Nanopatterned Back-Reflector with Engineered Near-Field/Far-Field Light Scattering for Enhanced Light Trapping in Silicon-Based Multijunction Solar Cells

Multijunction solar cells provide a path to overcome the efficiency limits of standard silicon solar cells by harvesting a broader range of the solar spectrum more efficiently. However, Si-based multijunction architectures are hindered by incomplete harvesting in the near-infrared (near-IR) spectral range as Si subcells have weak absorption close to the band gap. Here, we introduce an integrated near-field/far-field light trapping scheme to enhance the efficiency of silicon-based multijunction solar cells in the near-IR range. To achieve this, we design a nanopatterned diffractive silver back-reflector featuring a scattering matrix that optimizes trapping of multiply scattered light into a range of diffraction angles. We minimize reflection to the zeroth order and parasitic plasmonic absorption in silver by engineering destructive interference in the patterned back-contact. Numerical and experimental assessment of the optimal design on the performance of single-junction Si TOPCon solar cells highlights an improved external quantum efficiency over a planar back-reflector (+1.52 mA/cm2). Nanopatterned metagrating back-reflectors are fabricated on GaInP/GaInAsP//Si two-terminal triple-junction solar cells via substrate conformal imprint lithography and characterized optically and electronically, demonstrating a power conversion efficiency improvement of +0.9%abs over the planar reference. Overall, our work demonstrates the potential of nanophotonic light trapping for enhancing the efficiency of silicon-based multijunction solar cells, paving the way for more efficient and sustainable solar energy technologies.

Mask and plate: a scalable front metallization with low-cost potential for III-V-based tandem solar cells enabling 31.6 % conversion efficiency

Low-cost approaches for mass production of III-V-based photovoltaics are highly desired today. For the first time, this work presents industrially relevant mask and plate for front metallization of III-V-based solar cells replacing expensive photolithography. Metal contacts are fabricated by nickel (Ni) electroplating directly onto the solar cell's front using a precisely structured mask. Inkjet printing offers low-cost and high-precision processing for application of an appropriate plating resist. It covers the solar cell's front side with narrow openings for subsequent electroplating. The width of the resulting Ni contacts is as low as (10.5 ± 0.8) µm with sharp edges and homogenous shape. The 4 cm2-sized champion III-V-on-silicon triple-junction solar cell with mask and plate front metallization reaches a certified conversion efficiency η of (31.6 ± 1.1) % (AM1.5 g spectrum). It performs just as well as the reference sample with photolithography-structured evaporated front contacts, which reaches η = (31.4 ± 1.1) %.