Record efficiencies for dry processed cadmium free CIGS solar cells with indium sulfide buffer layers prepared by atomic layer deposition (ALD)

CIGS based solar cells are presently excellent candidates for a new generation of large scale and low-cost photovoltaic thin film modules. To allow exclusively vacuum processing, a dry alternative for the buffer layer deposition is desirable. For environmental reasons, it is also desirable to get Cd-free devices. Atomic layer chemical vapor deposition (ALCVD or ALD) is a technique ensuring conformal growth of thin films from the vapor phase in a scalable manner. This paper presents optimization studies on the formation of In/sub 2/S/sub 3/ buffer layers by ALD for high efficiency CIGS thin film solar cells. The main parameters investigated are the deposition temperature (between 150 and 260/spl deg/C) and the effect of the thickness of the buffer (15 nm and 30 nm), on growth rates, properties of the films and solar cells parameters. The highest efficiency of 16.4% has been obtained at 220/spl deg/C for a layer thickness of 30 nm. Diffusion of copper and sodium has been evidenced by XPS measurements which may have a positive role in the junction formation processes. The importance of interface chemistry for dry buffer is underlined.