Conjugated polymers photoinduced charge transfer

Comparison of the spectral response and of the power efficiency of these first conjugated polymer/fullerene bilayer devices with single layer pure conjugated polymer devices showed that the large potential of the photoinduced charge transfer of a donor-acceptor system was not fully exploited in the bilayers. The devices still suffer from antibatic behavior as well as from a low power conversion efficiency. However, the diode behavior, i.e. the rectification of these devices, was excellent. 

Rice MJ, Gartstein YN (1996) Theory of photoinduced charge transfer in a molecularly doped conjugated polymer. Phys Rev B 53 10764... 

Wu MW, Conwell EM (1998) Theory of photoinduced charge transfer in weakly coupled donor-acceptor conjugated polymers application to an meh-ppv cn-ppv pair. Chem Phys 227 11... 

It is the purpose of this chapter to introduce photoinduced charge transfer phenomena in bulk heterojunction composites, i.e., blends of conjugated polymers and fullerenes. Phenomena found in other organic solar cells such as pristine fullerene cells [11,12], dye sensitised liquid electrolyte [13] or solid state polymer electrolyte cells [14], pure dye cells [15,16] or small molecule cells [17], mostly based on heterojunctions between phthalocyanines and perylenes [18] or other bilayer systems will not be discussed here, but in the corresponding chapters of this book. 

For photovoltaic cells made with pure conjugated polymers, energy conversion efficiencies are typically 10-3-10-1%, too low to be used in practical applications [18,59]. Photoinduced charge transfer across a donor/acceptor (D/A)... 

This photoinduced charge transfer between conjugated polymers as donor and fullerenes as acceptor takes place within less than 50 fs [54]. Since all competing processes like photoluminescence ( ns) and back transfer and thus recombination of the charge ( xs) [8-10] take place on a much larger timescale, the charge separation process is highly efficient and metastable. These possible pathways for the decay of the system after excitation are displayed in Fig. 5 for comparison. 

Pientka M, Dyakonov V, Meissner D, Rogach A, Talapin D, Weller H, Lutsen L, Vanderzande D (2004) Photoinduced charge transfer in composites of conjugated polymers and semiconductor nanocrystals. Nanotechnology 15 163... 

S. J. Chen, A New Conjugated Polymer with Donor-Acceptor Architectures Based on Alternating 1,4-Divinyl-2,5-Dioctyloxybenzene and 5,8-(2,3-Dipyridyl)-Quinoxaline Synthesis, Characterization, and Photoinduced Charge Transfer. Express Polym. Lett. 2012,6,454-464. 

Lin Y-T, Zeng T-W, Lai W-Z, Chen C-W, Lin Y-Y, Chang Y-S, Su W-F (2006) Efficient photoinduced charge transfer in Ti02 nanorod/conjugated polymer hybrid materials. Nanotechnology 17(23) 5781—5785... 

TCNQ and TCAQ acceptors exhibit a significantly lower rate of photoinduced electron transfer, despite the fact that they are better acceptors than TCTQ, 5,14-TCPQ and Ceo- A qualitative interpretation for such behaviour was predicted from the Marcus theory for electron transfer and referred to as the inverted region [139]. On the other hand, the efficient photoinduced charge transfer of MEH-PPV in combination with acceptors TCTQ, diMeO-TCTQ, 5,14-TCPQ and C6o, compared with the lack of activity for 1,4-benzoqui-nones with a similar reduction potential value, indicates that the reduction potential is not the only parameter that affects the electron-transfer rate. Nevertheless, phase segregation and the solubility of the acceptors within the conjugated polymer might make difficult the interpretation of the observed results [135]. 

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