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Introducing thin, light-weight and high efficiency photovoltaics will make solar cells more suitable to be integrated in urban landscapes or even small gadgets and would largely contribute to solving the global warming threat that we are facing today. Stacking of solar cells with different characteristic bandgaps is the most common strategy to surpass the Shockley-Queisser efficiency limit, but such tandem devices are typically heavy weight, rigid and costly. Thinning down of absorber materials is a good strategy to overcome these restrictions. However, nano- and micro-meter thicknesses come down to the expense of light absorption. An effective approach to tackle the absorption problem in thin materials is nanopatterning the absorbing layer.
In this work we introduce hyperuniform designs as an effective way to control scattered light into particular range of angles (revealed as a ring in k-space of the reflected/transmitted light), with the aim to efficiently trap light in μm-thick Silicon (Si) cells. We first consider the –theoretical and experimental- case of a single Si solar cell, and thanks to an optimization algorithm, we show the highest light absorption in 1 μm-thick Si film to date. We also compare different designs for best anti-reflection effect on top of light trapping and characterize the increased absorption in photoelectrochemical devices. Second, we incorporate a similar light trapping strategy in a tandem solar cell, by using a periodic GaAs nanowire array as a top cell. We introduce two waveguiding effects in GaAs NW-Si thin film architectures to explain the 4-fold light absorption in the Si ultrathin bottom cell for tailored geometries of the NW array. These results represent significant light trapping scheme that is obtained “for free” when using a nanostructured top cell.
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