Study Of Parylene Coating And Its Application On Low Working Temperature Crystalline Silicon PV Modules

The output power of crystalline silicon PV modules has an obvious temperaturecharacteristic. With the increasing of its working temperature, the maximum output power (Pm)will be decreased linearly which shows a characteristic of negative temperature coefficient at-0.5%/℃. Global photovoltaic power generation system consists of thousands of single PVmodules, increasing working temperature will lead to a huge loss of solar energy. In thisdissertation, we used paralene ultra-thin insulating coating which was coated onto solar cells andbacksheets to get a great insulating property. Meanwhile, we replaced polymer backsheets withaluminium backsheets to improve heat dissipation performance.Firstly, we researched Gorham CVD method to deposit parylene-C films onto solar cells.We used FTIR to analyze chemical structures, and used SEM to observe the morphology. Wefound that parylene-C films showed an epitaxial growth along the original morphology of the backelectrode of the solar cell, and it had a compact coating performance. DSC and TGA tested thethermal performance of the parylene-C film. Its melting range was260~290℃and parylene-Cstarted to decompose at about249℃. Excellent thermal performance of parylene-C demonstratedthat its property would not be effected after PV module lamination.Secondly, we researched on depositing parylene-N films which had a comparative DCbreakdown strength by plasma enhanced chemical vapor deposition (PECVD). By changing threefactors of r.f. power, para-xylene flow rate and deposition time, we studied on the performance ofprepared parylene-N films by PECVD. We reached three conclusions:1. Under a fixed gas flowrate and deposition time, with the increasing of r.f. power, the deposition rate will raise; but whensharply increasing the input energy, high input energy would lead to open the aromatic rings sothat made monomer harder to polymerize. And, with increasing power, the breakdown strengthwill increase; when further increasing the power to100W or above, the breakdown strength willdecrease. With higher power, the film showed a hydrophobicity.2. Under a fixed r.f. power and deposition time, with the increasing of PX flow rate, it will increase the collisionprobability among radical spices which improve the polymerization and deposition rate ofparylene films. When increasing the para-xylene flow rate, the power imposed on monomers perunit volume will decrease, which will reduce the degree of crosslinking and compactness so thatits breakdown strength will reduce. With lower PX flow rate, the film showed a hydrophobicity.3.Under a fixed r.f. power and gas flow rate, film thickness has a linear relation with deposition time.With the increased deposition time, the plasma will have a further influence on polymerized filmsto crosslink and this will improve compactness so that breakdown strength will rise a little.Deposition time showed no influence on WCA. PECVD method replaced pyrolysis with plasma,and it integrated surface cleaning, modification and deposition into one chamber. Parylene filmsprepared by PECVD had a comparative DC breakdown strength and had a much lower costcompared by CVD methodFinally, we developed a new type of low working temperature PV module. The first PVmodule sample consisted of parylene-C coated solar cells and a parylene-C CVD coatedaluminum panel. The second PV module sample has parylene-C coated solar cells but a barealuminum panel. We conducted indoor tests and outdoor tests. The low working temperature PVmodules meets the requirements of peel test and insulation test. From three parts of steady solarexposure test, infrared thermal imaging test and real-time temperature monitoring test, we proveda better heat dissipation performance of our low working temperature PV modules than commonPV modules. At a solar irradiance less than300W/m2, the temperature of Al-backsheet moduleswould be about0~1.0℃lower and0~0.5%power loss would be reduced. If solar irradianceclimbed up to more than800W/m2, it was supposed to be0.5~1.4%power loss that would bereduced. As mentioned above, a new type of low working temperature PV module via acombination of parylene ultra-thin insulating coating by CVD and aluminum backsheet had bothexcellent insulating property and heat dissipation performance.