Characterization of rf sputtered Sb2Te3 thin films for back contacts to CdS/CdTe solar cells

We have studied the morphology and transport properties of magnetron sputtered Sb2Te3 films including their suitability as back contacts for sputtered CdS/CdTe solar cells. Sb2Te3 films were sputtered onto boro-aluminosilicate glass at temperatures from ~30 °C (room temperature) to 270 °C and characterized by X-ray diffraction, Hall-effect studies, and thermoelectric power measurements. Some films received post-deposition annealing up to 350 °C. Over these conditions, grain size reached 80 nm, hole carrier concentration 2 × 1020 cm−3, mobility 170 cm2/V s, and Seebeck coefficient 260 µV/K. Two-micron-thick CdS/CdTe solar cells completed with Sb2Te3/Mo back contacts yielded 10 % efficiency; however the addition of 3 nm of Cu after the Sb2Te3 yielded >12 % efficiency. Comparative results are also given for 300 h of accelerated life testing under one-sun illumination at 85 °C.