NiO Hole Transport Layer for Perovskite Solar Cells with Improved Stability and Reproducibility

In this study, highly stable, low-temperature-processed planar lead halide perovskite (MAPbI_3- Cl ) solar cells with NiO interfaces have been developed. Our solar cells maintain over 85% of the initial efficiency for more than 670 h, at the maximum power point tracking (MPPT) under 1 sun illumination (no UV-light filtering) at 30 °C, and over 73% of the initial efficiency for more than 1000 h, at the accelerating aging test (85 °C) under the same MPPT condition. Storing the encapsulated devices at 85 °C in dark over 1000 h revealed no performance degradation. The key factor for the prolonged lifetime of the devices was the sputter-deposited polycrystalline NiO hole transport layer (HTL). We observed that the properties of NiO are dependent on its composition. At a higher Ni³⁺/Ni²⁺ ratio, the conductivity of NiO is higher, but at the expense of optical transmittance. We obtained the highest power conversion efficiency of 15.2% at the optimized NiO condition. The sputtered NiO films were used to fabricate solar cells without annealing or any other treatments. The device stability enhanced significantly compared to that of the devices with PEDOT:PSS HTL. We clearly demonstrated that the illumination-induced degradation depends heavily on the nature of the HTL in the inverted perovskite solar cells (PVSCs). The sputtered NiO HTL can be a good candidate to solve stability problems in the lead halide PVSCs.