molecule Y6, were introduced to optimize the properties of perovskite. It has been demonstrated that SY1, a molecule with a single chlorine atom on one side of its terminal groups, exhibits dominant face-on orientation with some degree of anisotropy and inferior crystallization, which facilitates the conjugated molecule entry into grain boundary leading to superior defect and grain boundary passivation properties. A certain presence of anisotropy contributes to reducing the residual stresses. In contrast, the stronger crystallization of Y6 and SY2 results in less effective passivation. Hence, a power conversion efficiency (PCE) of 25.63% was achieved for SY1-based device which is higher than SY2-based (24.12%) and Y6-based (24.70%) devices. These findings provide new insights into designing effective passivator molecules, helping to establish the correlation between their molecular structure and device performance.