S-Q Guide for the Perplexed 10-10-2018 1 Solar Energy Conversion and the Shockley-Queisser Model, a Guide for the Perplexed Jean-Francois Guillemoles 1 , Thomas Kirchartz 2,3 , David Cahen 4 , and Uwe Rau 2 1 CNRS, UMR 9006, Institut Photovoltaique d’Ile de France (IPVF), Palaiseau, France 2 IEK5-Photovoltaik, Forschungszentrum Jülich, 52425 Jülich, Germany 3 Fac. of Engineering and CENIDE, Univ. of Duisburg-Essen, Carl-Benz-Str. 199, 47057 Duisburg, Germany 4 Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel e-mails for correspondence: Jean-Francois.GUILLEMOLES@cnrs.fr ; david.cahen@weizmann.ac.il ; t.kirchartz@fz-juelich.de; u.rau@fz-juelich.de Abstract The Shockley-Queisser model is a landmark in photovoltaic device analysis by defining an ideal situation as reference for actual solar cells. However, the model and its implications are easily misunderstood. Thus, we present a guide to help understand and avoid misinterpreting it. Focusing on the five assumptions, underlying the model, we define figures of merit to quantify how close real solar cells approach each of these assumptions. Introduction In 1961 Shockley and Queisser 1 (SQ) analyzed the limits of photovoltaic energy conversion, using the basic thermodynamic principle of detailed balance instead of phenomenological approaches, used earlier. 2-4 The final result of their analysis is commonly referred to as the ‘SQ- limit’. While arguably the most important theoretical contribution to photovoltaic energy conversion, the paper also relies on a highly idealized model for solar cells, using substantially simplifying assumptions. Therefore, only within the assumptions of their model (denoted the SQ-model in the following) does the term ‘SQ-limit’ make sense. In view of the emergence of promising new photovoltaic absorber materials and devices with very high efficiencies 5 with various claims of ‘exceeding or approaching the SQ-limit’, 6,7 we will critically discuss the connection of the SQ-model to real world solar cells and will explain what ‘close’ to the SQ- model means. First, we briefly describe the SQ-model in its initial form by illustrating its three fundamental steps, noting the energy losses associated with each of these. We then describe the five assumptions that are the essence of the model (Table 1). Subsequently, we examine how each of these assumptions compares to more realistic situations, discuss experimentally