Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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IEEE Journal of Photovoltaics, Volume 8, issue 3
Black silicon (b-Si) has been estimated to considerably grow its market share as a front texture of high-efficiency silicon solar cells. In addition to excellent optical properties, high-efficiency cell process requires extreme cleanliness of the bulk material, and thus cleaning of b-Si surfaces is often a critical process step. While standard clean (SC) 1 solution efficiently removes possible contamination from wafer surfaces, we show here that it may cause challenges in b-Si solar cells. First, the silicon etch rate in SC1 solution is shown to depend on the phosphorous concentration and as high rate as ∼1.4 nm/min is observed on planar emitter surfaces. When extending the study to b-Si, which has much larger surface area in contact with the cleaning solution, even higher volumetric Si consumption occurs. This is observed in significant changes in emitter doping profiles, for instance, a 10 and 30-min cleaning increases the sheet resistance from 47 to 57 Ω/□ and 127 Ω/□, respectively. Furthermore, the SC1 solution alters substantially the nanostructure morphology, which impacts the optics by nearly doubling and more than tripling the surface reflectance after a 30 and 60-min immersion, respectively. Thus, uncontrolled cleaning times may impair both the electrical and optical properties of b-Si solar cells.
black silicon, etching, nanostructure, phosphorus emitter, RCA clean, standard clean
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Pasanen , T P , Laine , H , Vähänissi , V , Salo , K , Husein , S & Savin , H 2018 , ' Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon ' , IEEE Journal of Photovoltaics , vol. 8 , no. 3 , pp. 697-702 .