Chemically Deposited SnSe Thin Films: Thermal Stability and Solar Cell Application

Compact and specularly reflective tin(II)selenide (SnSe) thin films 100–310 nm in thickness are deposited on Na2S-treated glass substrates from a chemical bath containing tin(II)chloride, triethanolamine, sodium hydroxide, and sodium selenosulfate. These thin films are of orthorhombic crystalline structure, which remains so even after heating them at 400°C. Partial conversion of SnSe to SnSe2 occurs only in films 100 nm in thickness when they are heated at 300 to 350°C, but the SnSe2 component tends to revert to SnSe in films heated at 400°C. The SnSe thin films have an optical bandgap of 0.95–1.14 eV. Their electrical conductivity is p-type, of 0.1–10 Ω−1 cm−1, with minor variation occurring with film thickness and heat-treatment. A CdS(100 nm)-SnSe(180 nm) solar cell using this film shows an open circuit voltage 215 mV, short circuit current density 1.7 mA/cm2, and conversion efficiency 0.1% under an illumination of 850 W/m2.