Special Issue Non-Vacuum Methods for Formation of Cu(In, Ga)(Se, S) 2 Thin Film Photovoltaic Absorbers C. J. Hibberd 1 * ,y , E. Chassaing 2 , W. Liu 3 , D. B. Mitzi 3 , D. Lincot 2 and A. N. Tiwari 4 1 Centre for Renewable Energy Systems Technology, Holywell Park GX Area, Department for Electronic and Electrical Engineering, Loughborough University, Leicestershire, LE11 3TU, UK 2 Institute of R&D on Photovoltaic Energy (EDF/CNRS/ENSCP-UMR 7174), 6 Quai Watier, 78401 Chatou cedex, France 3 IBM T. J. Watson Research Center, P. O. Box 218, Yorktown Heights, NY 10598, USA 4 Laboratory for Thin Films and Photovoltaics (Abt. 130), EMPA (Swiss Federal Laboratories for Material Testing and Research), U ¨ berlandstrasse 129, CH-8600 Du¨bendorf, Switzerland 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. Copyright # 2009 John Wiley & Sons, Ltd. key words: CIGS; non-vacuum; thin film photovoltaics; CuInSe 2 ; solution deposition; electrodeposition; spray pyrolysis; ink coating Received 11 March 2009; Revised 11 June 2009 INTRODUCTION Although thin-film Cu(In, Ga)(Se, S) 2 (CIGS) solar cells with power conversion efficiencies approaching 20% have been demonstrated, 1 the vacuum-based processes used to deposit the absorber layers in these devices pose cost and technological barriers to the production of low-cost photovoltaic (PV) modules. At present, perhaps the most critical failure is the lack of turn-key CIGS production lines implementing proven processes. This prevents potential cell manufacturers from rapidly tooling up a factory as may be done for c-Si PV. 2 The development of a non-vacuum process for CIGS deposition offers a number of potential advantages over the continued use of vacuum equipment. (1) Developing and commissioning of high-vacuum equipment potentially poses a substantial financial hurdle to enter into the thin film PV market. Uncertainty about the performance (uptime and yield) of new equipment can further increase this barrier, since capital costs and the accompanying depreciation are fixed costs that must be covered PROGRESS IN PHOTOVOLTAICS: RESEARCH ANDAPPLICATIONS Prog. Photovolt: Res. Appl. (2009) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/pip.914 * Correspondence to: C. J. Hibberd, Centre for Renewable Energy Systems Technology, Holywell Park GX Area, Department for Electronic and Electrical Engineering, Loughborough University, Leicestershire, LE11 3TU, UK. y E-mail: c.j.hibberd@lboro.ac.uk Copyright # 2009 John Wiley & Sons, Ltd.