Conventional inorganic p-type conductive oxides, for example, NiO, CuO X , and CuCrO X , can serve as low-cost and efficient hole transport materials for wide-bandgap organolead halide perovskites [for example, MAPbI 3 ] but fail for low-bandgap Snrich organometallic perovskites, for example, (FASnI 3 ) 0.6 (MAPbI 3 ) 0.4 , where MA = (CH 3 NH 3 ) and FA = (HC(NH 2 ) 2 ). In this work, we explore spinel Co 3 O 4 -based p-type conductive oxides as hole transport materials in organometallic halide MAPbI 3 and (FASnI 3 ) 0.6 (MAPbI 3 ) 0.4 perovskite solar cells. We examine the structural, crystalline, optical, electrical, photo-electrochemical, and surface chemistry properties of spin-coated Co 3 O 4 films without and with lithium doping. We find that lithium doping improves hole mobilities and film optical transparency and causes a lithium-enriched overlayer (e.g., LiCoO 2 ) forming at the Co 3 O 4 film surface. As a result, lithium doping can maximize the hole transport properties of Co 3 O 4 in our inverted planar perovskite solar cells, achieving about 14 and 7% light-to-electricity power conversion efficiencies (PCEs) for perovskite halides MAPbI 3 and (FASnI 3 ) 0.6 (MAPbI 3 ) 0.4 , respectively. This work underscores that cobaltite spinels hold promise for application as working HTLs for all kinds of organometallic halide perovskites.

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The defect-copper chalcopyrite CuGa3Se5 is a promising photocathode material for solar hydrogen generation. Here we assess its performance with photoelectrochemical measurements and vibrating Kelvin probe surface photovoltage spectroscopy.

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