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 (∆Ev) of 1.3 eV and a conduction-band offset (∆Ec) 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.