Resumen de Cu(In,Ga)Se_2 thin films processed by co-evaporation and their application into solar cells
J. Sastre-Hernández, M.E. Calixto, M. Tufiño-Velázquez, G. Contreras-Puente, A. Morales-Acevedo, G. Casados-Cruz, M. A. Hernández-Pérez, M.L. Albor-Aguilera, R. Mendoza-Pérez
Polycristalline Cu(In,Ga)Se_2 (CIGS) solar cells are attractive because low cost techniques can be used to obtain high efficiency thin film photovoltaic devices. Several research groups around the workd have developed CIGS/CdS solar cells with efficiencies larger than 15% [1] using evaporation, making it an attractive and reliable technique for thin film deposition. Our PVD system is provided with MBE-type Knudsen cells to deposit CIGS thin films on glass/Molibdenum (Mo) substrates. The deposition conditions for each metal source have been established by doing a deposition profile of temperature data vs. growth rate by co-evaporation to obtain CIGS thin film for solar cells. Characterization of the co-evaporated CIGS thin films was performed by X-ray diffraction (X-RD), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) techniques. Good quality polycrystalline films were obtained as shown by X-RD patterns. SEM micrographs show films having a very uniform appearance with large grain sized (aprox 1 (micro)m). Photoluminescence (PL) studies on CIGS samples with different Ga and Cu concentrations (Ga/Ga+In) = 0.25 and 0.34 and (Cu/In+Ga) = 0.83, 0.88 and 0.94) have been performed. The EDS results have shown that is prossible to control very precisely the CIGS thin film composition using these Knudsen cells. Film thicknesses of (aprox) 3-4 (micro)m, were measured with an Ambios profilemeter XP 100 stylus type. A conversion efficiency of 10.9% has been achieved for solar cells made from the co-evaporated absorbers.
