Influence of an interfacial cesium oxide thin layer in the performance and internal dynamic processes of GaSe9 solar cells

Solar cells based on evaporated Cs2O/GaSe9 and Cs2O/Se (as comparison) active layers have been investigated. We correlate their performance with devices previously reported without Cs2O. GaSe9 appears as a very promising solar absorber because of its attractive optical and electrical properties. We improved device performance by around 30% by inserting a Cs2O thin interlayer. Current density-voltage, capacitance-voltage and impedance spectroscopy measurements were used to characterize the effect of Cs2O layer on device performance. The charge carrier concentration and the built-in potential were derived using Schottky-Mott relation. The enhancement promoted by Cs2O is attributed to an improvement in electron extraction efficiency by FTO, and the avoidance of Se sublimation during the annealing process. The insertion of the metallic oxide also increases the built-in potential at FTO/GaSe9 interface. Dynamic processes were clearly identified by impedance spectroscopy under complex modulus analysis, confirming better capabilities of charge collection by the Cs2O containing electrodes.