Single-step fabrication of single-junction c-Si nano-structured solar cells by optimization of plasma etching parameters

Abstract

The production cost of photovoltaic solar cells could be reduced by minimizing the number of fabrication steps, e.g., eliminating separate stages of assembling p-layer, n-layer and anti-reflection coating layer. The uniqueness of the present work remains in the single step growth of the n-layer and the simultaneous anti-reflection coating layer via plasma etching of the p-type crystalline silicon (p–c-Si) wafers by low pressure inductively coupled plasma (ICP) CVD system. Chemical and physical etching of the p–c-Si wafer by high density of atomic H and ionic Ar/H species in the (Ar + H2) plasma create surface-roughness that introduce reduced surface reflectance. Further, ejection of Si moieties from the wafer surface produces SiHX (x = 1–4) radicals in the plasma, which in turn instigate re-deposition at the dangling c-Si bond sites and produce variety of silicon nanostructures (Si-NSs). The etching and sequential redeposition effects occur differently on varying gas ratio of Ar/H2, changing plasma pressure and etching temperature. At optimized low pressure (∼100 mTorr) in the plasma crystalline silicon nano-pillar like structures of uniform diameter, length and alignment are produced, from which multiple internal reflections result efficient light trapping and a significantly low reflection loss. Further, the plasma deposited Si nanostructures on the etched p-type c-Si wafer surface changes to n-type in electronic configuration, grown via p-to-n type conductivity conversation (PTNCC) process, initiated by alteration in BH1 bonds to BH2 and/or BH3 configurations. The p-n junction solar cells spontaneously grown via PTNCC mechanism demonstrates a proof-of-concept conversion efficiency, η ∼4.22%, using ITO layer at the front and silver (Ag) paste as the back electrodes.