Hye Ri Jung1,Hanseul Lee1,Namhee Kwon1,Soohyung Park1,Gee Yeong Kim1
Korea Institute of Science and Technology1
Hye Ri Jung1,Hanseul Lee1,Namhee Kwon1,Soohyung Park1,Gee Yeong Kim1
Korea Institute of Science and Technology1
Nickel oxide (NiO<sub>x</sub>) has been widely used as a hole transport layer in inverted perovskites solar cells owing to its high-mobility, low cost, and superior stability. Unfortunately, NiO<sub>x</sub> tends to form unpleasant reactants in contact with perovskite depending on the valency of nickel ion. Reactants formed by de-protonizing with cationic ammonium and oxidizing iodide species act as hole extraction barriers in the NiO<sub>x</sub>-perovskite interface [1]. These reactants lower the V<sub>OC</sub> and promote device degradation, especially when operating the device. In previous studies, various insertion layers have been proposed to alleviate the interfacial reaction at the NiOx-perovskite. However, the origin of the reaction process depending on the surface state of NiO<sub>x</sub> and its effect on perovskite solar cell’s stability has not been fully understood. Therefore, in this study, we fabricated perovskite solar cells and investigated the reaction process and decomposition mechanism with different surface states of NiO<sub>x</sub> (one is for nanoparticle NiO layer the other one is for sputtered NiO<sub>x</sub> thin-film). The origin of this reactant is identified through <i>in-operando</i> XPS, TEM and electrical measurements. From <i>in-operando</i> XPS, we observed compositional changes and carrier transport in NiO<sub>x</sub>-perovskite by applying an external voltage to elucidate charge transfer and decomposition mechanisms in real-time device operation. The result shows that two different types of NiO<sub>x</sub> displayed a significant difference in the Ni<sup>3+</sup>/Ni<sup>2+</sup> ratio, which in turn affects the stability of the device. The decomposition is induced by the reactants in NiO<sub>x</sub>-perovskite and the insertion layer retards the decomposition of perovskite solar cell. We also measured the formation of reactants and the morphology variation of the NiO<sub>x</sub>-perovskite interface through TEM over time. As a result, our experiment suggests that the proper insertion layer can control interface degradation and improve hole extraction, thereby efficiently promoting charge separation and suppressing recombination. These results provide insight into the origin of degradation at the NiO<sub>x</sub>-Perovskite interface.<br/><br/><b>References</b><br/>[1] C. C. Boyd, <i>et al.</i> Overcoming Redox Reactions at Perovskite-Nickel Oxide Interfaces to Boost Voltages in Perovskite Solar Cells.<i> Joule</i> <b>2020</b>, 4, 1759–1775. https://doi.org/10.1016/j.joule.2020.06.004