Inorganic p-type materials show great potential as the hole transport layer in perovskite solar cells with the merits of low costs and enhanced chemical stability. As a p-type material, cobalt oxide (CoO) has received so far not that level of attention despite its high hole mobility. Herein, solution-processed p-type CoO nanocrystalline films are developed for inverted mixed perovskite solar cells. The ultrafine CoO nanocrystals are synthesized via an oil phase method, which are subsequently treated by a ligand exchange process using pyridine solvent to remove the long alkyl chains covering the nanocrystals. From this homogeneous colloidal solution CoO films are obtained, which exhibit a smooth and pin-hole free surface morphology with high transparency and good conductivity. The ultraviolet photoelectron spectrum also indicates that the energy levels of the CoO film match well with the mixed perovskite Cs0.05(FA0.83MA0.17)0.95(I0.83Br0.17)3. Inverted solar cells based on crystalline CoO films with ligand exchange show a reasonable energy conversion efficiency, whereas devices based on CoO films without ligand exchange suffer from a strong S-shape JV-characteristic. Thus, the crystalline CoO films are foreseen to pave a new way of inorganic hole transport materials in the fields of perovskite solar cells.

中文翻译：

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用于倒置混合钙钛矿太阳能电池的溶液处理的p型纳米晶体CoO膜。

无机p型材料在钙钛矿型太阳能电池中具有作为空穴传输层的巨大潜力，具有成本低廉和化学稳定性增强的优点。作为p型材料，氧化钴（CoO）尽管具有很高的空穴迁移率，但迄今为止还没有引起人们的关注。在本文中，溶液处理的p型CoO纳米晶体膜被开发用于倒置的混合钙钛矿太阳能电池。通过油相法合成超细CoO纳米晶体，然后使用吡啶溶剂通过配体交换工艺对其进行处理，以去除覆盖纳米晶体的长烷基链。从该均匀的胶体溶液中获得了CoO膜，其具有光滑且无针孔的表面形态，具有高透明度和良好的导电性。紫外光电子光谱还表明，CoO薄膜的能级与混合钙钛矿Cs0.05（FA0.83MA0.17）0.95（I0.83Br0.17）3匹配良好。基于具有配体交换的结晶CoO薄膜的倒置太阳能电池显示出合理的能量转换效率，而基于基于CoO薄膜而无配体交换的器件则具有很强的S形JV特性。因此，可以预见晶体CoO膜将为钙钛矿太阳能电池领域中的无机空穴传输材料铺平道路。而基于CoO薄膜且不进行配体交换的器件具有很强的S形JV特性。因此，可以预见晶体CoO膜将为钙钛矿太阳能电池领域中的无机空穴传输材料铺平道路。而基于CoO薄膜且不进行配体交换的器件具有很强的S形JV特性。因此，可以预见晶体CoO膜将为钙钛矿太阳能电池领域中的无机空穴传输材料铺平道路。