ABSTRACT Maximum possible photovoltaic performance is reached when solar cells are 100% radiatively efficient, with different photovoltaic technologies at different stages in their evolution towards this ideal. An external radiative efficiency is defined, which can be unambiguously determined from standard cell efficiency measurements. Comparisons between state‐of‐the‐art devices from the representative cell technologies produce some interesting conclusions. Copyright © 2011 John Wiley & Sons, Ltd. Maximum possible photovoltaic performance is reached when solar cells are 100% radiatively efficient, with different photovoltaic technologies at different stages in their evolution towards this ideal. An external radiative efficiency is defined, which can be unambiguously determined from standard cell efficiency measurements. Comparisons between state‐of‐the‐art devices from the representative cell technologies produce some interesting conclusions.