Thermal sulfurization effect on sprayed CZTS thin filmsproperties and CZTS/CdS solar cells performances

Cu2ZnSnS4 (CZTS) thin films were successfully deposited by a simple and inexpensive technique such as ultrasonic spray pyrolysis. The effect of sulfurization temperature on CZTS films properties and on Mo/CZTS/CdS/ZnO/ZnO:Al solar cell performances were studied. The investigated sulfurization temperatures were ranged from 450 °C to 550 °C. X-ray-diffraction pattern and Raman scattering spectroscopy confirmed the formation of monophase kesterite CZTS, the best crystallinity was obtained in the sample sulfurized at 450 °C. Atomic forces microscopy images indicated that annealing temperature increase yields to rough films with large grain size. UV–visible optical transmittance spectroscopy reveals that films enjoy a strong absorption with an absorption coefficient as high as 104 cm−3. Whereas, the optical band gap energy was found to decrease with sulfurization temperature. Hall effect measurements confirm the films p-type conductivity; the carriers concentration varies between 1014 and 1016 cm−3 when the sulfurization temperature changes from 450 °C to 550 °C. The I–V characteristics of the realized Mo/CZTS/CdS/ZnO/ZnO:Al cells indicated that all the devices show a rectification behavior with an ideality factor ranged from 1.6 to 1.8. The current transport is dominated by the interfacial recombination process. The photovoltaic effect was observed, the best performance was achieved in the device prepared with CZTS sulfurized film at 450 °C, the recorded characteristics are: 0.43% efficiency, 9.8 mA cm−2 short circuit current, 161 mV open circuit voltage and 28% fill factor. A comparison between the reported results obtained by different techniques reveals the superiority of the cells prepared with CZTS deposited by physical deposition technique such as thermal evaporation or sputtering.