Note: the talk is based on Guillemoles, Kirchartz, Cahen & Rau, Nat. Phot. 13, 501–5 (2019) & 15,165-6 (2021), and Markvart, Nat Phot., 15, 163-4 (2021):

The Shockley-Queisser model is a landmark in the analysis of light-> electrical energy conversion by the photovoltaic effect, specifically aimed at solar cells. By defining an ideal situation as reference for actual solar cells, upper limits for conversion efficiency are obtained. What is often missed or misunderstood, is that it is a model,  and as such assumptions are made, five of them. If this essential feat of the S&Q work is missed, one gets titles like “breaking the S&Q barrier” which, given that the model is solidly rooted in thermodynamics, should at least raise eyebrows.  By devising a system that does not obey one of the five assumptions, one goes outside the realm of the model.  One can ask, so what? Well, the mode, does encompass most types of solar cells and all the practical ones (without concentration). I will present our guide to help understand and avoid misinterpreting the model, which led to a (published) polemic that shows also has its illuminating aspects about us as scientists. Some comparison with other energy conversion concepts will be made to stress the enormous importance of the S&Q 1961 J. Appl. Phys. paper (rejected at first), which was for decades what is called a sleeping beauty.