Arrays of nano and micro inverted silicon structures via copper catalyzed chemical etching for effective light trapping

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Nano/micro structuring of silicon (Si) via chemical approaches have currently acquired a lot of research interests owing to their excellent light trapping abilities in broad spectral range. Here, a comprehensive study on the fabrication of nano/micro-inverted structures via one-step copper (Cu) catalyzed chemical etching (CuCCE) of solar grade n-Si wafers employing the aqueous solution of Cu(NO3)2/HF/H2O2 in various compositions and their light trapping ability are reported. Influence of etch parameters, namely, Cu2+ ions concentration, HF/H2O2 compositions and surface properties of the wafers are systematically investigated on the evolution of different inverted nano- and micro-structured Si surfaces. Arrays of micron-sized inverted pyramids (μ-IP) and nano-micro-hybrid inverted pyramids (n-μ-HIP) have been fabricated on partial polished and as-cut solar grade Si wafers respectively in an optimized compositions of the solution (Cu(NO3)2, HF and H2O2 at 5 mM, 4.6 M and 0.55 M respectively) at 50 °C after 15 min. The surfaces exhibit solar weighted reflection as low as <7% and <5% respectively for a broad spectral range (400–1000 nm; AM1.5G). The n-μ-HIP-Si arrays also exhibited ∼8 fold enhanced Raman signal. Isotropic thinning of Si wafers, nano-porous, and craters like Si structures could also be obtained under appropriate etch conditions. Mechanism of the formation of such inverted structures under different etch conditions have been explained based on the Cu catalyzed, self-controlled electrochemical redox reactions and balancing act of anisotropic-isotropic etching of Si in the CuCCE etch bath. The excellent light trapping properties of the nano/micro structures is also explained. Moreover, the ‘proof of concept’ of application of the inverted nano/micro light trapping structures in the PEDOT:PSS/n-Si hybrid heterojunction solar cells with enhanced performance has also been shown. The Si surfaces via simple yet effective CuCCE process may find applications in other photosensitive devices as well as surface enhanced Raman spectroscopy.