Overcoming the Photovoltage Plateau in Large Bandgap Perovskite Photovoltaics

Development of large bandgap (1.80-1.85 eV E_g) perovskite is crucial for perovskite-perovskite tandem solar cells. However, the performance of 1.80-1.85 eV E_g perovskite solar cells (PVKSCs) are significantly lagging their counterparts in the 1.60-1.75 eV E_g range. This is because the photovoltage (V_oc) does not proportionally increase with E_g due to lower optoelectronic quality of conventional (MA,FA,Cs)Pb(I,Br)₃ and results in a photovoltage plateau (V_oc limited to 80% of the theoretical limit for ∼1.8 eV E_g). Here, we incorporate phenylethylammonium (PEA) in a mixed-halide perovskite composition to solve the inherent material-level challenges in 1.80-1.85 eV E_g perovskites. The amount of PEA incorporation governs the topography and optoelectronic properties of resultant films. Detailed structural and spectroscopic characterization reveal the characteristic trends in crystalline size, orientation, and charge carrier recombination dynamics and rationalize the origin of improved material quality with higher luminescence. With careful interface optimization, the improved material characteristics were translated to devices and V_oc values of 1.30-1.35 V were achieved, which correspond to 85-87% of the theoretical limit. Using an optimal amount of PEA incorporation to balance the increase in V_oc and the decrease in charge collection, a highest power conversion efficiency of 12.2% was realized. Our results clearly overcome the photovoltage plateau in the 1.80-1.85 eV E_g range and represent the highest V_oc achieved for mixed-halide PVKSCs. This study provides widely translatable insights, an important breakthrough, and a promising platform for next-generation perovskite tandems.