Ecofriendly Mn₃O₄ as a Novel Hole Transport Material for Efficient and Ultrastable Flexible and Rigid Perovskite Solar Cells

Exploring ecofriendly, low-cost, and chemically stable hole transport materials (HTMs) is of great significance for the commercial application of perovskite solar cells (PSCs). In view of this, we first employed the inorganic p-type semiconductor trimanganese tetraoxide (Mn3O4) as a HTM prepared by vacuum vapor deposition for flexible and rigid PSCs. It was revealed that the Mn3O4 material presented a suitable band structure, outstanding electrical conductivity, and hole mobility, which was a potential HTM for PSCs. The optimized flexible and rigid PSCs based on the Mn3O4 thickness (50 nm) achieved the best photoelectric conversion efficiencies (PCEs) of 15.58 and 18.07%, respectively. More importantly, the unencapsulated rigid device based on Mn3O4 exhibited outstanding stability and retained 91.7% of the original PCE after storage for 1000 h at double 85 condition (85 degrees C and 85 +/- 5% relative humidity). Additionally, the target flexible PSCs still maintained 92.3% of the initial efficiency after 1000 bending cycles with a radius of 5 mm. Obviously, the Mn3O4 semiconductor is a promising candidate as a HTM compatible with flexible and rigid PSCs, which plays a pivotal role in improving the stability of the devices. It is believed that our research results provide new insights for realizing cost-effective and ultrastable photovoltaic devices.