Functional design and understanding of effective additives for achieving high-quality perovskite films and passivating surface defects

Achieving high-quality perovskite films without surface defects is regarded as a crucial target for the development of durable high-performance perovskite solar cells. Additive engineering is commonly employed to simultaneously control the growth of perovskite crystals and passivate defects. Here, 4-(trifluoromethyl)benzoic anhydride (4-TBA) composed of benzene rings functionalized with carbonyl and trifluoromethyl groups was used as an example additive to study the characteristics of additives used for producing high-quality perovskites and controlling their surface properties. The interaction between 4-TBA and perovskite precursor materials was investigated using density functional theory (DFT) simulations. The electron-rich carbonyl group efficiently passivated the under-coordinated lead-ion defects. Additionally, hydrogen bonding between trifluoromethyl and organic cations prevents the generation of cation vacancies. Because of its intrinsic hydrophobicity, the trifluoromethyl group simultaneously improves the moisture and heat stability of the film. 4-TBA serves as a universal modifier for various perovskite compositions. The power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) based on methylammonium (MA) with 4-TBA was improved from 16.15% to 19.28%. Similarly, the PCE of inverted PSCs based on a cesium formamidinium MA (CsFAMA) perovskite film increased from 20.72% to 23.58%, upon addition of 4-TBA. Furthermore, the moisture and thermal stability of 4-TBA-treated films and devices was significantly enhanced, along with prolonged device performance. Our work provides guidance on selecting the structure and functional groups that are essential for surface defect passivation and the production of high-quality perovskites.