Roles of surface pattern morphology and sunlight incoherence on solar cell optimization

In order to improve the light absorption efficiency of ultra-thin solar cells, front-side or/and back-side surface texturing are commonly used. This aim is to help coupling incident light into the active layer of the solar cell via light trapping. It has been shown that the morphology of the corrugation pattern has a strong influence on the solar cell efficiency (Herman et al. J Appl Phys 112(11):113107, 2012). However, most of the current optimizations consider that the cell is illuminated under coherent light. This hypothesis is not accurate since the sun is an incoherent source, with a coherence time around 3 fs (Hecht E, Optics, 4th edn. Addison- Wesley, Reading, 2001). Recently, we developed a rigorous theory allowing to take into account the effects of the temporal incoherence of light (Sarrazin et al. Opt Express 21(Suppl 4):A616–A630, 2013). Using this theory we showed that the photocurrent produced by a thin-film solar cell strongly depends on the coherence time of the incident light (Herman et al. New J Phys 16:013022, 2014). Therefore, optimal geometries found under coherent light should be reconsidered because they do not necessarily lead to maximum efficiency under incoherent light.