LDK Solar (China)

Metal‐assisted chemical etching (MACE) method is an efficient way to improve the power conversion efficiency of solar cell by developing nanostructures. Normally, hydrogen peroxide is widely used as an oxidizing agent, through which anisotropic etching of nanostructures could be achieved. Here, nanoscale textured multi‐crystalline silicon (mc‐Si) solar cell with an efficiency of 18.13% was fabricated by MACE method with potassium permanganate (KMnO4) as an oxidizing agent. The isotropic etching by KMnO4 showed the great uniformity of surface reflectance, corresponding to the isotropic oval pits. The solar cell presented an increase of 0.72mA · cm−2 in the short‐circuit current density comparing with the mc‐Si solar cell fabricated by the traditional process. Though the efficiency still needed optimizing, isotropic etching for mc‐Si would lead a new tendency for MACE technique.

Physical-chemical characteristics of the band sawing dusts regarding to recovery of pure silicon from them were investigated. The experimental results show 50vol%–60vol% amorphous phases exist in the dusts, which is mostly amorphous silica. The as-received saw dusts are found to form hard agglomerates of larger than 50 microns in diameter. The iron-based inclusions collected by magnets are found to match well with the band saw material in XRD patterns. Weight loss in heating was observed by thermal gravity tests, up to 900 °C, presumably due to reaction of the amorphous silica with carbon contaminant in the dusts. The saw dusts were variously treated to examine their physical-chemical responses, and the results were also presented.

The characteristics of dislocation distribution of a commercially produced multi-crystalline silicon ingot and its influence on cell performance were investigated. The dislocation of a multi-crystalline silicon ingot with a weight of 450kg was measured with the etch pits method. The measurement was made on bricks cut from the corner, the edge, as well as from the center of the ingot. It was found that the dislocation density increases from the bottom to the top and the dislocation density at the top section is at least three times higher than that of at the bottom, while the dislocation density of the corner brick is generally lower than that of the center brick at the same height. The potential influence of such characteristics of dislocation was further investigated through phosphorus gettering process. It was found that the improvement on minority lifetime through gettering is directly related to the dislocation density. The results indicated that the dislocation density is one of the key limiting factors for the performance of mc-Si wafer.

In the industrial production of multicrystalline silicon (mc-Si) wafers used for solar cells, linear wire-sawing defects are sometimes generated on the surfaces of mc-Si wafers. The presence of such wire-sawing defects makes the mc-Si wafers unsuitable for the fabrication of solar cells. In this work, we first studied the nature of the linear wire-sawing defects on the mc-Si wafers, and then investigated how these wire-sawing defects were generated during the wire-sawing process. It has been found that the linear wire-sawing defects are sawing ridges and ditches on the wafer surfaces, and direct evidence has suggested that they are generated due to the presence of SiC particles embedded within mc-Si. The SiC particles form an obstacle to the movement of the sawing wire during the wire-sawing process, and the sawing wire tends to climb over the SiC obstacle, resulting in the generation of the wire-sawing defects. A model for the generation of the wire-sawing defects has been proposed. This work will be of much practical interest to the commercial mc-Si wafer production communities for solar cells.