Chelating Agent Mediated Sol–Gel Synthesis for Efficient Hole Extracted Perovskite Photovoltaics

Ethylenediamine (EDA, amine-based Lewis base) was utilized as a base catalyst in the synthesis of nickel oxide (NiOx) to regulate the coordination properties of metal ions (Lewis acid). The effect of the EDA chelating agent on the hole transporting properties of NiOx was determined according to crystal field theory. The particle size in the NiOx thin film changed according to the EDA molar ratio, which influenced the electrical properties and affinity with the photoactive layer. Excellent electrical conductivity and improved crystallinity of the perovskite layer were confirmed via a conductive atomic force microscope (C-AFM), X-ray diffraction (XRD), and field emission scanning electron microscope (FE-SEM) analyses at the optimal EDA ratio in NiOx. In particular, UPS (reduced energy band offset) and charge dynamics data demonstrate the enhanced short circuit current, fill factor, and efficiency of the perovskite solar cells. Comprehensively, this study supports the role and effect of the EDA chelating agent in NiOx for next-generation solar cells. Moreover, it provides insight into the understanding and potential of various sol–gel materials synthesized based on crystal field theory.