Photogeneration fullerenes

Magnetic field effects on the reaction kinetics or yields of photochemical reactions in the condensed phase have been studied [20-23]. They have proved powerful for verifying the mechanism of photochemical reactions including triplet states. Previously, we obtained photogenerated triplet biradicals of donor-acceptor linked compounds, and found that the lifetimes of the biradicals were remarkably extended in the presence of magnetic fields up to 1T [24]. It has been reported that Cgo and its derivatives form optically transparent microscopic clusters in mixed solvents [25,26]. The clustering behavior of fullerene (C o) is mainly associated with the strong three-dimensional hydrophobic interactions between the C o units. Photoinduced... 

Muller JG, Lupton JM, Feldmann J, Lemmer U, Scharber MC, Sariciftci NS, Brabec CJ, Scherf U (2005) Ultrafast dynamics of charge carrier photogeneration and geminate recombination in conjugated polymer fullerene solar cells. Phys Rev B 72 195208... 

In order to learn about the true quantum efficiency of photogeneration one therefore has to study the photoinduced charge generation mechanism at faster time scales. Pump probe spectroscopy utilising a few optical-cycle laser pulses (5-6 fs) in the visible spectral range with broadband frequency conversion techniques [89] now makes it possible to study extremely fast optically-initiated events with unprecedented time resolution. Such a setup was used to time-resolve the kinetics of the charge transfer process from a polymer chain to a fullerene moiety in thin films of poly[2-methoxy, 5-(3, 7 -dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV) and [6,6]-phenyl C6i butyric acid methyl ester (PCBM). Solutions prepared from 1 wt% solutions of toluene on thin quartz substrates were studied. 

Fluorene- or fullerene-thiophene blends have been developed for enhanced photogeneration <2007CPC1497>, and use in light emitting diodes <2007MM6164>, and copolymers of oxadiazoles and thiophenes <2007MI236> have been used for non-linear optical applications. 

T.M. Clarke, A.M. Ballantyne, J. Nelson, D.D.C. Bradley, and J.R. Durrant, Free energy control of charge photogeneration in polythiophene/fullerene solar cells The influence of thermal annealing on P3HT/PCBM blends, Adv. Fund Mater., 18, 4029 035 (2008). 

Charge Carrier Photogeneration and Transport in Polymer-Fullerene Bulk-Heterojunction Solar Cells, Chapter 15 in W. Brrit-ting (ed.). Physics of Organic Semiconductors, Wiley-VCH, Weinheim (2005). 

Fig. 7.3 Electronic state diagram and (in horizontal perspective) schematic charge photogeneration and transport in a polymer fullerene photovoltaic cell. The migration of the exciton to the BHJ generates a CT exciton that may dissociate into free charge carriers, recombine to the ground state or intersystem cross to the triplet exciton (not shown in this figure). Chaige separation is believed to occur from a hot exciton, in competition with its thermalisation. The built-in electric field created by the electrode work function differential drives the electrons to the cathode and the holes to the anode...

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