Performance enhancement of inverted perovskite solar cells through lithium-ion diffusion from the nickel oxide hole transport layer to the perovskite absorber

Inverted perovskite solar cells, known for their low temperature processability and reduced hysteresis, benefit from the use of nickel oxide (NiO_x) as a hole transport material, which enhances stability. The doping of NiO_xwith lithium improves its electrical properties by creating Ni³⁺sites through intrinsic doping with Ni vacancies. This study investigated the impact of Li doping on the optical and electrical properties of NiO_xand evaluated the optimal doping concentration for solar cell performance. Additionally, the diffusion of small sized Li-ions from the NiO_xhole transport layer into the photoactive perovskite layer was investigated, which led to an improvement of the perovskite absorber quality through defect passivation caused by lithium diffusion from the NiO_xlayer, enhancing device performance. The incorporation of lithium significantly boosted all solar cell parameters, leading to a 60.8% increase in power conversion efficiency (PCE), from approximately 12% to a maximum of 19.3%.