Probing the Impact of Ionic Liquid Additives at the Buried NiO_x/Perovskite Interfaces to Understand Solar Cell Performance

The buried interfaces between charge-selective contacts and metal halide perovskites are critical to photovoltaic device performance, and as such, a number of additives are proposed to control and modify energy level alignment. Interface engineering strategies ultimately require the successful detection of near-band energetics as well as the assessment of charge transport processes, including injection and/or extraction barriers under relevant electric fields. Herein, the study utilizes a low-cost, straightforward electroabsorption approach for operando characterization of buried interfaces of NiO_x hole-selective layers/metal halide perovskite photoactive layers, complemented with full solar cell device performance. The spectroelectrochemical approach is used to quickly optimize the functionalization process of nickel oxide nanoparticles (NiO_x NPs) with 1-ethyl-3-methyl-imidazolium iodide (EMIMI) using ITO/NiO_x NPs/perovskite half-stack structures and correlating the transport phenomena with changes in surface chemistry and energetics. The spectroelectrochemical tool proves to be a valuable analytical methodology to study the quality and properties of buried interfaces in perovskite-based (opto)electronic devices, is agnostic with both hole- and electron-selective contacts, and conceivably extended to other semiconductor junctions, as it allows for quantification of surface effects and can predict device performance under operando conditions.