Surface modification of perovskite film by an amino acid derivative for perovskite solar cell

Perovskite solar cell (PSC) is an emerging photovoltaic device with high performance, but defects from surface of perovskite film seriously limit its further development and even lead to performance degradation. In this paper, a functional derivative of amino acid, N-(9-Fluorenylmethoxycarbonyl)-l-leucine (Fmoc-Leu-OH), containing benzene ring, CO, -NH-, and –COOH is introduced to passivate surface defects at perovskite layer. We have found that the amino acid derivative can partly participate in the crystallization process of perovskite, which is beneficial to eliminate PbI2 impurity and reduce surface defect of the perovskite film. As a result, these advantages strengthen the carrier interface transport property and improve photovoltaic performance and long-term stability of corresponding PSCs. Compared to the pristine PSC, the derivative modified device could raise the efficiency from 13.33% to 15.59% with the open circuit voltage (Voc) increased from 1.01 V to 1.05 V. Moreover, the unpackaged PSC with amino acid derivative could maintain an initial efficiency of more than 77% after 240 h and a stable output current of 18.53 mA cm−2 for 300 s, exhibiting an excellent environmental stability.