Formation and characterization of MoSe2 interfacial layer in flexible CIGS thin film solar cells

In this study, we prepared MoSe2 layers and varied their thicknesses to observe the formation behavior at different selenization temperatures and the impact on the I–V characteristics of copper indium gallium selenide thin film solar cells. Field emission scanning electron microscopy was used to measure the cross-sectional thickness of the MoSe2 film, and X-ray diffraction to identify its structure. In addition, the temperature-dependent open-circuit voltage (Voc) was measured at temperatures from 80 to 300 K to analyze the recombination at the back contact. We found that with increasing the thickness of MoSe2, the photovoltaic performances of the devices decreased and that a thicker MoSe2 meant a higher electrical resistivity of the devices. In addition, the external quantum efficiency show a reduction in carrier collection, short-circuit current, at wavelengths beyond 700 nm, which implies a high recombination at the back contact. Furthermore, the measurement of the temperature-dependent Voc showed that the activation energy (EA) of the best cell was less than the bandgap of the device, which corresponds to drop in the value of the Voc and the fill factor. Our study showed that at a MoSe2 thickness of about 80 nm, the device showed highest efficiency.