Optimization of the Electron Transport Layer Thickness in Perovskite Solar Cells

In perovskite solar cells (PSCs), the electron transport layer (ETL) plays a fundamental role in the cell’s performance by selectively extracting electrons from the absorber and rejecting holes. Deposition of a uniform ETL with a well-tuned thickness is essential to reaching high power conversion efficiencies (PCEs). In this work, layers of Fullerene-C₆₀ (C60) and bathocuproine (BCP) are deposited via physical vapor deposition (PVD) on top of the absorber layer of a FAPbI₃ PSC to form the ETL. Thicknesses of C60 and BCP are systematically varied, and completed devices are tested by current-voltage sweeps at simulated 1-sun illumination. We present results from a thorough search of the layer thickness space, with the main figure of merit being PCE, with supporting characterization provided by implied JV analysis and JV curve fitting. Of the tested conditions, the highest PCE values were 15.45% with 13 nm BCP on 31 nm C60 and 14.08% with 13 nm BCP on 36 nm C60. From these results, we conclude that the optimal thicknesses for C60 and BCP are 36 nm and 13 nm respectively when applied to our baseline device stack. In the future, we plan to test the addition of inert, tunnel junction layers such as LiF or MgF₂ to decrease non-radiative recombination at the ETL/perovskite junction.