CdTe grown under Cd/Te excess at very low temperatures for solar cells

Abstract

A low-temperature physical vapour deposition method for CdTe absorber layers was developed in this study and the influence of the substrate temperature during absorber growth is discussed in terms of the phase diagram of CdTe. The composition of CdTe layers grown at substrate temperatures between 45 and 300 °C with 3 different evaporation source arrangements producing either a stoichiometric, a Te-rich or a Cd-rich material supply was investigated by energy-dispersive X-ray spectroscopy. Absorber layers which were produced below a substrate temperature of 190 °C with the standard evaporation method using stoichiometric CdTe as source material show a significant Te excess which leads to non working solar cells. The application of Cd-rich material supply yields a stoichiometric growth of the absorber layers and good solar cell characteristics for substrate temperatures as low as 100 °C.