Insights into Recombination Processes from Light Intensity-Dependent Open-Circuit Voltages and Ideality Factors in Planar Perovskite Solar Cells

To analyze the dominant recombination, researchers often consider the diode ideality factor (n(id)), determined from the fitting of a semi-log plot of light intensity-dependent open-circuit voltage (V-oc(lnI/I-0)) to a linear dependence. This value is called n(id,Voc). Theoretically, n(id) is the exponential dependence factor in the recombination rate function of the split of quasi-Fermi levels. This n(id) is called n(id,C). Herein, correlations between n(id,Voc), n(id,C), and the dominant recombination are reconsidered using a validated numerical drift-diffusion model and a diode current analysis in perovskite solar cell devices having accumulations of charged defects near the carrier transporting interfaces. It is found that the interplay between the recombination processes affects the linearity of the V-oc(lnI/I-0) plots. Devices having a single dominant recombination process exhibit V-oc(lnI/I-0) plots that appear to be linear, resulting in n(id,Voc) approximate to n(id,C) of the dominant recombination. Conversely, bends in the V-oc(lnI/I-0) curves indicate that different (multiple) recombination mechanisms dominate at different light intensities, so n(id,Voc) is an effective n(id) of the total diode current whose value is not consistent with any n(id,C) values. This work provides more understanding of n(id) and how to interpret a V-oc(lnI/I-0) curve more correctly for the insights into recombination mechanisms.