Epitaxial growth of CIGSe layers on GaP/Si(001) pseudo-substrate for tandem CIGSe/Si solar cells

Abstract In this study, the epitaxial growth of co-evaporated Cu(In,Ga)Se2 films (CIGSe) onto GaP/Si(001) pseudo-substrates, where the GaP thin layer is epitaxially grown by Molecular Beam Epitaxy (MBE), is investigated. Extensive structural characterisation of epi-CIGSe is carried out via X-ray diffraction as well as transmission electron microscopy. Sturdy evidence of an epitaxial growth of CIGSe on (GaP/Si)(001) is observed, with the propagation of twins originating from the GaP/Si interface, through the CIGSe/GaP interface. This work aims at paving the way for future CIGSe/GaP/Si structures for the development of tandem solar cells with a c-Si bottom cell, and a GaP interfacial buffer layer for band edge engineering, allowing for the monolithic epitaxial growth of high quality CIGSe as a thin film top cell absorber.