Polythiophene photovoltaic devices

Several attempts to use otganic polymeric semiconductors as the active component in photovoltaic devices have been reported during the last two decades. Interest in the photovoltaic properties of conjugated polymers like polyacelylcne, various derivatives of polythiophenes and poly(para-phenylene vinylene)s arose from... 

Polythiophenes (PTs)/CNTs composites have emerged as an intriguing system for use as photovoltaic devices and field effect transistors [57]. Swager and Bao independently reported methods for the assembling of PTs/CNTs systems and showed their great potential as transparent conductive films [58]. Another interesting application arises from the possibility to functionalize the polythiophene backbone for applications as chemical sensors [134]. 

In other EFM studies,158 part of the sample was electrochemically oxidized by partially immersing in electrolyte and applying a positive potential. The EFM image clearly showed a distinction between the immersed (oxidized) and nonimmersed (less oxidized) parts of the sample in terms of relative work function. Similar shifts in work function had also been observed for polythiophenes when exposed in situ to ultraviolet (UV) radiation during EFM imaging.160 An increase in the work function upon UV exposure is due to the formation of electron-hole pairs that produce photocurrent in photovoltaic devices. Thus, the EFM provides fundamental insights into the processes involved in many of the applications for CEPs. 

Currently the best-performing heterojunction photovoltaic devices are made from blends of polythiophenes and PCBM [6,106]. Here, the charge-transfer states are stable with respect to triplet excitons, which comes at the cost of modest open-circuit voltages of 0.6V. Recent experimental evidence suggests that the high performance of PCBM polymer solar cells could also be attributed to the kinetic advantage in charge-transfer state separation that these cells have over those made from amorphous polymers. It is... 

More recently, polythiophenes, some of which were substituted with porphyrin moieties as light harvesters, had been investigated for their performances in photovoltaic devices. In an original work, Shinkai et al. succeeded in the electropolymerization of a Ce(III) triple decker porphyrin complex bearing bithienyl substituents at an ITO electrode surface. ... 

Due to their conducting properties, polythiophenes can only be used in photovoltaic devices in their reduced state. The reduction must take place electrochem-ically before vapor deposition of the top electrode. Different layer structures and combinations of PT with PPPV or Ceo were studied [275,276]. Al/Ceo-modified PT/ITO devices exhibit a conversion efl ciency of 15% with zero bias and 60% with a bias of 2 V (for A = 500 nm, 1.5 mWcm ). 

Too CO, Wallace GG, Burrell AK, Collis GE, Officta- DL, Boge EW, Btodie SG, Evans E (2001) Photovoltaic devices based on polythiophenes and substituted polythiophenes. J Synth Met 123 53-60... 

Oligothiophenes with well defined structures have recently received a great deal of attentions not only as a model eompoimds for conducting polymers, but also as anew class of functional r-electron systems [153], Since the initial discovery of organic compounds showing metallic conductivity, for which 2000 Nobel prize in chemistry was awarded [154-156], oligo- and polythiophenes have attracted much attention as advanced molecules with practical use in electronic devices [157-160] and their potential application in field-effect transistors [161], photovoltaic devices [162] and organic electroluminescent devices [163],... 

Whereas in solution the photoluminescence efficiency (Of) of poly(3-alkylthiophenes) (PATs) is 3(Mf)%, it drastically drops to 1-4% and lower in the solid state due to the increased contribution of nonradiative decay via interchain interactions and ISC caused by the heavy-atom effect of sulfur (97MM4608). Optoelectronic devices of this type of compounds have been studied (98SCI(280)1741 06SM(156)1241). Fibers of poly(3-hex-ylthiophene) for photovoltaic applications have been described (07MI1377). Poly(3-octylthiophene) showed a TTA band at 800 nm (96JPC15309). The photophysical properties of some alkyl and aryl polythiophenes have been studied (03JCP(118)1550). The absorption maximum of poly(3-octylthiophene) is at 438 nm, while the fluorescence was... 

A great deal of work has been done to characterize the structure of films cast from chemically prepared polythiophenes.96 Most of this work has been conducted on undoped PTh s because of their importance in electronic devices, such as thin-film transistors and photovoltaics. Depending on composition and processing conditions, the crystallinity can be as high as 30% in polythiophenes.97 A layered structure is usually formed in PTh crystals between extended chains held together by ir-slacking, with additional structural order introduced by alkyl side-chain interactions in functionalized PTh s.98 Chemically synthesized PTh powders exhibit a... 

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