Modeling of light interference in CH3NH3PbI3Clx and MAPbI3Cl perovskite solar cells

• Degradation/recovery of perovskite solar cells is mostly dependent on variation of Fill Factor.
• Both slow and fast metastable defects are responsible in fill factor degradation/recovery.
• Three different models for degradation/recovery of efficiency, Jsc, and FF are in agreement.

For the first time, we modeled the optical losses in organic-inorganic CH3NH3PbI3−xPbI3−xClx and MAPbI3−xMAPbI3−xClx Perovskite solar cells taking into account the interference and multiple reflection effects. This model is rather simple than the conventionally used Optical Matrix for calculating the reflection and absorption rates in heterojunction devices. The input parameters are only the refractive index and extinction coefficient of every layer in device structure and the outputs are the short-circuit current density and efficiency as well as their loss percentage at the junctions. In contrast to the simulation results presented in the literature, this model does not ignore the multiple reflections and interference effects in perovskite layers. Therefore, slightly different results are presented which are different than the literature report but are closer to the experimentally established data. This claim is proven by comparing the transmission and reflection rates calculated with normal reflections and interference. The periodic changes (oscillations) in the simulation results are an evidence of the interference effects which has been neglected in the literature models. This suggests that the interference effect occurs in perovskite layers similar to anti-reflection coating and it is not negligible for thick layers.