Spatial coherence of sunlight and its implications for light management in photovoltaics

New technologies are emerging that capture and redirect sunlight inside solar cells. This type of light management can significantly increase efficiency, but the device behavior will fundamentally depend on the spatial coherence of the incoming light. This dependence calls for a complete characterization of the spatial coherence of sunlight. Here, we present the first spectral measurements of the spatial degree of coherence of direct, diffuse, and simulated sunlight. An expression is derived for both the cross-spectral density and the spatial degree of coherence in an arbitrarily oriented device plane, including the effects of overcast skies. Implications of the present work are discussed and may lead to a better understanding of light-managing components in solar cells as well as a new class of solar simulator that provides both the same spectrum and spatial coherence as direct sunlight.