4-Carboxyphenyl isothiocyanate as a Lewis base additive for efficient and stable perovskite solar cells

A high-quality perovskite film is of great significance for efficient and stable perovskite solar cells (PSCs). The use of additives to improve the crystallinity and morphology of perovskite films is an effective way to improve the performance of PSC devices. In this work, 4-carboxyphenyl isothiocyanate (CPIC) was used as an additive in perovskite films to improve the quality of the films. The results of FT-IR showed that the SCN- and-COOH groups with Lewis base in CPIC can coordinate with unpaired Pb2+ on the perovskite films to form Lewis acid-base adducts. The addition of CPIC can effectively improve the crystallinity and grain size of the perovskite films. The results showed that the short circuit current density (JSC) and fill factor (FF) of PSC devices increase significantly with the improvement of film quality, when the concentration of CPIC is 0.5 mg mL-1. These made the efficiency of the devices increase from 16.16 % to 18.19 %. Meanwhile, the introduction of the benzene ring in CPIC can improve the stability of the PSC devices. After aging at room temperature and 50 % humidity for 30 days, the device added with CPIC retained 61.9 % of the initial PCE. This work proves that using CPIC as an additive is an effective method to achieve efficient and stable PSCs.