Prediction of defective regions in optimisation of surface textures in thin-film silicon solar cells using combined model of layer growth

• Growth model used to predict defective regions within thin-film solar cells
• Influence of the shape of surface textures on occurrence of defective regions shown
• Smoothening/widening of the valleys is not always beneficial.
• Optical optimisation with consideration of defective regions was performed.
• Semi-circular texture is determined to have high potential for defectless growth.

In this paper previously developed combined model of non-conformal layer growth is used to calculate positions in thin-film silicon solar cells where defective regions are expected to be formed within semiconductor layers, depending on the substrate texture. This enables omission of the textures leading to cells of poor electrical quality in the early process of optical optimisation of the cells and substrate texture design. Coupled with three-dimensional rigorous optical simulations, substrate textures are optimised with respect to high short-circuit current and defectless layer growth in micromorph silicon solar cells. Firstly, the approach of determination of defective regions is validated on realistic structures. Secondly, analysis of the effects of texture shape and of the material and the thickness of the grown layer is carried out. Thirdly, optimisation of substrate texture for micromorph type of solar cell is performed for sinusoidal, widened and semi-circular textures. Results on widened textures show, that smoothing/widening of the valleys does not always suppress the formation of defective regions in μc-Si:H and a-Si:H layers. A semi-circular type of the texture is determined to be the most appropriate for defectless absorbers in the analysed micromorph solar cells in substrate configuration, resulting also in up to 85% increase in short-circuit current of the bottom cell.