Improved Stability and Efficiency of Inverted Perovskite Solar Cell by Employing Nickel Oxide Hole Transporting Material Containing Ammonium Salt Stabilizer

Abstract Nickel oxide (NiO) is one of the promising hole‐transporting materials for perovskite solar cells (PSCs). Despite the ongoing efforts to improve PSC performance with sol–gel NiO, there has been limited study on the usage and influences of stabilizers on NiO and the relevant performance of PSCs. Until now, most of the sol–gel NiO methods use chemical stabilizers based on strongly acidic or mild basic catalysts such as hydrochloric acid and monoethanolamine. However, it is evident that the remaining pH‐biased stabilizers in the film aggravate device stability. Therefore, it is imperative to develop a more stable and effective NiO, which can boost the performance of PSC. Here, the relatively neutral ammonium salt is utilized in NiO solution, which can improve the hole transport capability and stability of NiO. Under the optimum salt condition, energy level and hole conductivity are modulated favorably for hole transportation. Moreover, constructive interaction between the ammonium salt and perovskite enhances interfacial properties and reduces trap‐assisted recombination. Based on this novel NiO, the champion power conversion efficiency of 19.91% with an exceptionally high open‐circuit voltage of 1.13 V among the reported MAPbI 3 ‐based PSCs is demonstrated. Furthermore, NiO with salt stabilizer secures long‐term device stability, maintaining 97% of initial power conversion efficiency (PCE) even after 800 h.