Texturization of multicrystalline silicon by wet chemical etching for silicon solar cells

Abstract

Two kinds of surface texturization of mc-Si obtained by wet chemical etching are investigated in view of implementation in the solar cell processing. The first one was the acid texturization of saw damage on the surface of multicrystalline silicon (mc-Si). The second one was macro-porous texturization prepared by double-step chemical etching after KOH saw damage layer was previously removed.

Both methods of texturization are realized by chemical etching in HF-HNO₃-H₂O with different additives. Macro-porous texturization allows to obtain effective reflectivity (R_eff) in the range 9–20% from bare mc-Si. This R_eff value depends on the time of second step etching that causes porous structure modification. The internal quantum efficiency (IQE) of cells with this kind of texturization has possibility to reach better conversion efficiency than the standard mc-Si solar cells. However, low shunt resistance depends on morphology of porous layer and it is the main factor which can reduce open circuit voltage and conversion efficiency of cells.

The effective reflectivity is about 17% for acid texturized mc-Si wafer. The investigation of surface morphology by scanning electron microscopy (SEM) revealed that the dislocations are appearing during chemical etching and they can reduce open circuit voltage. The density of the dislocations can be reduced by controlling depth of etching and optimisation of acid solution.