Ledinský, M., Vlk, A., Schönfeldová, T., Holovský, J., Aydin, E., Dang, H. X., ... & De Wolf, S. (2020). Impact of Cation Multiplicity on Halide Perovskite Defect Densities and Solar Cell Voltages. The Journal of Physical Chemistry C.
This study, which took place in JPCC, demonstrates the correlation between the Urbach energy of perovskite absorbers and open-circuit voltage deficiency at the solar cell level.
Metal-halide perovskites feature very low deep-defect densities, thereby enabling high operating voltages at the solar cell level. Here, by precise extraction of their absorption spectra, we find that the low deep-defect density is unaffected when cations such as Cs+ and Rb+ are added during the perovskite synthesis. By comparing single crystals and polycrystalline thin films of methylammonium lead iodide/bromide, we find these defects to be predominantly localized at surfaces and grain boundaries. Furthermore, generally, for the most important photovoltaic materials, we demonstrate a strong correlation between their Urbach energy and open-circuit voltage deficiency at the solar cell level. Through external quantum yield photoluminescence efficiency measurements, we explain these results as a consequence of nonradiative open-circuit voltage losses in the solar cell. Finally, we define practical power conversion efficiency limits of solar cells by taking into account the Urbach energy.