Black Ultra-Thin Crystalline Silicon Wafers Reach the 4n² Absorption Limit-Application to IBC Solar Cells

Cutting costs by progressively decreasing substrate thickness is a common theme in the crystalline silicon photovoltaic  industry for the last decades, since drastically thinner wafers would significantly reduce the substrate-related costs. In addition to the technological challenges concerning wafering and handling of razor-thin flexible wafers, a major bottleneck is to maintain high absorption in those thin wafers. For the latter, advanced light-trapping techniques become of paramount importance. Here we demonstrate that by applying state-of-the-art black-Si nanotexture produced by DRIE on thin uncommitted wafers, the maximum theoretical absorption (Yablonovitch's 4n² absorption limit), that is, ideal light trapping, is reached with wafer thicknesses as low as 40, 20, and 10 µm when paired with a back reflector. Due to the achieved promising optical properties the results are implemented into an actual thin interdigitated back contacted solar cell. The proof-of-concept cell, encapsulated in glass, achieved a 16.4% efficiency with an J_SC  = 35 mA cm^{- 2} , representing a 43% improvement in output power with respect to the reference polished cell. These results demonstrate the vast potential of black silicon nanotexture in future extremely-thin silicon photovoltaics.