Stoichiometry control of CdTe thin film solar cells by close-spaced sublimation

The control of the native defects in the CdTe thin film solar cells was investigated by using a novel source for a close-spaced sublimation (CSS) process which was prepared by vacuum evaporation with elemental Cd and Te (evaporated source). The evaporated sources were prepared on glass substrates at room temperature, and Cd/Te ratio was controlled by varying the Cd and Te beam equivalent pressures. In the cells using the Te-rich source, the conversion efficiency was less than 0.2 % because of the extremely low shunt resistance. On the other hand, the conversion efficiency above 15 % was obtained by using the Cd-rich source. C-V characteristics revealed that the acceptor concentration in the CdTe layer increased with increasing the Cd/Te ratio of the evaporated source. Furthermore, photoluminescence spectra implied that the formation of the Cd vacancies in the CdTe layer was suppressed by using the Cd-rich source