MAPbCl₃ Light Absorber for Highest Voltage Perovskite Solar Cells

Perovskite solar cells (PSCs) excel in achieving high open-circuit voltages (V (OC)) for narrow bandgaps (similar to 1.6 eV) but face challenges with wide-bandgap perovskites, like methylammonium lead trichloride (MAPbCl(3)) with a 3.03 eV bandgap. These materials are transparent in visible absorbing ultraviolet (UV) light. However, achieving uniform film crystallization remains a hurdle. Here, we enhance MAPbCl(3) crystallization by manipulating annealing atmospheres (nitrogen, air, and MACl vapor). Excess MACl vapor improves surface coverage, which is crucial for film stability. We demonstrate that the microstructure of the perovskite film, including surface morphology, grain boundaries, and interfaces, can affect the photovoltaic properties. The subsequently obtained V (OC) of 1.78 V is the highest recorded for single-junction PSCs to the best of our knowledge. Surprisingly, the conventional hole-transport layer spiro-OMeTAD, optimized for narrow bandgaps, sustains such high voltages. Photoluminescence measurements reveal a trap-assisted recombination peak at 1.65 eV, indicating deep traps as significant to voltage loss in MAPbCl(3).