Abstract
We report on excitation dynamics in pristine and bulk heterojunction films of the low bandgap silicon-bridged dithiophene copolymer poly[(4,4'-bis(2-ethylhexyl) dithieno[3,2-b:2', 3'-d]silole)-2, 6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5'-diyl] with methanofullerene derivatives. The combination of ultrafast transient transmission and photoluminescence allows us to probe the relaxation of both exciton and polaron states in a relatively wide spectral and temporal range. Measurements reveal that the majority of excitations undergo ultrashort non-radiative relaxation while a small fraction of the photoexcited species decays slowly within hundreds of ps. In the blend films, significantly longer decays are observed suggesting the presence of long lived holes and/or charged-transfer type of excitons. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3703601]