Exploring the Limiting Open‐Circuit Voltage and the Voltage Loss Mechanism in Planar CH₃NH₃PbBr₃ Perovskite Solar Cells

Perovskite solar cells based on CH 3 NH 3 PbBr 3 with a band gap of 2.3 eV are attracting intense research interests due to their high open‐circuit voltage ( V oc ) potential, which is specifically relevant for the use in tandem configuration or spectral splitting. Many efforts have been performed to optimize the V oc of CH 3 NH 3 PbBr 3 solar cells; however, the limiting V oc (namely, radiative V oc : V oc,rad ) and the corresponding Δ V oc (the difference between V oc,rad and V oc ) mechanism are still unknown. Here, the average V oc of 1.50 V with the maximum value of 1.53 V at room temperature is achieved for a CH 3 NH 3 PbBr 3 solar cell. External quantum efficiency measurements with electroluminescence spectroscopy determine the V oc,rad of CH 3 NH 3 PbBr 3 cells with 1.95 V and a Δ V oc of 0.45 V at 295 K. When the temperature declines from 295 to 200 K, the obtained V oc remains comparably stable in the vicinity of 1.5 V while the corresponding Δ V oc values show a more significant increase. Our findings suggest that the V oc of CH 3 NH 3 PbBr 3 cells is primarily limited by the interface losses induced by the charge extraction layer rather than by bulk dominated recombination losses. These findings are important for developing strategies how to further enhance the V oc of CH 3 NH 3 PbBr 3 ‐based solar cells.