TMAH-textured, a-Si/c-Si, heterojunction solar cells with 10% reflectance

Single-polished c-Si (1 0 0) wafers were textured in aqueous solutions with varying concentrations of tetra-methyl ammonium hydroxide (TMAH). The resulting surface reflectance and morphology were examined as a function of etching time and temperature, TMAH concentration, and addition of isopropyl alcohol to the solution.The lowest reflectance, 9.8% at a 600-nm wavelength with 0.3% scattering over a 4″ wafer surface, was obtained after 40 min of etching in a 2% TMAH solution at 80 °C under 700 rpm magnetic stirring. Upon adding isopropyl alcohol to the solution, the resulting pyramids were round-edged, and 12% sample reflectance was obtained.The results are interpreted in terms of micro-masking formation and temperature-dependent crystallographic selectivity.The compatibility of the treatment with photovoltaic applications was evaluated by studying the performance of heterojunction solar cells, which are particularly sensitive to surface quality. A degradation of the open circuit voltage was observed in devices fabricated on surfaces featuring crooked pyramid sides. Optimised process conditions led to smooth pyramid sides and no degradation of the open circuit voltage, which indicates no sign of increased surface recombination-centre concentration. The reduced reflectance resulted in a 16% increase of the short circuit current of the solar cell device.

Surface morphologies of c-Si wafers textured using different TMAH based solutions. Solar cell parameters of heterojunctions fabricated on the three substrates.Figure optionsDownload as PowerPoint slideHighlights
► We performed texturing of crystalline silicon by tetra-methyl ammonium hydroxide.
► We compare reflectance and surface morphology resulting from different conditions.
► The lowest reflectance achieved is 9.8% with ±0.3 % homogeneity.
► Heterojuction solar cells are fabricated on wafers with different morphology.
► The best substrate for heterojunctions is covered by pyramids with smooth faces.