Optimization of porous silicon reflectance for silicon photovoltaic cells

The antireflection properties of electrochemically formed porous silicon (P S) layers ih the 0.3 mu m thick n(+) emitter of Si p-n(+) junctions, have b een optimized for application to commercial silicon photovoltaic cells. The porosity and thickness of the PS layers are easily adjusted by controlling the electrochemical formation conditions (current density and anodization time). The appropriate PS formation conditions were determined by carrying out a two:steps experiment. A first set of samples allowed to determine the optimal porosity and a second one to adjust the thickness of the PS layers , by evaluating the interference features of the reflectance produced by th e layers. A PS layer with optimal antireflection coating (ARC) characterist ics was obtained in 30% HF in only 3.5 s. The effective reflectance is redu ced to 7.3% between 400 and 1150 nm which leads to a gain of up to 33% in t he theoretical short circuit current of a p-n(+) shallow junction compared to a reference junction without a PS layer. The effective reflectance with optimized PS layers is significantly less than that obtained with a classic al TiO2 ARC on a NaOH pretextured multicrystalline surface (11%). (C) 1999 Elsevier Science B.V. Ail rights reserved.