Microsol International’s researchers investigate fabrication process of textured wafers.

Stable texturization process by carbohydrates

Stable texturization: Photovoltaic industries widely use the standard texturization method with NaOH/KOH and IPA (Isopropyl alcohol) to reduce reflectivity of monocrystalline silicon ( crystal orientation) wafers. IPA promotes the formationof uniform pyramidal structure but leads to unstable process. In this work, MicrosolInternational’s Md. Al-Amin, A.K.M. Rahmatul Alam, Kiran Turlapati and Barath Baskaranathan have investigated carbohydrates as an additive in the etchant solution. It has no evaporation loss and thus leads to a stable process.

The etching rates of different concen-trations of carbohydrates, surface mor-phology, reflectance factor and processstability were analyzed. A batch of 156Pseudo-Square mono c-Si solar cells with17.1 to 17.2 percent efficiencies was fabri-cated with new texturization additiveand compared with standard cells. This technology is yet to be incorporated into Microsol’s production lines.

Introduction

In the commercial solar cell process, oriented single crystal silicon wa-fers are used for texturization and appro-priate ARC (anti-reflective coating) to re-duce reflection. After removing the sawdamage, the wafer’s reflection of incident light is more than 35 percent [Tom Mark-vart, Luis Castaner, Solar Cells Material,Manufacturing and Operation; Elsevier,2005]. Sodium hydroxide (NaOH) andpotassium hydroxide (KOH) are well-rec-ognized etchants of silicon. Typically the etching rate depends on the process time,temperature and concentration of the so-lution. The surface development duringetching depends on the reaction mechanism, which is not fully understood indetail. The following chemical reactions during the etching process are generallyaccepted.

Si+H2O+2NaOH→Na 2SiO3+2H2↑

Si+H2O+2KOH→K 2SiO3+2H2↑

The etching rate needs to be controlledin order to get selective etching. Pyramidformation will not take place without an additive because of poor wettability of thesilicon surface that leads to insufficientpyramid nucleation [U. Gangopadhyay,K. Kim, A. Kandol, J. Yi, H. Saha, Role of hydrazine monohydrate during textur-

2010 has been a year of ever reducing cost and one of the key contributors to reducing this gap has been our R & D activity. The focus as always is on achieving higher and higher efficiencies but now it also has equivalent pressure in continually reducing the costs involved in the conversion of wafers to cells.

In 2011, Microsol has plans to scale to great heights in both Cell Technology as well as Module Technology.  To make these plans into realities Microsol’s R&D team is working in cooperation with well reputed research  institutes from across the industry.Some of the major improvements being looked at to achieve our efficiency targets are changes to the designs of our Cells and Modules. On the other hand to achieve our cost goals Microsol is looking at pushing higher and higher with its yields.One of the prime focus issues for this year that will allow Microsol to differentiate from its competitors is: the improvement of the total energy generated in a solar installation when using a module made with Microsol solar cells.