The time for CIGS

Abstract

This special issue of Progress in Photovoltaics (PIP) is completely devoted to the state of the art in chalcopyrite Cu(In,Ga)(Se,S)2 (CIGS)-based solar cells research and technology. We made the choice to ask for in-depth review papers with joint authorship by scientists from internationally leading research institutions involved in different areas in the field of CIGS solar cells and modules. These invited reviews are devoted to key aspects and specificities of the CIGS photovoltaics (PV) field with an aim to provide to the interested reader a snapshot of the 2010 CIGS's technological landscape and perspectives. The paper from Siebentritt et al. describes fundamental aspects of electronic properties of chalcopyrites and how they are influenced by native defects and grain boundaries. Naghavi et al. summarize the current status of research and development in buffer layers and transparent conducting oxides with special focus of novel and alternative materials and deposition processes. And, influences on solar cell efficiency and metastability are also addressed in this special issue of PIP. While CIGS solar cell technologies based on vacuum deposited absorber layers have driven the advancements with the highest efficiency records and heading towards industrial maturity, the non-vacuum processes are drawing considerable attention because of the attractive inherent features related to large area scale up and low cost processing. Hibberd et al. provide a comprehensive review of various deposition methods and current status of this approach for the fabrication of CIGS solar cells. On the other hand, the review paper from Niki et al. is focused on solar cell and module technologies based on vacuum deposited absorber layers describing aspects of manufacturing and performance stability. The topics of process monitoring and control are very important for the development of reproducible manufacturing processes and also to enhance the production yield. Scheer et al. provide a critical assessment of various techniques and tools to study fundamental physical properties of CIGS PV materials and solar cells with special emphasis on the application of laser light scattering, Raman scattering and time resolved photoluminescence. Editors accept that some important topics might be missing and could have been addressed, and also contributions from several other leading groups could have further enhanced the value of the special issue. By the way the special issue comes timely in a key transition period for PV, not only regarding the global acceleration of the growth of PV production towards large scale deployment in the near future, but also strengthening the position of thin film PV technologies with respect to traditional wafer-based silicon PV. At the beginning of the decade, the share of thin film PV, mostly a-Si based, was decreasing in relative value, from 12.5% in 2000 to 6% in 2005, giving the impression that contrary to the expectations thin film technologies will not become competitive. However, 2005 saw the start of large scale industrial commercial development of thin film CdTe with ever growing success in increasing production volume and decreasing production costs to the ‘benchmark value of below one dollar’ for the first time. Thin film PV production is increasing in volume as well as in terms of relative contribution to the global PV production with an incredibly high growth rate. In 2009, a CdTe thin film company became for the first time in PV history the number 1 in the field: who would have expected this revolution? After 30 years of R&D, the ‘potential’ of chalcogenide compound semiconductors had finally been demonstrated! But this may be only the beginning of the success story for chalcogenide materials. As in the case of CdTe, CIGS has progressed step by step, reaching an incredible level of efficiency of 20% while the industrial production of CIGS modules crossed the symbolic value of 1% in market share in 2008. Does it means that CIGS share will be of 9% within 4 years of the total PV production? Maybe yes, many indicators point that way, but one thing is certain: CIGS technology is here to stay and will successfully contribute to the solar revolution. We hope that this special issue, giving an example of very dynamic worldwide research networks and collaborations, will be useful for making this challenge a reality. It is the right time for CIGS!