α-SnSe thin film solar cells produced by selenization of magnetron sputtered tin precursors

The temperature-pressure-composition phase diagrams of Sn-Se system were calculated using the CALPHAD (CALculation of PHase Diagram) models. The phase diagrams showed the formation of α-SnSe phase at selenium-rich side with pressures lower than atmospheric pressure and in the temperature range of 300–500 °C. As a first step, the effect of Sn/Se ratio on the phase formation was studied experimentally by selenization of tin metal precursor films using effusion cell evaporation. The Sn/Se ratio was varied by changing the selenium weight in the range of 0.5–1.5 g. The physical properties of the films were studied with suitable characterization techniques and the obtained results showed the formation of single phase α-SnSe at 1.0 g of selenium. Further, α-SnSe/CdS interface was studied by photoelectron yield spectroscopy (PYS), which showed a ‘type-I’ band alignment with a valence-band offset (∆E_v) of 1.3 eV and a conduction-band offset (∆E_c) of 0.2 eV. Finally, α-SnSe solar cells with a device structure of soda-lime glass (SLG)/Mo/α-SnSe/CdS/i-ZnO/Al:ZnO/Ni/Ag were fabricated and a power conversation efficiency of 1.42% was achieved at 1.0 g of selenium.