Ultra-Thin and Ultra-Light Si Solar Cells with Hyperuniform Disordered Light Trapping

<br/>Ultra-thin crystalline silicon solar cells could, in contrast to their thick counterparts, simultaneously reduce levelized cost of electricity by a large factor and be deployed on curved or non-static surfaces, windows, as well as facilitate building integrated photovoltaics. Moreover, their light weight, integrability into systems or tandem devices, and robustness to (cosmic) radiation also renders them excellent candidates for space applications. Silicon at micron-scale thickness, however, suffers from poor light absorption and conventional light trapping approaches such as random KOH texturing fails due to the feature sizes produced.<br/>We present hyperuniform disordered (HUD) light-trapping structures applied to ultra-thin solar cells via substrate-conformal imprint lithography. This approach enables rapid patterning of large areas (m2) at the nanoscale and can be performed on virtually any substrate and for any type of functional layer, such as the absorber, back-reflector, anti-reflection coating or carrier transporting layers. Correlated-disorder structures were shown to outperform periodic as well as random light trapping approaches [1] and the hyperuniform platform in addition offers tailored scattering to engineer light coupling to guided modes of ultra-thin absorbing layers [2]. To this end, we developed a coupled-mode theory (CMT) approach for estimating absorption with HUD patterns of arbitrary power spectral density distributions, which affords optimizations at low computational effort. CMT predictions are validated by determining the in-coupling rates per guided mods for different HUD designs, which we achieve through FDTD simulations. Furthermore, we show experimentally measured absorption in ultra-thin, free-standing, hyperuniform-patterned silicon slabs of thicknesses ranging from 1-30µm and compare with simulations.<br/>Finally, we show the performance of ultra-thin Si solar cells before and after the application of HUD light trapping structures.<br/>In conclusion, our work exploits stealthy hyperuniformity for exceptional light trapping and aims to further expand the success of earth-abundant silicon to ultra-thin, flexible, semi-transparent, airborne, and off-planet PV devices, which can be produced with kerfless bottom-up technologies at significantly reduced capex and accompanying CO2 emissions while maintaining high power conversion efficiencies – A type of device that could literally pave all roads, roofs, walls, windows, and spacecraft by 2050!<br/> <br/><b>Publication</b><br/>N. Tavakoli et al., “Over 65% Sunlight Absorption in a 1 μm Si Slab with Hyperuniform Texture”<i>,</i><i> ACS Photonics 2022, 9, 4, 1206–1217</i>, DOI: 10.1021/acsphotonics.1c01668<br/> <br/><b>References</b><br/>[1] Bozzola et al. (2014). Broadband light trapping with disordered photonic (..). <i>Prog. Photovolt: Res. Appl., 22, 1237– 1245</i>. <br/>[2] Florescu et al. (2009). Designer disordered materials with large, complete photonic band gaps. <i>PNAS, 106(49), 20658-20663</i>.