Reliability Studies of Mo Back-Contact with Embedded Silver Nanowires for Flexible CuInGaSe2 Solar Cells Applications

• Main Authors: Ming-ChenHung, 洪銘辰
• Other Authors: Dung-Ching Perng
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/70883670515688026890

碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 101 === In this thesis, we investigated the strain-induced reliability of back-contact for electrode deposited on polyimide (PI) substrate for flexible CIGS solar cells applications, and we integrated the electrode with silver nanowires (NWs) to enhance the flexibility of the back-contact electrode. The thesis content can be divided into three subjects. The first one is the investigation of cracks induced by the internal strain resulting from the fabrication process and the method we used to fix cracks of the conventional Mo back-contact electrode. For the second subject, the reliability of pure Mo and Al- or Ag-added Mo structures were evaluated by a home-made bending tester. For the last subject, silver NWs-embedded contacting layers as an electrode were evaluated. It demonstrated superior performance with minimal resistivity evolution before and after the bending tests and more flexibility than the conventional Mo electrodes. First, various efforts to reduce process-induced strain, such as lowering the annealing ramping rate, depositing an additional back-side Mo film, and adding an Mo annealing pretreatment, were investigated. The annealing ramping rate was adjusted from 25 to 5⁰C/min to minimize the thermal stress of Mo film but had no success in fixing the cracks. Neither could the additional back-side Mo film fix the cracks, but only served to reduce the sample curving after the selenization process. In one instance, crack of Mo electrode was fixed by a one hour 390⁰C annealing pretreatment, but the reproducibility was very low. The annealing pretreatment could improve the Mo film quality and partially alleviate the process-induced strain. For the second subject, we fabricated Al- and Ag-added Mo structures, including MoAl, MoAg alloys and Al/Mo, Ag/Mo bi-layer structures, as alternative contacting layers. The annealing pretreatment was applied to these structures for further improvement. A bending test was designed to study the flexibility of these various structures. For the as-deposited films, none of the Al- and Ag-added Mo structures exhibited a better performance in the bending test than that of the conventional Mo, which could sustain 0.16% tensile strain and 0.28% compressive strain without obvious resistance increment. The annealing pretreatment did boost the sustainability of tensile strain up to 0.42% for Mo, MoAl and MoAg structures, but the pretreatment on pure Mo is more effective than those impurity-added Mo structures. In the final subject, the silver NWs-embedded Mo layers, Mo/Ag NWs/Mo (MAM) and Ag NWs/Mo (AM) structures, with or without annealing were studied. CIGS film was formed on these structures for further investigation. For the as-deposited structures, macroscopic cracks occurred on the CIGS films and the electrode layers after the selenization process. Their resistances were increased to 100 ohm from tens ohm under 1.68% highly tensile or compressive strain. For the annealed structures, crack-free electrodes with low resistance (3.12 Ω, 1.04 Ω/□) were observed. They demonstrated more flexible (resistance kept below 5.6Ω and 3.2 Ω after 5-cycle 0.84% tensile and compressive bending respectively) and the superior performance of the MAM electrode is reproducible.