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Organic photovoltaic devices (OPVs) are fabricated from thin films of organic semiconductors, such as polymers and small-molecule compounds, and are typically on the order of 100 nm thick. Because polymer based OPVs can be made using a coating process such as spin coating or inkjet printing, they are an attractive option for inexpensively covering large areas as well as flexible plastic surfaces. A promising low cost alternative to conventional solar cells made of crystalline silicon, there is a large amount of research being dedicated throughout industry and academia towards developing OPVs and increasing their power conversion efficiency. == Single wall carbon nanotubes as light harvesting media == Single wall carbon nanotubes possess a wide range of direct bandgaps matching the solar spectrum, strong photoabsorption, from infrared to ultraviolet, and high carrier mobility and reduced carrier transport scattering, which make themselves ideal photovoltaic material. Photovoltaic effect can be achieved in ideal single wall carbon nanotube (SWNT) diodes. Individual SWNTs can form ideal p-n junction diodes. An ideal behavior is the theoretical limit of performance for any diode, a highly sought after goal in all electronic materials development. Under illumination, SWNT diodes show significant power conversion efficiencies owing to enhanced properties of an ideal diode. Recently, SWNTs were directly configured as energy conversion materials to fabricate thin-film solar cells, with nanotubes serving as both photogeneration sites and a charge carriers collecting/transport layer. The solar cells consist of a semitransparent thin film of nanotubes conformally coated on a n-type crystalline silicon substrate to create high-density p-n heterojunctions between nanotubes and n-Si to favor charge separation and extract electrons (through n-Si) and holes (through nanotubes). Initial tests have shown a power conversion efficiency of >1%, proving that CNTs-on-Si is a potentially suitable configuration for making solar cells. For the first time, Zhongrui Li demonstrated that SOCl2 treatment of SWNT boosts the power conversion efficiency of SWNT/n-Si heterojunction solar cells by more than 60%. Later on the acid doping approach is widely adopted in the later published CNT/Si works. Even higher efficiency can be achieved if acid liquid is kept inside the void space of nanotube network. Acid infiltration of nanotube networks significantly boosts the cell efficiency to 13.8%,as reported by Yi Jia, by reducing the internal resistance that improves fill factor, and by forming photoelectrochemical units that enhance charge separation and transport. The wet acid induced problems can be avoided by using aligned CNT film. In aligned CNT film, the transport distance is shortened, and the exciton quenching rate is also reduced. Additionally aligned nanotube film has much smaller void space, and better contact with substrate. So, plus strong acid doping, using aligned single wall carbon nanotube film can further improve power conversion efficiency (a record-high power-conversion-efficiency of >11% was achieved by Yeonwoong Jung). Zhongrui Li also made the first n-SWNT/p-Si photovoltaic device by tuning SWNTs from p-type to n-type through polyethylene imine functionalization. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carbon nanotubes in photovoltaics」の詳細全文を読む スポンサード リンク
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