Comparing the Calculated Fermi Level Splitting with the Open-Circuit Voltage in Various Perovskite Cells

While the power conversion efficiency of metal halide perovskite (MHP) solar cells has increased enormously, the open-circuit voltage, Voc, is still below the conceivable limit. Here, we derive the Fermi level splitting, μF, for various types of noncontacted MHPs, which sets a limit for their achievable Voc, using rate constants and mobilities obtained from time-resolved photoconductivity measurements. Interestingly, we find that for vacuum-evaporated MAPbI3 and K+-doped (MA,FA,Cs)Pb(I/Br)3, the μF/e values are close to the reported Voc values. This implies that for an improvement of the Voc, charge carrier recombination within the bare perovskite has to be reduced. On the other hand, for MHPs with Cs+ and/or Rb+ addition, the experimental Voc is still below μF/e, suggesting that higher voltages are feasible by optimizing the transport layers. The presented approach will help to select which techniques and transport layers are beneficial to improve the efficiency of MHP solar cells.