Effect of the Electron Transport Layer Thickness on I–V Characteristics of the S-Shaped Kinks in Perovskite Solar Cells

In our experimental preparation of perovskite solar cells (PSCs), when the thickness of the electron transport layer (ETL) was changed from thin to thick, the current–voltage ( ${I}$ – ${V}$ ) characteristics showed the changing laws of S-shaped kinks appearance, S-shaped kinks disappearance, and S-shaped kinks appearance. A lumped-parameter equivalent circuit model is proposed to reveal the intrinsic physical significances of the S-shaped kinks for this variation laws. The explicit solution of the model is derived using the deformed difference-microvariation (DM) principle combined with the region method, and the model parameters are extracted efficiently through the firefly optimization algorithm (FA). The proposed analytical solution enables the model to be compactly implemented in photovoltaic devices and circuit simulators, and the model is expected to point the direction for process optimization of devices.