- We present experimental evidence for improving the open-circuit voltage–and thereby efficiency-of photovoltaics via the external recycling of photon emission. This strategy is equivalent to limiting the angular extent of photon emission-effective only in photovoltaics with high external luminescent efficiency. This is why the effect has not been observed in current solar cell technologies. It is attainable with the latest generation of ultra-efficient single-junction non-concentrator thin-film GaAs cells. The findings are explained in terms of basic photovoltaic thermodynamics.