Theoretical Investigation Of Geminate Recombination At Donor/acceptor Interface Of Organic Photovoltaics

The geminate recombination of donor/acceptor(D/A) interface is important for the monochromatic incident photon-to-electron conversion efficiency and the performance of organic photovoltaics. Therefore, it is significant to study the geminate recombination at interface. The investigations about the geminate recombination of planar/fullerene(pentacene/C60) and dye/fullerene(phthalocyanine(Pc)/C60, copper phthalocyanine(Cu Pc)/C60) and polymer/fullerene(4-poly thiophene(T4)/C60, 6-poly thiophene(T6)/C60) interface are performed in this thesis with the aid of density functional theory and time-dependent density functional theory methods.Structures geometries of donors(Pentacene, Pc, Cu Pc, T4, T6) and acceptor(C60) were optimized and D/A(Pentacene/C60, Pc/C60, Cu Pc/C60, T4/C60, T6/C60) interfaces were built. We calculated and analyzed the engery levels. The Born-Oppenheimer molecular dynamics simulation of interface was performed at 300 K for five interfaces. All of them had been proven to be well equilibrated in the temperature of 300 K because of the equilibration of structure and energy levels. The geometries and charge densities of the five interfaces at different time had been calculated with range-separated time-dependent density functional theory(range-separated TDDFT) method. The phonon modes that affect exciton recombination of D/A interface could be achieved by fourier-transforming the lowest exciton energy level. The recombination of exction from the lowest excited state to the ground state as a function of time had been calculated by the nonadiabatic ab initio molecular dynamics. The geminate recombination rate of Cu Pc/C60 interface was highest. The geminate recombination rate of Pc/C60 interface and T6/C60 interface was lowest. We pointed out that the geminate recombination of Pentacene/C60 could not affect the performance of organic photovoltaics. The copper would greatly accelerate the exciton recombination rate. With the increase of degree of polymerization, the exciton recombination rate would decrease.