Activation method of cadmium telluride thin films for creation effective solar cells

The influence of annealing in freon on the cadmium telluride films crystal structure obtained by closed space sublimation method and the output parameters and light diode characteristics of solar cells based on these films were studied. Annealing of structures was performed at a temperature of 400°С for different times. The studies of the crystal structure were performed by the X-ray diffraction analysis. These studies have shown that the annealing in freon leads to a recrystallization of cadmium telluride films, which reduces microstress. It is evidenced by the lattice period decrease after annealing from а = 6.491 Å to а = 6.488 Å. The study of the influence of annealing in freon on the output parameters and light diode characteristics of solar cells was performed. For this purpose the light current-voltage characteristics of ITO/SnO2/CdS/CdTe structures, annealed for 20‑40 minutes, were studied. It was found that the optimal annealing time in freon is 30 minutes. It is shown that the solar cells based on such films have the highest efficiency in 11.7% after annealing in freon for 30 minutes. A simulation of light diode characteristics influence on the efficiency showed that the solar cells efficiency increase due to the diode saturation current density decrease when the annealing time in freon increases to 30 minutes. When the annealing time increases to 40 minutes the efficiency decrease is associated with a shunt resistance decrease. It is also shown that the pre-irradiation of solar cells in the AM1.5 mode for 20 minutes leads to an additional efficiency increase to 12.2%. According to the simulation results, such efficiency increase is also due to the diode saturation current density decrease.