Polyoxometalate Reinforced Perovskite Phase for High-Performance Perovskite Photovoltaics.

Ionic hybrid perovskites face challenges in maintaining their structural stability against non-equilibrium phase degradation, therefore, it is essential to develop effective ways to reinforce their corner-shared [PbI] octahedral units. To strengthen structural stability, redox-active functional polyoxometalates (POMs) are developed and incorporated into perovskite solar cells (PSCs) to form a robust polyoxometalates/perovskite interlayer for stabilizing the perovskite phase. This approach offers several advantages: 1) promotes the formation of an interfacial connecting layer to passivate interfacial defects in addition to stabilize the [PbI] units through exchanged ammonium cations in POMs with perovskites; 2) facilitates continuous structural repairing of Pb- and I-rich defects in the [PbI] unit through redox electron shuttling of the electroactive metal ions in POMs; 3) provides guidance for selecting suitable redox mediators based on the kinetic studies of POM's effectiveness in reacting with targeted defects. The POM-reinforced device maintains 97.2% of its initial PCE after 1500 h of shelf-life test at 65 °C, while also enhancing the long-term operational stability. Additionally, this approach can be generally applicable across scalable sizes and various bandgap perovskites in devices, showing the promise of using functional POMs to enhance perovskite photovoltaic performance.