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

Inverted-structure perovskite solar cells (PVSCs) applying NiO as the hole transport layer (HTL) have attracted increasing attention. It is still a challenge to optimize the contact between NiO and the perovskite layer and to suppress energy loss at the interface. In this study, interface engineering was carried out by modifying the NiO 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 NiO and the perovskite, to decrease the defect states, and to make the energy level alignment better. The NiO/PMMA-based device presents a V_oc as high as 1.19 V because of the improved interfacial contact and the interaction of the carbonyl and methoxy group with Pb²⁺. The NiO/PTAA-based device with the structure ITO/NiO/PTAA/(MAPbI₃)_0.95(MAPbBr₂Cl)_0.05/PCBM/BCP/Ag exhibits the highest power conversion efficiency of 21.56% with a high V_oc of 1.19 V. The enhanced performance can be attributed to the deepened highest occupied molecular orbital level of NiO/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 V_oc of NiO-based PVSCs.