유기 박막 태양전지 버퍼층을 위한 정전기력 분무기반의 증착 기술

Abstract

The world energy consumption is ever increasing but the production is not able to meet this growing demand and acute energy shortage is expected in the near future. The world nations are working on developing renewable energy sources to meet this growing energy demand. Most countries are showing interest in solar energy because of its abundance. solar cell technology is divided into inorganic solar cell technique representing crystalline silicon and organic thin film solar cell based on organic matter. Now 90% of solar cell produced are inorganic crystalline silicon solar cell which occupy most of the industry. But crystalline silicon solar cell technique is hard to get to economic feasibility because of high material price recently. Therefor, the organic thin film solar cell which is more affordable compared to other technologies is considered as a alternative instead of crystalline silicon solar cell in spite of the technique of the stability and high conversion efficiency of crystalline silicon solar cell. Earlier Organic thin-film solar cells did not attract many researchers because of its low efficiency. However recent developments in Organic solar cell research and its relatively inexpensive characteristics with the usage of solution processed organic materials make it an ideal candidate as an energy source. Others advantages include the wide range availability of substrates, large area productivity as well as the few hundred um thickness of the entire device and flexible substrates insure the use of organic photovoltaics in innovative uses, such as mobile communication. Since the organic thin-film solar energy conversion efficiency needs improvement, a buffer layer is introduced between the electrodes and the active layer. The enhanced injection current and work function of the organic thin-film solar cell improves the energy conversion efficiency and many researches and studies are in progress on this aspect of organic solar cells. Typical buffer layer material for organic solar cells is a polymer PEDOT: PSS (poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate)) and is usually used as a film between electrodes and active layer. The conventional deposition methods include solution lift-off process, etching and screen printing. Another very popular method for the deposition of PEDOT:PSS is spin coating method.[5] However, the etching process contains different steps like coating, exposure, developing, and etching resist removal process which are complex processes and during these processes, release of various pollutants can cause environmental pollution. As far as other processes are concerned, screen printing and spin coating processes, when deployed for printing 10 um or less, the layer uniformity is not very high and also a high viscosity material can not be processed. Also an inherited disadvantage of all these process is that they can not be used for bulk manufacturing processes like Roll-to- Roll etc and hence energy efficiency and production efficiency are largely compromised with these processes. Therefore, to increase the energy efficiency and for efficient manufacturing of organic thin-film solar cells, more research is required for the efficient and pollution-free formation of the buffer layer of the thin film organic solar cells. Deposition through electrostatic deposition carries many advantages for the manufacture of printed electronics. The main advantage is the simplicity of the process and very high material usage. There are effectively no pollutant emissions and the process is inherently an environment friendly process. The process is low cost and can be very easily integrated to any bulk manufacturing process for mass production of the devices. In addition, the process is capable of producing thin layers of hundreds of nm and solution with viscosity as high as 100cps can be processed with this deposition technique. In this thesis, the electrospray deposition of PEDOT:PSS has been discussed to improve the organic thin-film solar cell production efficiency. The process development, technology, research, and comparison of conventional PEDOT: PSS deposition processes with the electrostatic spray-based coating process are discussed in detail. The PEDOT: PSS electrostatic spray deposition has been discussed in the light of nozzle development, the spray system development, and complete process' description with experimental results. Different parameters of the deposited PEDOT: PSS thin films have been characterized, for example the thin-film uniformity, film conductivity and device efficiency.