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

In this study, we prepared MoSe 2 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 MoSe 2 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 MoSe 2 , the photovoltaic performances of the devices decreased and that a thicker MoSe 2 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 ( E A ) 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 MoSe 2 thickness of about 80 nm, the device showed highest efficiency.