Controllable charge transfer in quantum dot (QD)/dye composites working as light absorbers is crucial for solar energy conversion. Conventionally, the photoinduced charge transfer rate is well described within the Marcus theory that predicts it being proportional to the thermodynamic free energy. However, this proportional relation is broken due to the strong electronic coupling, according to recent experimental studies on the CdSe QD functionalized by Co(III) complex. Inspired by these results, we apply density functional theory (DFT) to study in detail the effect of electronic coupling on charge transfer rates in Cd33Se33 QD functionalized by N719 dye (Di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2’-bipyridyl-4,4’-dicarboxylato)ruthenium(II)). Our results show that the electronic coupling vector V is altered with the orientation of N719 dye on the surface of Cd33Se33. The highest occupied molecular orbital (HOMO) in the Cd33Se33/N719 composite is dictated by the electronic states in N719 dye that are localized on the carboxylate group or the thiocyanate group or both, depending on the surface attachment. For excited state properties, the linear-response time-dependent density functional theory (TDDFT) shows that the orientation of the dye on the QD’s surface also changes the electronic coupling, which either promotes or inhibits an instant charge transfer between the QD and the dye in Franck-Condon limit. Time-domain nonadiabatic molecular dynamics is carried out to obtain the non-adiabatic electron and hole transfer rates across the heterojunction interfaces in Cd33Se33/N719 structures, where the electronic coupling vector V is perturbed by vibrational motion along the non-adiabatic trajectory. Overall, our results rationalize a controllable charge transfer rate through manipulating the attachment of N719 dye, which can assist a better design of nano-composites with enhanced properties for photovoltaic devices.

Effect of electronic couplings on charge transfer rates in Cd33Se33 quantum dots functionalized by Ru(II) complexes

251st National Meeting (2016)

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