Browsing by Author "Salmi, Emma"

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AlOx surface passivation of black silicon by spatial ALD: Stability under light soaking and damp heat exposure
(2020-03-01) Heikkinen, Ismo T. S.; Koutsourakis, George; Virtanen, Sauli; Yli-Koski, Marko; Wood, Sebastian; Vähänissi, Ville; Salmi, Emma; Castro, Fernando A.; Savin, Hele
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Scientific breakthroughs in silicon surface passivation have enabled commercial high-efficiency photovoltaic devices making use of the black silicon nanostructure. In this study, the authors report on factors that influence the passivation stability of black silicon realized with industrially viable spatial atomic layer deposited (SALD) aluminum oxide (AlOx) under damp heat exposure and light soaking. Damp heat exposure conditions are 85 °C and 85% relative humidity, and light soaking is performed with 0.6 sun illumination at 75 °C. It is demonstrated that reasonably thick (20 nm) passivation films are required for both black and planar surfaces in order to provide stable surface passivation over a period of 1000 h under both testing conditions. Both surface textures degrade at similar rates with 5 and 2 nm thick films. The degradation mechanism under damp heat exposure is found to be different from that in light soaking. During damp heat exposure, the fixed charge density of AlOx is reduced, which decreases the amount of field-effect passivation. Degradation under light soaking, on the other hand, is likely to be related to interface defects between silicon and the passivating film. Finally, a thin chemically grown SiOx layer at the interface between the AlOx film and the silicon surface is shown to significantly increase the passivation stability under both light soaking and damp heat exposure. The results of this study provide valuable insights into surface passivation degradation mechanisms on nanostructured silicon surfaces and pave the way for the industrial production of highly stable black silicon devices.
Industrial Applicability of Antireflection-Coating-Free Black Silicon on PERC Solar Cells and Modules
(2018) Pasanen, Toni; Vähänissi, Ville; Wolny, Franziska; Oehlke, Alexander; Wagner, Matthias; Juntunen, Mikko A.; Heikkinen, Ismo T. S.; Salmi, Emma; Sneck, Sami; Vahlman, Henri; Tolvanen, Antti; Hyvärinen, Jaakko; Savin, Hele
A4 Artikkeli konferenssijulkaisussa
Black silicon (b-Si) is of particular interest within the photovoltaic community due to its ability to texture diamond wire-sawn multicrystalline silicon wafers. In this work, we apply a deep dry-etched black silicon nanotexture, which possesses less than 1 % solar-weighted reflectance with no antireflection coating (ARC), to industrial Passivated Emitter and Rear Cells (PERC). Additionally, the cells are processed further into small solar modules, which are characterized by their electrical and optical performance. The fragile nanostructures remain intact during industrial cell and module fabrication, maintaining the excellent optical properties until the final product. We show that b-Si modules with a typical cover glass retain their performance until incident angles larger than 60°, whereas the heavily increased reflectance of acidic-textured modules decreases their efficiency already after a 30° tilt. Furthermore, at an incidence angle of 70°, the efficiency of b-Si modules has reduced only 7 %, while that of the acidic-textured equivalents has decreased more than 25 %. Hence, the excellent optical properties of ARC-free b-Si are maintained also at module level. The results demonstrate that deep dry-etched b-Si nanostructures are fully applicable to current industrial PERC production facilities.