Carboxyl functional group-assisted defects passivation strategy for efficient air-processed perovskite solar cells with excellent ambient stability

Because the perovskites materials tend to decompose in humid air and at high temperature, a controlled inert condition is usually necessary to obtain high-performance perovskite solar cells (PSCs), which is inconvenient for large-scale commercial production. Furthermore, defects/traps in the perovskite layer, as non-radiative charge recombination centers, dramatically deteriorate the device efficiency and stability. Inspired by the Lewis acid-base adduct theory, herein we report a terephthalic acid (PTA)-assisted defect passivation strategy for fabricating highly efficient and stable devices in ambient air. Density functional theory calculation confirms that electrons are located at two carboxylic acid end groups in the PTA molecule, which can serve as Lewis base to form the Lewis acid-base adduct with uncoordinated Pb2+ defects. The PTA-treatment effects promote high performance of PSCs, the champion device provides power conversion efficiency (PCE) of 18.22%, in sharp contrast to 17.41% of control sample. More importantly, unencapsulated devices retain over 80% of their original PCE after being stored for 4500 h in air (≈45% average relative humidity (RH)), exhibiting one of the best long-term stability to date. Correspondingly, PTA-treatment gives the device favorable thermal stability. Our strategy provides a simple yet effective path for passivating defects and improving performance of PSCs.