Differences in etching characteristics of TMAH and KOH on preparing inverted pyramids for silicon solar cells

In this paper, a series of comparative etching experiments on preparing inverted pyramids of silicon solar cells have been carried out using tetramethyl ammonium hydroxide (TMAH) and potassium hydroxide (KOH) at different etchant concentrations and temperatures on a patterned (1 0 0) Si. These experiment results show that TMAH solution has higher undercut rate and lower (1 0 0) plane etch rate than KOH solution, and the (1 1 1)/(1 0 0) etch rate ratio of TMAH is two to three times that of KOH solution. Additionally, etch rate of SiO2 mask is an order of magnitude lower in TMAH than in KOH. Besides, surface morphology analysis indicates that TMAH etching can obtain much higher quality inverted pyramids of sharp vertex, smooth (1 1 1) sidewall and uncontaminated surface than KOH etching, which makes TMAH etching samples show better antireflection properties. Finally, the minimum reflectivity of TMAH etching sample low as 1.8% is obtained for inverted pyramids covered with SiO2 reflectivity coating. So the study reveals that TMAH is more attractive for the preparation of inverted pyramids than KOH.