Thermally evaporated AgGaTe2 thin films for low-cost p-AgGaTe2/n-Si heterojunction solar cells

High quality polycrystalline AgGaTe2 (AGT) thin films were deposited on H-terminated n-Si substrates by controlled thermal evaporation method at various substrate temperatures (300-500 K). X-ray diffraction (XRD) studies showed that all films were of chalcopyrite structure and while the films were deposited at 300 K had random grain orientation, the films deposited at higher substrate temperature (500 K) showed preferred (112) orientation. The composition of the films was thoroughly analyzed by energy dispersive x-ray analysis (EDAX) and by x-ray photoelectron spectroscopy (XPS) with and without argon ion etching. The ultraviolet-visible (UV-Vis) spectra showed the optical bandgap of 1.16 eV, with sharper band edge for the films deposited at higher temperature. The films were p-type and the resistivities of the as deposited at 300 and 500 K were 2.8 x 10(4) and 1.2 x 10(3) Omega. cm respectively. p-AgGaTe2/n-Si heterojunction solar cells, having an active area of 0.12 cm(2) and without any antireflection coating, were fabricated. It was observed that the films deposited at 500 K produced junctions with improved photovoltaic properties. Under solar simulator AM1 illumination, the improved junctions exhibited an efficiency of 4.8% whereas the films deposited at 300 K showed an efficiency of 2.1%.