Efficient Perovskite Solar Cells with a CuI-Modified Polymer Hole-Transport Layer

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) is one of the most used polymer hole-transport layers in inverted perovskite solar cells (PVSCs). However, due to the poor crystal quality of perovskite films prepared on the PTAA underlayer, the solar cells with the PTAA hole-transport layer have not shown excellent photoelectric performance. Furthermore, as a polymer semiconductor material, PTAA is highly hydrophobic, and the wettability of the perovskite precursor solution on the surface of PTAA is not very good, affecting the crystal quality of the perovskite film. CuI has not only a suitable energy-level structure and excellent charge transfer efficiency but also the same element iodine as perovskite, which is conducive to the formation of good interface contact. In this paper, a PTAA film is modified with CuI, which not only improves the wettability but also promotes the crystallization of the perovskite film. A method is developed to estimate the deep defect density from transient open-circuit voltage decay. Using this method, we compare the density of deep-level traps of the perovskite active layer on a CuI-modified PTAA film with that on a PTAA film. We demonstrate that CuI modification to PTAA can inhibit both shallow defects and deep defects, which facilitates carrier transport effectively. The power conversion efficiency (PCE) of the CuI-modified devices achieves 20.20%, which is significantly higher than the 18.07% of the PTAA-only devices. This study demonstrates that the inorganic semiconductor material CuI-modified polymer hole-transport layer is an approach that would provide guidance for interface modification engineering of PVSCs.