Efficiency enhancement of crystalline silicon solar cells by coating with luminescent silicon nanostructures

In this work we report a technique that is potentially capable of increasing the efficiency of crystalline silicon solar cells, which dominate the present day market of photovoltaic devices. The simple and cost-effective method involves coating the surface of a commercially procured silicon solar cell with a thin layer of luminescent silicon nanocrystals. Core/shell silicon/silicon-oxide nanostructures are fabricated by an inexpensive and reproducible technique, where commercially obtained coarse silicon powders are repeatedly milled, oxidized and etched till their sizes are reduced so as to exhibit room temperature photoluminescence under ultraviolet excitation. We observe that the thickness of the layer of nanostructures plays a significant role and the enhancement can be obtained only for certain optimal thickness. Although, we are yet to devise a strategy to control this thickness, we find that for some optimal thickness the open circuit voltage (Voc) and the short-circuit current (Isc) increases by 13% and 16.5% respectively for the cells coated with silicon nanostructures which consequently increases the maximum power delivered by the cell by ∼14.6%. From the spectral response study we see that that the increments in Voc and the Isc are maximum in the UV-blue region. Based on these exciting initial findings we suggest that the luminescent Si nanostructures are acting as luminescence converters thereby accounting for the observed enhancement.