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

A study of several types of transparent conducting oxides (TCO) is reported. In particular we have investigated the interaction between the TCO and US 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 + CHF3, argon + Oxygen. The kinds of TCO studied are: tin doped M2O3, fluorine doped In2O3, Cd2SnO4, germanium doped In2O3 (IGO), SnO2, and Zn2SnO4. The devices are fabricated with a single TCO layer, i.e. fluorine doped In2O3, or in a double layer configuration, i.e. IGO covered by SnO2. We have found that the performance of the device depends strongly on the interaction between the surface of the TCO and the US 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 US 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 mum of fluorine doped In2O3 as a TCO. The sputtering atmosphere used for the deposition of this kind of TCO is a mixture of Ar, Ar+H-2 and CHF3. (C) 2003 Elsevier Science B.V. All rights reserved.