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

Perovskite solar cells based on CH₃NH₃PbBr₃ 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 CH₃NH₃PbBr₃ solar cells; however, the limiting V_oc (namely, radiative V_oc:V_oc,rad) and the corresponding ΔV_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 CH₃NH₃PbBr₃ solar cell. External quantum efficiency measurements with electroluminescence spectroscopy determine the V_oc,rad of CH₃NH₃PbBr₃ cells with 1.95 V and a ΔV_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 ΔV_oc values show a more significant increase. Our findings suggest that the V_oc of CH₃NH₃PbBr₃ 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 CH₃NH₃PbBr₃‐based solar cells.