Reduced Charge Transfer Exciton Recombination in Organic Semiconductor Heterojunctions by Molecular Doping

Abstract

We investigate the effect of molecular doping on the recombination of electrons and holes localized at conjugated-polymer–fullerene interfaces. We demonstrate that a low concentration of $p$-type dopant molecules ($<4\%$ weight) reduces the interfacial recombination via charge transfer excitons and results in a favored formation of separated carriers. This is observed by the ultrafast quenching of photoluminescence from charge transfer excitons and the increase in photoinduced polaron density by $\sim 70\%$. The results are consistent with a reduced formation of emissive charge transfer excitons, induced by state filling of tail states. DOI: http://dx.doi.org/10.1103/PhysRevLett.107.127402 © 2011 American Physical Society