成果報告書詳細
管理番号20140000000705
タイトル*平成25年度中間年報 太陽エネルギー技術研究開発 太陽光発電システム次世代高性能技術の開発 銅ペースト量産化技術と試験・評価方法に関する研究開発
公開日2015/1/31
報告書年度2013 - 2013
委託先名独立行政法人 産業技術総合研究所
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title: Research and Development of Mass Production Technology for Cupper Paste and Evaluation method. (FY 2012-2014) FY 2013 Annual Report

The object of this project is to develop methods to test and evaluate Cu pastes to industrialize Cu paste for low cost crystal silicon solar cell. While some methods to test and evaluate conventionally-used Ag electrode has been already developed, the one for Cu pastes are not fully established. It is necessary to develop the method in order to introduce them into solar cell markets as a PV electrode. The issues to be solved on Cu pastes are as follows: (1) Cu ion can diffuse into crystal silicon so that it interacts with photocarrier centers to recombine. As a result the lifetime of photocarrier decreases and thereby the conversion efficiency decreases; (2) EVA films to encapsulate PV cells can turn the color if Cu ion diffuse into EVA films; (3) Cu ion migration can be one of the sources causing Potential Induced Degradation (PID) because of high internal bias. This year we have been developing a method to detect the lifetime of photocarriers to evaluate whether our developing Cu paste causes diffusion into Si as well as EVA. And also we evaluate a new Cu paste provided by our partner. (1) Diffusion of Cu. In order to measure the lifetime, WCT-120 made by Sinton Instruments was used. Due to the measurement principle, Cu electrode somehow needs to be removed. However, wetting process during the Cu removal causes contamination of Cu, which is dissolved in the etching solution. We found that it is difficult to distinguish between the contamination and genuine Cu diffusion after some experiments. So we put more weight toward IV measurement we have recently developed to assess the diffusion. Double schottky interface was made by depositing two Cu electrodes on a mirror Si surface. Two probes were placed on the two electrode pads to measure the IV characteristic. When Cu electrodes were fabricated by vapor deposition, a limited leakage current was observed. After heating up to 250 degree C for 1h, a significant increase in the leakage current was obtained, followed by some decrease of the current after leaving at room temperature for one day. We found that Cu3Si was generated after the heating treatment by XRD, and reduced to Cu accompanying with SiO2 generation. It explains the leakage current drop after a while since the heating treatment. On the contrary, printed Cu electrodes showed no leakage current even after heating up at 450 degree C. Now we are investigating on the causes. (2) Evaluation of PV performance of Cu electrode on solar cell and its durability. The simplest way to introduce a printed Cu electrode in PV is to use it as a buss bar electrode. We have done it using a conventional PV with a Ag finger electrode and an Al rear electrode. Interestingly, the performance is almost the same as Ag buss bar electrode even after exposure to DHT for 1000hrs, and TC 200 cycle test. It shows printed Cu electrode can be used as a buss bar electrode, which could cost down by 20% estimately, compared to all Ag front electrodes. Now, the performance is being investigated using the printed Cu electrode.
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