Overcoming Redox Reactions at Perovskite-Nickel Oxide Interfaces to Boost Voltages in Perovskite Solar Cells

Nickel oxide (NiOx) hole transport layers (HTLs) are desirable contacts for perovskite photovoltaics because they are low cost, stable, and readily scalable; however, they deliver lower open-circuit voltages (V(OC)s) compared to organic HTLs. Here, we characterize and mitigate electron transfer-proton transfer reactions between NiOx HTLs and perovskite precursors. Using XPS and UPS characterization, we identify that Ni >= 3+ metal cation sites in NiOx thin films act both as Bronsted proton acceptors and Lewis electron acceptors, deprotonating cationic amines and oxidizing iodide species, forming PbI2-xBrx-rich hole extraction barriers at the perovskite-NiOx. interface. Titrating reactive Ni >= 3+ surface states with excess A-site cation salts during perovskite active layer deposition yielded an increase in V-OC values to 1.15 V and power conversion efficiencies of similar to 20%. This may be a general finding for metal oxide contacts that act as Bronsted and Lewis acid-base reactants toward perovskite precursors, an observation that has also been made recently for TiO2 and SnO2 contacts.

氧化镍（NiOx）空穴传输层（HTL）是钙钛矿光伏电池理想的接触层，因为它们成本低、稳定且易于规模化；然而，与有机空穴传输层相比，它们的开路电压（V(OC)）较低。在此，我们对氧化镍空穴传输层和钙钛矿前驱体之间的电子转移 - 质子转移反应进行了表征并加以缓解。通过XPS和UPS表征，我们发现氧化镍薄膜中Ni≥3+金属阳离子位点既作为布朗斯特质子受体，又作为路易斯电子受体，使阳离子胺去质子化并氧化碘化物，在钙钛矿 - 氧化镍界面形成富含PbI2 - xBrx的空穴提取势垒。在钙钛矿活性层沉积过程中，用过量的A位阳离子盐滴定具有反应性的Ni≥3+表面态，使V - OC值提高到1.15 V，功率转换效率接近20%。对于作为布朗斯特和路易斯酸碱反应物与钙钛矿前驱体发生反应的金属氧化物接触层，这可能是一个普遍的发现，最近在TiO2和SnO2接触层中也有类似观察结果。