Laser Scribing of W-textured ZnO Substrates Using Green Laser
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Laser Scribing of W-textured ZnO Substrates Using Green Laser
Ryousuke Ishikawa1, Hidetoshi Wada1, Yasuyoshi Kurokawa1, Porponth Sichanugrist1 and Makoto Konagai1, 2 1 Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan 2 Photovoltaics Research Center (PVREC), Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan ABSTRACT Thin-film silicon solar cells have been attracted a lot of intention as low-cost solar cells. One of the most important technologies for improving their performances is light trapping. We have demonstrated the high potential of double-textured zinc oxide (ZnO) thin films used as front transparent conductive oxide (TCO) films due to further enhancement of their lighttrapping effects. Although the laser scribing method has already been well established for lowcost thin-film silicon solar cell module manufacturing, laser scribing technique on doubletextured ZnO is new and still a challenging issue. In this study, we firstly demonstrated the availability of laser scribing for amorphous silicon (a-Si) solar cells fabricated on doubletextured ZnO substrates. It is general to utilize lasers with wavelength of 1.06 Pm and 532 nm for scribing of TCO and silicon layer, respectively. Here we attempted to scribe both of TCO and silicon layers using a 532 nm wavelength laser (green laser) for process simplifying. INTRODUCTION Thin-film silicon solar cells are low-cost technology with potential for further cost reduction and suitable for large-scale implementation [1, 2]. Light trapping is an emerging issue for improving the performance of thin-film silicon solar cells. Especially the front electrodes in the superstrate p-i-n type thin-film silicon solar cells show a huge impact on the conversion efficiency [3, 4]. To improve the light trapping effect, particularly in the long-wavelength region, we have demonstrated the high potential of double-textured ZnO thin films with very high haze values [5, 6]. The haze value of double-textured ZnO film is up to 92 % at wavelength of 800 nm without any drastic change of electrical properties. The efficiency of p-i-n type a-Si solar cells fabricated on double-textured ZnO was improved from 10.33 % to 10.89 % [7], compared with that of solar cells on conventional ZnO. This improvement was mainly attributed to the enhancing of short-circuit current (Jsc) by the favour of light trapping. In view of large-area industrial manufacturing of thin-film silicon solar cells, the application of the integrated series connection technique based on the laser scribing is an essential process. In the case of a-Si based solar cells, the laser scribing method has already been well-established in the fabrication of large size modules [8-10]. The pattern 1 (P1) scribing thus forms isolate the front contact between the cells. The absorber layer of a-Si or a-Si / microcrystalline silicon (Pc-Si) for a single or tandem cells are then deposited. This is followed by the pattern 2 (P2) laser process which forms
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