Influence of Urbach Energy, Temperature, and Longitudinal Position in the Active Layer on Carrier Diffusion Length in Perovskite Solar Cells

Abstract

The diffusion length of charge carriers in the active layer of a perovskite solar cell (PSC) of the structure Glass/PEDOT: PSS/CH₃ NH₃ PbI₃ /PC60BM/Al is modelled. It is found that the diffusion length depends on the position x in the active layer measured from the PEDOT: PSS interface, Urbach energy and temperature. By varying the voltage in the range from zero to $V_{oc}$ , it is shown that the dependence of diffusion length on the position x in the active layer reduces at higher voltage. The combined influence of applied voltage and temperature on the diffusion length of charge carriers is investigated and it is found that in the low voltage range the diffusion length is temperature independent, but it becomes significantly temperature dependent at higher voltages. Also, it is found that the diffusion length decreases as the applied voltage increases and this reduction becomes much more significant at higher voltage and temperatures. The combined influence of applied voltage and Urbach energy on diffusion length of charge carriers reveals that the diffusion length decreases when both the applied voltage and Urbach energy increase. However, the reduction in the diffusion length due to the increase in Urbach energy becomes less significant at higher voltage.

Keywords: Urbach energy; active layer; applied voltage; diffusion length; perovskite solar cells.