Texturization control for fabrication of high efficiency mono crystalline si solar cell
We studied the texturization mechanism of mono crystalline silicon wafer using some alternative additives. We successfully controlled the texture size with change of concentration of KOH in the etchant. We also proposed one appropriate model of role of additives in texturization process. In our proposed mechanism, the additives should play a role as micro-mask when the micro pyramid is formed and the texturization process should be dominated by the correlation of etching rate and adhesion and desorption rate of additives. We also fabricated solar cells with several texture sizes and evaluated them. The decrease of F.F. with the decrease of texture size was mainly caused by the increase of Rs and this result suggested that we had to optimize the screen printing and firing conditions for the small texture. In addition, there are thick damaged layer on the top and bottom of texture, and these damaged layer cause the deterioration of cell efficiency with texture miniaturization. Reduction of the damage is important to realize high efficiency solar cell using miniaturized texture.
High-efficiency c-Si based interdigitated point contact back heterojunction solar cells
We report on the modeling and performance optimization studies of point contact back heterojunction (BHJ) solar cells. BHJ solar cell technology is a combination of front heterojunction (a-Si:H/c-Si) solar cell technology and interdigitated back junction c-Si solar cell technology. In this work, both emitter (p+-a-Si:H) and back surface field (BSF, n+-a-Si:H) were formed at the rear side as an array of interdigitated points, where their respective contacts formed an interdigitated pattern. The gap between p-type and n-type contact fingers was fixed at 10 µm. The n+-a-Si:H (i.e. BSF) circular diameter was fixed while emitter size was varied, and vice versa. Simulation was also performed with and without passivation layer underneath emitter and BSF. We also investigated the impact of surface texture size on cell efficiency. By varying surface texture size, viz. pyramid height and base width, an efficiency as high as 26.61% was obtained with 761 mV Voc, 41 mA/cm2 Jsc, and 84.5% FF for a small pyramid structure with 2 µm height and 4 µm base width.
Micro-fabrication of crystalline silicon by controlled alkali etching
Abstract AFM is used for sliding and forming silicon dioxide as a cover on the silicon wafer surface (1 0 0) in ambient atmosphere. The silicon dioxide layer (mask) is made through reaction of silicon and oxygen in the atmosphere during the cutting process. Then the silicon wafer samples are etched in alkaline solutions and micro-convex profile (length×width: 5 μm ×5  μm, 10 μm ×10  μm) is formed. As a result of the anisotropic behavior of single crystalline silicon, the etching rates in alkaline solutions depend greatly on the various crystal planes. Effect of etching conditions such as etching temperature and time as well as KOH concentrations of the alkaline solutions on the external appearance, etching rates and height of the micro-protuberances has been studied.