Influence of the annealing temperature on CuAl _xGa _1-xSe ₂ thin films obtained by selenization

CuAl _xGa _1-xSe ₂ (CAGS) is an attractive wide-bandgap chalcopyrite for buffer and top cell in tandem solar cells avoiding the use of expensive In. Polycrystalline CAGS thin films with chalcopyrite structure and strongly oriented along the (112) plane have been obtained by a sequential process of vacuum evaporation and selenization, with different x values ranging from 0 to 1. The temperature of selenization has been varied between 450 and 550 °C and it has resulted on a critical parameter in the complete and homogeneous formation and crystalline quality of the CAGS thin films. The proportion of Al(x) also affects the temperature required for selenization. At least 500 °C is necessary to obtain complete formation of CAGS for x > 0.1 whereas for x ≤0.1 the formation takes place in a wide range of annealing temperatures. Resistivity, roughness, band gap energy, texture coefficient bsubesub and crystallite size tend to increase as the selenization or annealing temperature increases. CAGS thin film properties are optimized at 525acirc° for high Al proportions for which some deterioration proceeded at higher temperatures whereas at low Al proportions, a similar behaviour for 525 and 550a;circ° is observed. ©