Shape-Controllable Surface Texturization for Crystalline Silicon Solar Cells
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Shape-Controllable Surface Texturization for Crystalline Silicon Solar Cells Jong-San Im, Jin-Wan Jeon, and Koeng Su Lim Electrical Engineering & Computer Science, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-dong, Yuseong-gu, Daejon, 305-701, Korea, Republic of ABSTRACT This paper describes a new method to make surface textures for photovoltaic application. Using this method, we can make textures having various shapes. The first step is to make photo-resist (PR) molds using the polymer dispersed liquid crystal (PDLC) film. The second step is to transfer the PR molds to silicon by inductively coupled plasma etching process. The final step is a solar cell fabrication process. The structure of the solar cell is simple Al Grid/c-Si/Al back contact. The solar cells show the increase of the short circuit current (Jsc) comparing to the planar cells. By this texturing method, we can get solar cells having various textures which we want to make. INTRODUCTION Reduction of surface reflectance is very important for solar cells to improve cell performances since it increases short circuit currents and that means an efficiency improvement. In case of the planar silicon surface, it reflects approximately 30% of incident light. To reduce light reflection, surface textures were made on the front surface. Surface textures increase the light absorption by multiple reflections and the longer average path length of incident light within solar cells. So the light absorption of the textured surface is higher than that of the planar surface. To make surface textures, many fabrication processes were performed. Wet-chemical alkaline anisotropic etching was used to make inverted pyramid textures on the top surface [1]. Reactive ion etching was also applied to make surface textures [2]. However, these methods can make only a restricted shape. Using these, we can’t make various texture profiles. For example, wet-chemical alkaline anisotropic etching can make just inverted pyramids having a slope angle of 24.7°. But, if we can make the various textures, we can find the optimized shape for the photovoltaic application. That’s the reason why we investigated the way to make surface textures having controlled shapes to see the effect of the shape of textures. In this work, we used a new surface texturing method using the polymer dispersed liquid crystal (PDLC) film. The PDLC film is now investigated to make 3D structures easily [3]. Using the PDLC, We made various textures by applying voltages and changing applied UV-dose. The various shapes of Photo-resist (PR) for texturing are presented. Finally, crystalline solar cells using these textures were made to see the effects of shape variations. EXPERIMENT We propose a new surface texturing method using the PDLC film. Light scattering rate through the PDLC film is controlled by varying the applied voltage across the PDLC film. At
zero applied voltage, the PDLC film scatters incident light to every direction, and as the applied voltage is higher, the scatter
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