Relation between solar cell efficiency and crystal defect etching induced by acidic texturization on multicrystalline silicon material

Acidic texturing of multi crystalline silicon (mc-Si) wafers often leads to rough surfaces with areas of strong etch attacks which we call trench structures. Particularly at sites containing crystal defects such as grain boundaries and dislocations, trench structures are created. These trench structures have often been reported as detrimental to solar cell performance. In this paper, a detailed statistical analysis of the influence of trench structures on solar cell efficiency is carried out. It is shown that their influence on cell efficiency, as well as open circuit voltage, short circuit current and fill factor, is only very minor. The material quality determines the diffusion length of the minority carriers and predominantly impacts the solar cell efficiency. Moreover, it has been established that trench structures do not significantly influence surface roughness and do not lead to shunting losses. However, the statistical model indicates that materials with many crystal defects, and thus lower quality and a smoother (and hence more reflecting) texture lead to slightly higher efficiencies compared to solar cells with a rougher texture. The higher efficiency obtained with smoother textures for this kind of material might be caused by the absence of trench structures. Furthermore, it has been found in this work that for these acidic textures, surface roughness correlates to weighted reflection and hence only one of these parameters has to be determined to analyze an acidic texture.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Acidic texturing leads to strong etch attacks (trench structures) at crystal defects. ► Trench structures are often regarded as harmful for solar cell performance. ► In this work a detailed statistical analysis on the impact of trench structures on solar cell efficiency is presented. ► It shows that the influence of trench structures is only very minor. ► With bad material quality a more reflecting and hence trench-structure avoiding texture yields better efficiencies.