Flexible a-Si Solar Cells with Plastic Film Substrate
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In this paper, first, we briefly describe the concept of PV module for roof named "Solar Roofing" and then present the process technologies for flexible cell with SCAF structure. Next, we present several experimental results in SR Apparatus as well as fabrication result of a large area cell. SOLAR ROOFING The conventional roofing is a waterproof sheet put upon a roof board; roof cover materials such as tiles and slates are fixed on it. The structure of roof developed for the solar roofing is shown in Fig. 1. The solar roofing is a flexible aSi PV sheet having the function of the roofing and tempered glass is used as the roof covering material. Because the installation method of flexible a-Si PV roofing is the same as the conventional roofing sheet, we can apply the solar roofing to any kinds of roofs. An a-Si solar cell with the monolithic series-connected structure is able to generate output voltage as high as that required for direct connection to an inverter. Thus placing flexible a-Si submodules side by side on a waterproof roofing base material and connecting them in parallel, we can cut the solar roofing at anywhere as the conventional roofing sheet can be done. We can use frameless frosted glass and colored glass as roof cover materials from the viewpoint of design and cost.The degradation of plastic films for flexible PV roofing by ultra-violet light will be suppressed since tempered glass cuts off ultra-violet light.
Sectional view
(b) Structure of roof top
(a) Installation of solar roofing
Fig.1 Roof structure with solar roofing.
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"SCAF" STRUCTURE SOLAR CELLS AND PROCESS TECHNOLOGY For fabricating the solar roofing, flexible solar cells with high conversion efficiency and high output voltage are needed. To fabricate such solar cells, we proposed a new solar cell structure and new process technologies for that. In this section, these technologies are described in detail. Stepping Roll Film Deposition Apparatus Figure 2 shows the schematic diagram of Stepping Roll Film Deposition (SR) apparatus propose as a new roll-to-roll deposition system. The basic configuration of the apparatus consists of a common chamber and several film deposition reactors in it. Each reactor has movable heater. During the heater is at lower position, the reactor is completely isolated from the common chamber by O-ring and film. On the other hand, during heater is at upper position, the film substrate can be wound up in the same way as conventional roll-to-roll deposition system. Using this apparatus, various a-Si layers can be deposited simultaneously according to the following sequence: 1) pressing down the heater to isolate the reactor from the common chamber, 2) a-Si deposition, 3) moving up the heater, 4) winding up of one flame. This apparatus has several advantages compared with conventional roll-to-roll deposition system as follows: 1) Interdiffusion of raw material gases among CVD chambers is completely prevented. 2) The reactor is compact because no intricate mechanism like "gas gate' is required.
Film Substrat
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