Quantum Dynamics Study Of Photoinduced Excited State Energy Transfer In Organic Solar Cells

Organic solar cells?OSCs?are promising alternatives for inorganic photovoltaic devices due to their advantages such as flexibility,simple processing process,low cost,etc.The solar energy conversion of OSCs begins with photoabsorption,by which the excitonic states of donor materials are generated.The exciton transfer from one molecule to the other is just the excited energy transfer?EET?process in dimer.In this paper,we investigated the EET dynamics process in the DTDCTB dimer embedded in the environment by using quantum dynamics.Firstly,we want to investigate the EET dynamics process in the DTDCTB dimer included in the environment by using multilayer multiconfiguration time-dependent Hartree?ML-MCTDH?approach.This DTDCTB dimer system has two different stacking along OA axis in the DTDCTB crystal.The Hamiltonian of this system used a two-state model which consists of the first and the second local excited states.We built the diabatic Hamiltonian by using projection method.And we used ONIOM method to dispose constructing the normal mode.As costing a long time of running the full dimensional quantum dynamics,we deal with the full dimensional modes by using spectral density method.The modes is re-discretized for less number.Then we simulated the EET dynamics using different number of re-discretized modes and different Lorentzian width with ML-MCTDH.The results show the existence of an ultrafast EET process in this system.We can use less re-discretized modes to characterize the whole EET dynamics process.Using different Lorentzian width has small effect on the dynamics process.Furthermore,diabatic Hamiltonian model of the DTDCTB crystal will be constructed based on the reduced model of dimer systems and corresponding quantum dynamics will be carried out in the future work.Secondly,we investigated the TSH dynamics at TDDFT level in the CH₂NH₂⁺ molecular system from high-lying states by using JADE package.Through the TSH method,the dynamics with the starting on the singlet excited states?S₃/S₄/S₅?are simulated.The analysis of dynamic results shows that the dissociations of CN and CH/NH hardly occur at the same time.Along with becoming higher of excited state,the increasing of dissociations' number of the CH/NH induces the decrease of system's energy and fewer dissociations of CN bond.And the torsional motions are not dominant in the TSH dynamics from the high-lying excited states.