Roll-to-Roll Front Contact Patterning by Wire Shading
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Roll-to-Roll Front Contact Patterning by Wire Shading R. Merz, M. B. Schubert, and J. H. Werner Institut für Physikalische Elektronik, Universität Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany ABSTRACT Wire shading during thin film deposition is a promising approach to low-cost, high volume manufacturing of flexible thin film photovoltaic modules. This contribution demonstrates successful patterning of a transparent conducting oxide layer by wire shading during dynamic web coating. Continuous sputter deposition of Al-doped ZnO on a 30 cm wide polymer foil and simultaneous wire shading form 1 cm wide and 300 cm long front contact stripes for thin film photovoltaic modules. Analysing the distribution of lateral shunt resistances after separating the initial 28 stripes into 1323 pieces, yields a patterning success of 97.3 %. Thus the technique seems well suited for flexible modules from organic solar cells. INTRODUCTION A key feature of thin film photovoltaic (PV) module production is the monolithic series connection [2] of the front contact of each solar cell stripe to the rear contact of the adjacent one. The monolithic series connection by laser patterning is well established for thin film PV modules on glass substrates, interconnecting 5 to 15 mm wide cells stripes with total interconnection losses F as low as 3 % < F < 10 % [1,2]. Roll-to-roll manufacturing on flexible foil substrates is another option for low cost, high volume, high throughput mass production of thin film PV modules [3,4]. This roll-to-roll option, however, suffers from remarkably higher interconnection losses due to local heating of the flexible polymer substrates during laser patterning [5]. This contribution introduces the in-situ series connection (ISSC) [6] as an alternative to laser patterning, especially for flexible foil substrates, and presents the first successful patterning of a transparent conducting oxide (TCO) layer by wire shading during dynamic roll-to-roll deposition. The ISSC uses a wire frame which aligns parallel masking wires on the surface of rigid glass or flexible polymer foil substrates, and slightly shifts them between successive thin film depositions. The progress reported here is based on previous ISSC studies that used a static batch processing sequence [7,8]. This study analyses the dynamic in-situ wire shading during web coating of a 30 cm wide polymer foil with highly conductive Al-doped ZnO (ZnO:Al). A 27wire assembly effectively separates 300 cm long ZnO:Al stripes with lateral shunt resistances negligible for thin film PV applications. EXPERIMENT Figure 1 depicts the working principle of the ISSC for aSi based thin film PV modules in superstrate configuration. Paired shading wires locally mask the transparent substrate during deposition of the TCO front contact. After TCO sputtering, a first wire shift #1 enables masking of the front contacts of each cell stripe during the subsequent plasma deposition of the active p-i-n solar cell stack. A final wire shift #2 opens access to the front contacts of the
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