Formation and characterisation of MoSe2 for Cu(In,Ga)Se2 based solar cells

Abstract The reaction kinetics of the MoSe2 formation have been investigated by selenizing Mo layers in Se vapor at different temperatures and for different durations. The samples were characterized by means of Rutherford backscattering spectrometry, X-ray diffraction (XRD), electron diffraction, and by bright-field and high-resolution transmission electron microscopy. It was found that in all samples, a homogeneous MoSe2 layer is formed on top of the Mo layer. The temperature dependence shows that the MoSe2 layer thickness increases strongly for temperatures higher than ca. 550 °C. At a substrate temperature of 450 °C, no difference in the MoSe2 thickness was detected for samples selenized for different durations. The diffusion constant of Se in MoSe2 is estimated from the selenization duration dependence of MoSe2 layer thicknesses at 580 °C. Finally, Cu(In,Ga)Se2 (CIGS) solar cells in substrate configuration were developed on indium tin oxide (ITO) transparent back contacts. An intentionally grown MoSe2 intermediate layer on ITO, prior to CIGS deposition, causes a significant efficiency improvement, suggesting that MoSe2 can facilitate a quasi-ohmic contact. Solar cell efficiencies of up to 11.8% are obtained using an ITO/MoSe2 back contact.