Nonradiative charge trapping processes

Fig. 13 Photo-induced processes occurring during photovoltaic energy conversion at the surface of the nanocrystalline titania films, 1 sensitizer (S) excitation by light, 2 radiative and nonradiative deactivation of the sensitizer, 3 electron injection in the conduction band followed by electron trapping and diffusion to the particle surface, 4 recapture of the conduction band electron by the oxidized sensitizer (S+), 5 recombination of the conduction band electrons with the oxidized form of the redox couple regenerating the sensitizer and transporting the positive charge to the counterelectrode. Grey spheres, titania nanoparticles, red dots, sensitizer, green and blue dots oxidized and reduced form of the redox couple. See Color Plates...

In conjugated polymers a similar nonradiative quenching process as observed for molecular crystals [2] happens if a SE encounters a trapped or free polaron—acting as a charged defect—during the migration process ... 

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