Bi2Te3 thin films prepared by co-evaporation for CdTe thin film solar cells

•Bi2Te3 was prepared by thermal co-evaporation.•Bi2Te3 was used as a buffer layer to form an ohmic back contact to CdTe solar cells.•Bi2Te3 was used as a Bi-doping source to enhance collection of photogenerated carriers.

Bi2Te3 thin films were fabricated by vacuum co-evaporation and the properties of the films were investigated using X-ray diffraction, Hall measurements, and synchrotron radiation photoemission spectroscopy. The results indicate that p-type Bi2Te3 films, which have a work function of about 5.4 eV and carrier concentration of the order of 1021 cm−3, are a rhombohedral phase with a strong (105) preferred orientation. A co-evaporated Bi2Te3 buffer layer was used for a back contact to CdTe thin film solar cells. C–V measurements, light and dark J–V measurements, and spectral response analysis also show that the p back contact has greatly enhanced cell performance.