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This issue of physica status solidi (a) contains selected papers which represent currently running activities related to silicon-based photovoltaics (PV). Since the topic of Si based PV is very broad, the definition of “advanced concepts” is, in fact, not well defined and, in general, can be attributed to any of the activities, which: (i) can improve existing Si based solar cells; (ii) generate novel concepts, which can reduce cost of Si based PV dramatically; (iii) permit to overcome the fundamental efficiency limits. Silicon as well as advanced silicon based materials and structures are in the center of modern PV and will remain as the central part of the advanced research in this field for decades. Fundamental as well as technological developments dealing with Si material in the form of wafers, thin films (both types, crystalline and amorphous), nanowires and nano-dots are in center of currently running activities worldwide. Being a low-cost feedstock, silicon remains the dominating material for the photovoltaic industry, and most probably will keep this role in a long term perspective, as soon as PV is targeting the terawatt range. Although there are a number of different thoughts and statements concerning the post-Si wafer era, at the present state it is not clear which technology and which advanced Si based structures can compete with the Si wafer based approach on industrial level. At the current stage it is still necessary to clarify whether or not any advanced concept which is dealing with the implementation of advanced Si based materials can be useful for future large scale PV, or problems such as passivation, processing cost, degradation, mechanical stability, etc. will prevent implementation of most of the advanced concepts and materials. Although the main part of any Si based solar cell structure is silicon itself, a number of other advanced materials have to be implemented in order to “assist” silicon in any type of Si based solar cell structure to make such structure working efficiently. Therefore, in addition to contributions dealing with Si material related developments, some selected articles devoted to other than Si materials, which are useful for advanced Si based PV, have been included in this issue as well. These other materials, being implemented into advanced Si based structures, can provide better conditions for light trapping, collection of current, etc. Typical examples of such materials are transparent conductive oxides (TCOs) and silicon nitrides. Therefore, in this issue, topics ranging from fundamental research of some PV-specific physical phenomena to a number of advanced materials and Si based solar cell structures have been covered. The majority of contributions has been selected on the basis of presentations which were given at the Open Workshop “Advanced Concepts in Silicon Based Photovoltaics” (Oslo, Norway, June 20–22, 2012, www.sintef.no/acpv). This Open Workshop was organized for the participants of the following EU FP7 program PV related projects: Hipersol, ThinSi, R2M-Si and nanoPV. Moreover, several other relevant EU projects (NanoSpec, SNAPSUN, NASCEnT, PolySiMode, RodSol, Sugar) have been involved and some of them contributed to this special issue. Several contributed articles represent Si based PV related activities in research groups which are not directly involved in the EU funded PV projects developments. Financial support from the EU Commission, which made possible the preparation of most of the contributions for this special issue, is gratefully acknowledged.

Alexander Ulyashin

Guest Editor

SINTEF Materials and Chemistry, Oslo, Norway