CuGaO₂ Nanosheets and CuCrO₂ Nanoparticles Mixed with Spiro-OMeTAD as the Hole-Transport Layer in Perovskite Solar Cells

Organic small molecules such as 2,2′,7,7-tetrakis (N, N′-di-p-methoxyphenylamine)-9,9’-Spiro-OMeTAD-bifuorene (Spiro-OMeTAD) have been widely used as the hole-transport layer (HTL) for perovskite solar cells (PSCs). However, the long-term stability of devices using Spiro-OMeTAD is low despite the high photoelectric conversion efficiency (PCE). In this work, low-cost p-type CuGaO2 (CGO) nanosheets and CuCrO2 (CCO) nanoparticles were synthesized using a hydrothermal method, which was mixed with Spiro-OMeTAD to prepare uniform and well-covered HTLs. Correspondingly, a hierarchical energy arrangement was constructed between the perovskite layer and the Ag electrode. Hence, blended HTLs with lower interface trap density obtained better hole carrier extraction and transport performance, which inhibited charge recombination and thus improved the photoelectric performance of the devices. The experimental results show that the improvement of current density (JSC), especially the open-circuit voltage (VOC) and the filling factor (FF), for optimal devices based on blended HTLs, achieved a stable PCE of 19.50%. More importantly, the unsealed CCO/Spiro-OMeTAD devices maintained over 90% of the initial efficiency after 800 h of storage under 20 °C and an ambient humidity of 50–80%. Therefore, resistance to water erosion in the air could significantly improve the long-term stability of PSCs.