Study on the Intermolecular Carrier Recombination Dynamics in Organic Solar Cells

doi:10.19596/j.cnki.1001-246x.8704

Abstract

Abstract:

Based on the important effect of carrier recombination on the photovoltaic efficiency of organic solar cells, the intermolecular carrier recombination dynamics in organic solar cells is studied theoretically by using an extended Su-Schrieffer-Heeger tight binding model combined with the non-adiabatic quantum dynamical method in this article. Firstly, intermolecular charge recombination dynamics of the positive and negative carriers at the donor/acceptor interface is simulated and revealed, and it is found that the intermolecular carrier recombination exhibits fractional charge recombination along with energy loss. Subsequently, influence of the system energy offset Δ, electric field, thermal effect and aggregation of acceptor molecules on intermolecular carrier recombination dynamics is studied. The results show that the system energy offset Δ exhibits the carrier recombination barrier, and the larger the energy offset Δ, the more favorable it is to suppress the recombination of carriers. The electric field can inhibit the recombination of carriers by inducing spatial delocalization of positive and negative charges. Especially, as the electric field is strong enough, it can dissociate the recombined charge transfer state into free carriers. Thermal effects can cause random fluctuations of the potential energy of the donor/acceptor material, which can reduce the recombination barrier of carriers, and further to aggravate the carrier recombination. The aggregation of acceptor molecules will induce the expansion of electrons between acceptor molecules, increasing the distance between positive and negative charge centers at the interface, thereby inhibiting the recombination of carriers.

Key words: organic solar cells, charge-transfer state, carrier recombination, energy loss

CLC Number:

O469

Chong LI, Meijiao WANG, Lin GE, Lianzhen CAO. Study on the Intermolecular Carrier Recombination Dynamics in Organic Solar Cells[J]. Chinese Journal of Computational Physics, 2024, 41(2): 182-192.

Figures/Tables 8

Fig.1 D/A model system

Fig.2 Energy level structure of the initial state of the D/A system (a) ΔD, n=ΔA, n=0;(b)ΔD, n=ΔD, ΔA, n=ΔA

Fig.3 Charge carrier recombination dynamics in the D/A system with ΔE = 0.35 eV (a) net charge density distribution in the initial state; (b) evolution of net charge density distribution with time; (c) evolution of total charges on separated chain with time; (d) evolution of total energy with time

Fig.4 Effect of the on-site energy difference ΔE on intermolecular carrier recombination (a) relationship between charge-recombination quantities and the on-site energy differences ΔE; (b) relationship between the energy loss Eloss and the on-site energy differences ΔE

Fig.5 Dynamical evolution of D/A system with critical electric field E=2.0 × 10-3 V·nm-1 and ΔE= 0.35 eV (a) evolution of net charge density distribution with time; (b) evolution of total charges on separated chains with time

Fig.6 Effect of thermal effect on intermolecular carrier recombination (a) evolution of net charge density distribution of D/A system with time for ΔE = 0.35 eV and T = 50 K; (b) evolution of the total charges on separated chains with time; (c) relationship between charge-recombination quantities and the temperature T as ΔE=0.35 eV

Fig.7 D/A1/A2 model system

Fig.8 Charge carrier recombination dynamics in D/A1/A2 system for ΔE = 0.35 eV (a) net charge density distribution in the initial state; (b) evolution of net charge density distribution with time; (c) evolution of total charges on separated chain with time; (d) evolution of total energy with time

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