EDTA-2K Precursor Additive Strategy for Ambient-Air Processing of Inverted Inorganic Perovskite Solar Cells

Inverted inorganic perovskite solar cells are regarded as one of the most promising candidates for the top sub-cells in perovskite/silicon tandem solar cells. However, the rapid crystallization process and the interference of moisture and oxygen under ambient conditions tend to induce structural defects in inorganic perovskite films, thereby deteriorating device performance. To address the defect-related issues of inorganic perovskite films fabricated under ambient conditions, dipotassium ethylenediaminetetraacetate (EDTA-2K) was incorporated into the CsPbI₃ precursor solution. The additive regulates crystal growth through coordination interactions and simultaneously improves the interfacial contact between the perovskite layer and nickel oxide (NiO_x). The carboxylate groups in EDTA-2K can coordinate with undercoordinated Pb²⁺ species, thereby suppressing defect generation, while the nitrogen-containing sites strengthen interfacial coupling at the NiO_x/perovskite interface and mitigate non-radiative recombination losses. As a result, the treated films exhibit a reduced density of surface pinholes, enhanced crystallinity, and prolonged carrier lifetime. The trap-state density decreases from 1.23×10¹⁶ cm⁻³ to 1.08×10¹⁶ cm⁻³ after EDTA-2K modification. Based on this approach, inverted NiO_x-based inorganic perovskite solar cells fabricated in air achieve a power conversion efficiency (PCE) of 20.37%, together with excellent thermal, humidity, and light-soaking stability.