有机太阳能电池内分子间载流子复合动力学研究

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

摘要/Abstract

摘要：

基于载流子复合对有机太阳能电池光伏效率的重要影响，采用扩展的Su-Schrieffer-Heeger紧束缚模型结合非绝热量子动力学方法，对有机太阳能电池内的分子间载流子复合动力学进行理论研究。首先，模拟并揭示了正、负载流子在给/受体界面处的分子间电荷复合动力学过程，发现分子间的载流子复合表现为分数电荷复合并伴随能量的损失。随后，研究体系带阶Δ、电场、热效应和受体分子的聚集对分子间载流子复合动力学的影响。结果表明：体系带阶Δ表现为载流子的复合势垒，带阶越大越利于抑制载流子的复合。电场可以通过诱导正、负电荷的空间离域抑制载流子的复合，特别是，当电场足够强时可以将复合的电荷转移态解离为自由载流子。热效应会引起给/受体材料在位能的随机涨落，降低载流子的复合势垒，进而加剧载流子的复合。受体分子的聚集会诱导电子在受体分子之间的扩展，增大界面处正、负电荷中心的距离，从而抑制载流子的复合。

关键词: 有机太阳能电池, 电荷转移态, 载流子复合, 能量损失

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

中图分类号:

O469

李冲, 王美姣, 葛琳, 曹连振. 有机太阳能电池内分子间载流子复合动力学研究[J]. 计算物理, 2024, 41(2): 182-192.

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.

图/表 8

图1 D/A模型体系

Fig.1 D/A model system

图2 D/A体系初态的能级结构(a) ΔD, n=ΔA, n=0；(b)ΔD, n=ΔD, ΔA, n=ΔA

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

图3 ΔE=0.35 eV时D/A体系内的载流子复合动力学 (a)初态时的净电荷密度分布；(b)净电荷密度分布随时间的演化；(c)各条链上的电荷量随时间的演化；(d)总能量随时间的演化

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

图4 在位能差ΔE对分子间载流子复合的影响 (a)复合电量QR与在位能差ΔE的关系；(b)能量损失Eloss与在位能差ΔE的关系

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

图5 临界电场E=2.0 × 10-3 V·nm-1，ΔE = 0.35 eV时，D/A体系的动力学演化 (a) 电荷密度分布随时间的演化；(b)各条链上的总电荷量随时间的演化

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

图6 热效应对分子间载流子复合的影响(a) ΔE=0.35 eV, T=50 K时，D/A体系的电荷密度分布随时间的演化；(b) 各条链上的总电荷量随时间的演化；(c) ΔE=0.35 eV, 复合电量QR与温度T的关系

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

图7 D/A1/A2模型体系示意图

Fig.7 D/A1/A2 model system

图8 ΔE=0.35eV时D/A1/A2体系内的载流子复合动力学(a) 初态时的净电荷密度分布；(b) 体系净电荷密度随时间的演化；(c)各条链总电荷量随时间的演化；(d)体系总能量随时间的演化

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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