Effect of diffusion doping-induced defects on shunt resistance affecting Si-nanowire solar cell performance

Si nanowires (SiNWs) are preferred over bulk Si for photovoltaics owing to near-zero optical reflection and band gap tunability. However, the cost-effective fabrication of phosphorus-doped SiNWs poses challenges. The work employs metal-assisted chemical etching for SiNW array fabrication and spin-on doping with P₂O₅ as the phosphorus source to form an n-type emitter. The P₂O₅ concentration in the phosphosilicate glass (PSG) sol–gel controls the phosphorus-doping level on the SiNWs. Morphological analysis detects a marginal reduction in the SiNW lengths with P₂O₅ concentration after PSG layer removal. The optical studies show a significant decrease of the average reflectance to 3.99% and a band gap of 1.59 eV for the optimized doping density (fabricated with a P₂O₅ concentration of 5 mM), leading to a 34.5% improvement in the ultimate efficiency. Raman asymmetric ratio and photoluminescence emission spectra elucidate the possible surface and bulk defects causing the recombination. The resistivity of the optimized phosphorus-doped SiNW array decreases to 3.37 Ω cm due to a significant increase in the donner concentration. The study compares various methods to estimate the internal cell resistances from the illuminated current–voltage measurement and considers the single-diode model accurate. The power conversion efficiency and the fill factor of the optimized solar cell are 4.09% and 43.4%, respectively, limited by the increased series resistance and decreased shunt resistance.