Room-temperature and solution-processed copper iodide as the hole transport layer for inverted planar perovskite solar cells

Inverted planar heterojunction perovskite solar cells with poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) sulfonic acid (PEDOT:PSS) as the hole transport layer (HTL) have attracted significant attention during recent years. However, these devices suffer from a serious stability issue due to the acidic and hygroscopic characteristics of PEDOT:PSS. In this work, we demonstrate a room-temperature and solution-processed CuI film which is used as the HTL for inverted perovskite solar cells. As a result, an impressive PCE of 16.8% is achieved by the device based on the CuI HTL. Moreover, the unsealed CuI-based device displays enhanced air stability compared to the PEDOT:PSS-based device. In addition, the fabrication of the CuI HTL is a simple and time-saving procedure without any post-treatment, thus making it a promising candidate as the HTL in inverted perovskite solar cells and a potential target for efficient flexible and tandem solar cells.