Investigation of Texturing for Mono-Crystalline Silicon without IPA

Abstract

Isopropyl alcohol (IPA) is widely used as an additive to enhance the alkaline texturing process of mono-crystalline silicon solar cells currently. However, due to its low boiling point and high volatilization, some negative effects are brought into large scale production especially in stability, cost and environment. In this paper, an IPA-free texturing process was studied by using other additive instead of IPA. The influences of concentration of KOH and additive on etching rate, surface morphology and weighted reflectance were investigated. It is found that the additive has an opposite effect on etching rate and pyramid size compared to KOH. The etching rate and average pyramid size decrease with the concentration of additive increased. The best weight reflectance of 10.8% and lowest average pyramid size of 1.1 um were obtained on mono-crystalline silicon surface by an optimized solution of 1.5 wt% KOH and 1.5 wt% additive at 80oC for 20 minutes. Finally, the effects of KOH and IPA-free additive on the texturing process were also discussed in detail.

Difference in anisotropic etching characteristics of alkaline and copper based acid solutions for single-crystalline Si

“…Usually, upright random sized pyramidal structures 3 , 4 for c-Si and ‘worm like’ structures 5 for mc-Si will be obtained, respectively. More specifically, the texturization of c-Si is usually based on alkali/isopropyl alcohol (IPA) mixture required processing at high temperatures (75 °C–85 °C) for about 20 minutes 3 , 6 , 7 , which had already been commercialized on (100) oriented Si wafers decades ago. It is well-known that each atom of Si {100} surface has two dangling bonds and two back bonds in contrast to one dangling and three back ones for each atom of {111} surface.…”