Towards Stable, 30% Efficient Perovskite Solar Cells

Solid-state perovskite solar cells (PSCs) were first discovered in 2012, where a power conversion efficiency (PCE) of 9.7% was demonstrated along with stability for 500 h at ambient atmosphere. Since then, the PCEs of PSCs have increased amazingly to over 26%. Moreover, perovskite/silicon tandem solar cells achieved a PCE as high as 34%. Such a superb photovoltaic performance is due to the inherent optoelectronic properties of halide perovskites. Here, the progress of PSCs is reported following a detailed description on the discovery of PSCs. The first solid-state PSCs were based on sensitization concept using a sub-micrometer mesoporous TiO₂ film whose surface was coated with nano-sized methylammonium lead iodide (MAPbI₃), which had evolved to n-i-p and p-i-n planar device structures. Recent high efficiencies were mostly demonstrated using formamidinium lead iodide (FAPbI₃) perovskite. To increase further the PCE to more than 30%, the current density should approach 28 mA/cm² and fill factor 90% while keeping the voltage near 1.2 V using a perovskite with bandgap less than ~ 1.47 eV (theoretical current density = 29.4 mA/cm²). Thus, a strategy should be well established to make a defect-minimized perovskite film and the interface-engineered PSCs as well. Finally, effective methodology for improving stability of PSCs is discussed.