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 alpha-SnSe phase at selenium-rich side with pressures lower than atmospheric pressure and in the temperature range of 300-500 degrees 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 alpha-SnSe at 1.0 g of selenium. Further, alpha-SnSe/CdS interface was studied by photoelectron yield spectroscopy (PYS), which showed a 'type-I' band alignment with a valence-band offset (Delta E-v) of 1.3 eV and a conduction-band offset (Delta E-c) of 0.2 eV. Finally, alpha-SnSe solar cells with a device structure of soda-lime glass (SLG)/Mo/alpha-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.