Wavelength-dependent electron injection

The incident monochromatic photon-to-current conversion efficiency (IPCE), also called external quantum efficiency, is defined as the number of electrons generated by light in the external circuit divided by the number of incident photons as a function of excitation wavelength. It is expressed in Equation (7).29 In most cases, the photoaction spectrum overlaps with the absorption spectrum of the sensitizer adsorbed on the semiconductor surface. A high IPCE is a prerequisite for high-power photovoltaic applications, which depends on the sensitizer photon absorption, excited state electron injection, and electron transport to the terminals ... 

The parameter that directly measures how efficiently incident photons are converted to electrons is the IPCE. The wavelength-dependent IPCE term can be expressed as a product of the quantum yield for charge injection ( ), the efficiency of collecting electrons in the external circuit (17), and the fraction of radiant power absorbed by the material or light harvesting efficiency (LHE), as represented by Equation 17.8 ... 

These observations of an excitation wavelength dependence of the charge injection process show that photoinduced interfacial electron transfer from a molecular excited state to a continuum of acceptor levels can take place in competition with the relaxation from upper excited levels. The rather slow growth of the injection... 

DurrantJ. R., Tachibana Y., Mercer 1., Moser J. E., Graetzel M. and King D. R. (1999), The excitation wavelength and solvent dependence of the kinetics of electron injection in Rn(dcbpy)2(NCS)2-sensitized nanocrystalline Ti02 fdms , Z Phys. Chem. 212, 93-98. 

There now exists a large body of experimental data supporting ultrafast electron transfer from MLCTexcited states to the acceptor states of anatase Ti02.112 Most, but not all, of these studies have focused on the famous N3 dye first prepared by Nazeeruddin, cw-Ru(dcb)2(NCS)2.39 In a recent study, an excitation wavelength dependence of the injection process was time resolved.113 Femtosecond injection was attributed to the singlet state and a slower picosecond process from the thermally equilibrated triplet state. 

Moser, J.E. and M. Gratzel (1998). Excitation-wavelength dependence of photo-induced charge injection at the semiconductor-dye interface Evidence for electron transfer from vibrationally hot excited states. Chimia 52, 160-162. 

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