Polymer Modification on the NiOx Hole Transport Layer Boosts Open-Circuit Voltage to 1.19 V for Perovskite Solar Cells

Inverted-structure perovskite solar cells (PVSCs) applying NiOx as the hole transport layer (HTL) have attracted increasing attention. It is still a challenge to optimize the contact between NiOx and the perovskite layer and to suppress energy loss at the interface. In this study, interface engineering was carried out by modifying the NiOx layer with different polymers such as polystyrene, poly(methyl methacrylate) (PMMA), or poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) to improve the surface contact between NiOx and the perovskite, to decrease the defect states, and to make the energy level alignment better. The NiOx/PMMA-based device presents a Voc as high as 1.19 V because of the improved interfacial contact and the interaction of the carbonyl and methoxy group with Pb2+. The NiOx/PTAA-based device with the structure ITO/NiOx/PTAA/(MAPbI3)0.95(MAPbBr2Cl)0.05/PCBM/BCP/Ag exhibits the highest power conversion efficiency of 21.56% with a high Voc of 1.19 V. The enhanced performance can be attributed to the deepened highest occupied molecular orbital level of NiOx/PTAA, which matched well with that of the perovskite and suppressed interface energy loss as well. This work provides a facile approach for efficiently improving the Voc of NiOx-based PVSCs.