Enhanced efficiency in perovskite solar cells by eliminating the electron contact barrier between the metal electrode and electron transport layer

Abstract

Interface modifying layers (IMLs) play a pivotal role in the improved performance of perovskite solar cells (PSCs). Herein, we report a new IML based on Bphen:Cs₂CO₃:BCP (BCB), which is inserted at the interface of phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) and a Ag electrode. Consequently, the efficiency of PSCs is significantly improved by 5% (from 17.57% to 18.29%), mainly due to the increased open circuit voltage (V_OC). It is revealed by ultraviolet photoelectron spectroscopy (UPS) that the work function of Ag is reduced from 4.68 eV to 3.90 eV, after being modified by BCB due to the formation of a strong negative interfacial dipole at the Ag/BCB interface. The decreased work function of Ag improves the ohmic contact between PC₆₁BM and Ag, facilitating carrier extraction and suppressing the charge recombination at the interface of PC₆₁BM and the Ag electrode. As a result, the reverse saturation current of the final PSC is decreased by approximately one order of magnitude, which is consistent with a larger V_OC. Our work provides a comprehensive understanding of the interface between a metal electrode and an electron transporting layer (ETL), and hence paves a way towards better interfacial engineering and highly efficient solar cells.