A new perspective on optoelectric conversion in conjugated polymers

Photoexcitation of a neutral soliton will create a polaron and a charged soliton.According to a tight-binding model and a nonadiabatic method,we investigate the dynamical process of these two photogenerated charge carriers in an external electric field.It is found that the polaron and the soliton can pass through each other,which excludes the possibility of carrier recombination that usually occurs in existing organic solar cells.The results indicate a more efficient way to realize the optoelectric conversion by photoexciting polymer materials with soliton defects.On the other hand,it is found that solitons take on greater stability than polarons during collision.     

共轭高分子链中大极化子与小极化子的弹性碰撞

基于Su-Schrieffer-Heeger(SSH)模型,考虑电子-电子相互作用,以及在哈密顿量中引入Brazovskii-Kivova对称破缺项,采用动力学演化的方法研究了在外电场作用下共轭高聚物分子链中大极化子与小极化子之间的弹性散射过程.研究发现,载流子的载荷性质不但决定大小极化子之间的相互作用性质,也深刻地影响了其发生散射后的载流子输运性质.在较低电场的作用下,当两载流子电性相同时,发生碰撞后,小极化子将推动着大极化子一起运动;而当两者电性相反时,碰撞后,大极化子将拖曳着小极化子一起运动.当电场强度超过临界值时,将产生量子隧穿效应,即,大小极化子相互迅速穿透,且不受载流子的载荷影响.     

共轭高聚物中极化子散射引起的激子迁移(英文)

基于Su-Schrieffer-Heeger(SSH)模型并考虑到Brazovskii-Kirova对称破缺项,研究了共轭聚合物中注入极化子和激子在外电场下的散射过程.研究发现在外场作用下极化子总是能通过激子,而激子的运动行为则密切依赖于电场的强度.如果电场大于临界电场3.0×10~5V/cm,那么激子与极化子散射后并不发生任何运动;然而当电场小于此临界值时,激子将在极化子运动的相反方向上有一个明显的位移.激子在弱电场下所发生的这种迁移运动,是由于同极化子发生了慢散射作用.     

金属/掺杂聚合物/金属结构中载流子的注入与输运

基于紧束缚的Su-Schrieffer-Heeger模型,利用非绝热的动力学方法,研究了金属/聚合物/金属三明治结构中载流子注入与输运的动力学过程,其中,聚合物中含有一个掺杂离子. 电子波函数随时间的演化满足含时Schrdinger方程,晶格运动满足经典的牛顿运动方程. 研究发现,掺杂离子对注入到聚合物中的载流子的作用类似一个控制阀门,阀门的状态与电场的强度和偏压的大小密切相关. 关键词： 载流子输运 波包 非绝热动力学     

共轭高聚物链中极化子生成的掺杂效应

在紧束缚近似下,用绝热动力学演化的方法研究了共轭高聚物链中低浓度掺杂对极化子生成位置的影响。研究发现,掺入杂质与注入电子的先后次序不同,极化子生成的位置会有很大差别,先注入电子后掺入杂质的情况下,在链端自由区与过渡区,极化子生成位置受杂质影响较小;而先杂质后电子的次序下,极化子的生成位置明显受到杂质的控制。该研究表明共轭高聚物链中极化子的生成位置可通过调节掺杂与电荷注入的次序加以控制,从而可达到间接改变载流子迁移率的目的。     

Formation dynamics of bipolaron in a metal/polymer/metal structure

Charge injection process from metal electrode to a nondegenerate polymer in a metal/ polymer/ metal structure has been investigated by using a nonadiabatic dynamic method. We demonstrate that the dynamical formation of a bipolaron sensitively depends on the strength of applied electric field, the work function of metal electrode, and the contact between the polymer and the electrode. For a given bias applied to one of the electrode (V₀) and coupling between the electrode and the polymer (t^′), such as V₀=0.79 eV and t^′=1 eV, the charge injection process depending on the electric field can be divided into the following three cases: (1) in the absence of the electric field, only one electron tunnels into the polymer to form a polaron near the middle of the polymer chain; (2) at low electric fields, two electrons transfer into the polymer chain to form a bipolaron; (3) at higher electric fields, bipolaron can not be formed in the polymer chain, electrons are transferred from the left electrode to right electrode through the polymer one by one accompanying with small irregular lattice deformations.     

共轭高聚物中极化子形成的自洽迭代收敛性

用自洽迭代的方法模拟了一维共轭高聚物链中极化子的形成,得出有机物链的初始晶格位形与自洽迭代收敛性的关系。对于初始晶格位形为键长有规律交错变化的一维晶格,闭链的收敛精度远高于开链的收敛精度,表明有机物链越长收敛越慢。对于闭链,降低晶格的对称性,有利于自洽迭代收敛于极化子。在有机物链中出现杂质的情况下,我们发现杂质所处的位置同收敛性密切相关,当掺杂发生在有机物链的中心附近区域时,自洽迭代单调收敛;而当掺杂发生在其它区域时,收敛过程出现波动性,导致收敛过程变慢。我们的研究表明,一维有机分子链中载流子的生成同初始晶格的位形与分子链所处的环境密切相关,这预示着在更复杂的有机物结构中,可能存在新型的复合载流子。     

共轭高聚物中极化子形成的自洽迭代收敛性

用自洽迭代的方法模拟了一维共轭高聚物链中极化子的形成,得出有机物链的初始晶格位形与自洽迭代收敛性的关系。对于初始晶格位形为键长有规律交错变化的一维晶格,闭链的收敛精度远高于开链的收敛精度,表明有机物链越长收敛越慢。对于闭链,降低晶格的对称性,有利于自洽迭代收敛于极化子。在有机物链中出现杂质的情况下,我们发现杂质所处的位置同收敛性密切相关,当掺杂发生在有机物链的中心附近区域时,自洽迭代单调收敛;而当掺杂发生在其它区域时,收敛过程出现波动性,导致收敛过程变慢。我们的研究表明,一维有机分子链中载流子的生成同初始晶格的位形与分子链所处的环境密切相关,这预示着在更复杂的有机物结构中,可能存在新型的复合载流子。     

共轭高分子链中电荷迁移的热效应

从理论上研究了共轭高聚物链中在电场作用下极化子运动的热效应.基于SSH模型以及通过绝热动力学演化的方法,模拟了共轭高聚物链中极化子在电场作用下从链左端向右端运动的过程.晶格受到的热扰动作用假设为通过局域的晶格范围内原子位移的随机涨落来实现.结果发现,晶格中的局域热涨落对于运动中的极化子而言等效于一个势垒.势垒高度由高分子中受到热扰动的区域的范围大小以及该区域与其周围环境的温差来决定.当分子中存在热吸收不均匀的现象时,链内极化子迁移率在低电场范围内随电场的变化遵循对数曲线变化规律.     

杂质离子对有机共轭聚合物中极化子动力学性质的影响

基于一维紧束缚Su-Schrieffer-Heeger模型, 采用分子动力学方法, 讨论了杂质势的强度和杂质之间的距离对电子和空穴极化子动力学性质的影响. 研究结果表明: 1)当杂质势强度保持不变时, 两杂质离子之间的距离(d)在2-16个晶格常数变化时, 电子极化子的平均速度大于空穴极化子的平均速度, 这是由于电子、空穴极化子与杂质势的库仑作用不同而产生的差异, 同时极化子的平均速度随d的增加而增大; 若继续增加杂质离子之间的距离, 电子和空穴极化子的平均速度几乎保持不变, 仅有一些微小的振荡, 这是由于不同距离的杂质离子对电子和空穴极化子产生的势垒或势阱的叠加效果不同而引起的; 2)保持两杂质离子之间的距离不变时, 随着杂质势强度的增大, 电子和空穴极化子的平均速度均减小, 且空穴极化子的平均速度减小趋势更明显.     

有机高分子链内的场致激子解离

基于SSH(Su-Schrieffer-Heeger)模型,采用静态及动力学自洽算法模拟了有机高分子链内激子在光激发及外电场作用下的形成与解离过程。结果表明,受光激发后,有机高分子链内激子的生成与解离密切依赖于施加外电场的时机,当外电场与光激发同时发生时,激子能否生成完全取决于电场强度的大小;而当外电场在光激发后的一段时间(通常为皮秒量级)之后被引入,则在有机高分子链内能够形成稳定的激子,且该激子只有在强外电场(超过1MV/cm)的作用下,才会发生解离,临界场强量级与实验结果相符合。     

Polaron dynamics in a system of coupled conjugated polymer chains

The motion of excitations such as polarons is believed to be of fundamental importance for the transport properties of conjugated polymers for the use in, e.g., polymer based LED's. We have investigated polaron dynamics in a system of coupled polymer chains in the presence of an external electric field. In particular, we focus on how a polaron migrates through the polymer lattice, i.e., the situation in which a polaron reaches a chain end and is scattered to the surrounding chains. We show that the outcome of this event strongly depends on the strength of the electric field, and we identify three different cases for the polaron migration.     

Electron–phonon effect on the ground-state binding energy of hydrogenic impurity in quantum-well wire in presence of an electric field

The hydrogenic impurity binding energy in rectangular quantum well wire including both barriers of finite height and an applied electric field are studied. The polaron effects on the ground-state binding energy in electric field are investigated by means of Landau-Pekar variation technique. The results for the binding energy as well as polaronic correction are obtained as a function of the size of the wire, the applied electric field and the position of the impurity. Our calculations are compared with previous results in quantum wires of comparable dimensions.     

Dynamics of Polaron at Polymer/Polymer Interface

The migration of a polaron at polymer/polymer interface is believed to be of fundamental importance for the transport and light-emitting properties of conjugated polymer-based light emitting diodes. Based on the one- dimensional tight-binding Su-Schrieffer-Heeger （SSH） model, we have investigated polaron dynamics in a one- dimensional polymer/polymer system by using a nonadiabatic evolution method. In particular, we focus on how a polaron migrates through the conjugated polymer/polymer interface in the presence of external electric field. The results show that the migration of polaron at the interface depends sensitively on the hopping integrals, the potential barrier induced by the energy mismatch, and the strength of applied electric field which increases the polaron kinetic energy.     

Polaron effects on the binding energy of a double donor impurity in quantum wells in an electric field

The binding energy of the single and double bound polaron bound to a helium-type donor impurity in quantum wells (QWs) subject to a perpendicular electric field are calculated by a variational method. The couplings of an electron and the impurity with various phonon modes are considered. The results show that the cumulative effects of the electron–phonon coupling and the impurity–phonon coupling can contribute appreciably to the binding energy for the single bound polaron but only in some severe conditions for the double bound polaron. They also show that the binding energy is sensitive to the electric field strength. The comparison between the binding energies in the case of the impurity placed at the quantum well center and at the quantum well edge is also given.     

共轭聚合物中均匀无序对极化子输运动力学的影响

基于扩展的Su-Schrieffer-Heeger紧束缚模型和非绝热动力学方法, 研究了共轭聚合物材料中均匀无序效应对极化子输运动力学的影响. 研究发现: 极化子的动力学输运过程由外加电场和均匀无序效应共同决定; 在大部分电场范围下, 均匀无序效应对极化子输运的影响不太明显, 几乎可以忽略; 但在弱电场下, 均匀无序效应不利于极化子输运. 与高斯型无序效应下极化子的输运过程相比, 具有均匀无序的薄膜形貌更有利于极化子输运.     

共轭高分子链中极化子间相互作用对电荷迁移率的影响

基于综合考虑了电子与声子以及电子与电子相互作用的理论模型,采用数值方法计算了在外电场作用下共轭高聚物分子中电荷的迁移率,讨论了大小极化子共存并相互作用对分子链内电荷迁移率的影响。研究发现,电荷迁移率明显受大小极化子的载荷性质的影响,当大小极化子具有相同电性时,在低电场范围内,分子内电荷迁移率由大极化子运动性质主导,而在高电场范围内,分子内电荷迁移率由小极化子主导;另一方面,当大小极化子具有相反电性时,电荷迁移率只由大极化子运动性质主导,与电场强度无关。此外,还讨论了电子与电子相互作用对电荷迁移率"的影响。     

二维链间扩展的极化子动力学研究

基于扩展的SSH模型,研究了有序耦合聚合物链系统中的极化子动力学,包括极化子的形成过程及其在外场下的输运.发现,当聚合物链间的耦合较强时,注入到系统中的电子会诱发二维链间扩展的极化子态,分布在多条聚合物链上.另外,动力学模拟表明,与一维链内定域极化子相比,在相同的电场强度下二维极化子具有更大的运动速度,这与实验结果一致. 关键词： 链间扩展极化子 链间耦合     

Bound polaron in a spherical quantum dot under an electric field

A variational approach is used to study the ground state of a bound polaron in a spherical quantum dot under an external electric field. The binding energy of the hydrogenic impurity state is calculated by taking the interaction of an electron with both the confined longitudinal optical phonons and the surface optical phonons into account. The interaction between impurity and longitudinal optical phonons has also been considered to obtain the binding energy of a bound polaron. It shows that the polaron effects give significant corrections to the binding energy and its Stark energy shift. The external electric field increases the phonon contributions to the binding energy.     

共轭聚合物中链内无序效应对极化子输运的影响

基于扩展的Su-Schrieffer-Heeger紧束缚模型, 利用非绝热动力学方法研究了链内无序效应对共轭聚合物中极化子输运机制的影响. 研究发现, 极化子的输运由外加电场和链内无序效应共同作用的结果所决定. 在一般情况下, 链内无序效应不利于极化子的输运, 但随着电场强度的增大, 无序对极化子输运的影响减小. 关键词： 共轭聚合物 极化子输运 链内无序