Comparison of different conducting oxides as substrates for CdS/CdTe thin film solar cells

Abstract

A study of several types of transparent conducting oxides (TCO) is reported. In particular we have investigated the interaction between the TCO and CdS layers from the point of view of the completed CdS/CdTe solar cell parameters in respect to the deposition parameters of the TCO films. All different TCO films are deposited by sputtering in pure argon or in argon +hydrogen, Ar+CHF 3, argon+Oxygen. The kinds of TCO studied are: tin doped In 2O 3, fluorine doped In 2O 3, Cd 2SnO 4, germanium doped In 2O 3 (IGO), SnO 2, and Zn 2SnO 4. The devices are fabricated with a single TCO layer, i.e. fluorine doped In 2O 3, or in a double layer configuration, i.e. IGO covered by SnO 2. We have found that the performance of the device depends strongly on the interaction between the surface of the TCO and the CdS film. This interaction derives overall from the stability of the Oxygen atoms on the surface of the TCO films. This fact is clarified observing the behavior of the cells performance: the device is better if the TCO layer in contact with the CdS film is deposited in Ar+H 2 atmosphere. The best CdS/CdTe solar cells, with an efficiency of approximately 14%, are obtained by using 0.4 μm of fluorine doped In 2O 3 as a TCO. The sputtering atmosphere used for the deposition of this kind of TCO is a mixture of Ar, Ar+H 2 and CHF 3.