Polycrystalline thin films of copper indium diselenide and its alloys with gallium and sulphur (CIGS) have proven to be suitable for use as absorbers in high-efficiency solar cells. Record efficiency devices of 20% power conversion efficiency have been produced by co-evaporation of the elements under high vacuum. However, non-vacuum methods for absorber deposition promise significantly lower capital expenditure and reduced materials costs, and have been used to produce devices with efficiencies of up to 14%. Such efficiencies are already high enough for commercial up-scaling to be considered and several companies are now trying to develop products based on non-vacuum deposited CIGS absorbers. This article will review the wide range of non-vacuum techniques that have been used to deposit CIGS thin films, highlighting the state of the art and efforts towards commercialization.

A chemical method of incorporating copper into indium selenide thin‐films has been investigated, with the goal of creating a precursor structure for conversion into CuInSe2 (CIS) layers suitable for solar cell processing. The precursor and converted layers have been investigated with scanning electron microscopy (SEM), X‐ray diffraction (XRD), Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS). From these measurements, the incorporation of copper into the indium selenide layers is concluded to proceed by an ion‐exchange reaction. This reaction results in the formation of a precursor layer with a graded compositional depth‐profile containing the crystalline phases In2Se3 and Cu2−xSe. Selenisation of the precursor layer homogenises the composition and forms chalcopyrite CIS. These CIS layers exhibit a dense microstructure with rough surface morphology, which is ascribed to a non‐optimal selenisation process. Solar cells with the structure ZnO: Al/i‐ZnO/CdS/CIS/Mo/glass have been processed from the selenised layers and have exhibited efficiencies of up to 4% under simulated AM1·5 illumination. Copyright © 2008 John Wiley & Sons, Ltd.

The effects of different spectra on the laboratory based performance evaluation of amorphous silicon solar cells is investigated using an opto‐electrical model which was developed specifically for this purpose. The aim is to quantify uncertainties in the calibration process. Two main uncertainties arise from the differences in the test spectrum and the standard spectrum. First, the mismatch between reference cells and the measured device, which is shown to be voltage dependent in the case of amorphous silicon devices. Second, the fill factor of the device is affected by different spectra. Different cell structures and states (specifically different i‐layer thickness and levels of degradation) for the different light sources are investigated in this work. These sources are different solar simulators, LED sources, Tungsten as well as the standard terrestrial AM1.5G radiation. It is shown that the performance cannot be evaluated by short circuit current alone. The voltage dependent quantum efficiency of p‐i‐n devices can introduce a mismatch in the PMPP of 1% for 250 nm i‐layer devices in as prepared state, rising to up to 4% for the 600 nm i‐layer devices at degraded state. Copyright © 2011 John Wiley & Sons, Ltd.

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