photon energy and for any propagation direction. This is essentially the principle of “detailed balance” that has governed solar cell operation for decades. Kirchhoff’s law is, in fact, a consequence of what is called “time reversal symmetry.” One way to bypass the SQ limit is, therefore, to break this symmetry by allowing light to propagate only along one direction. Put simply, the SQ limit can be surpassed if the PV converter absorbs more