Insight into the Excited State Electronic and Structural Properties of the Organic Photovoltaic Donor Polymer Poly(thieno[3,4-b]thiophene benzodithiophene) by Means of ab Initio and Density Functional Theory,The Journal of Physical Chemistry C

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Insight into the Excited State Electronic and Structural Properties of the Organic Photovoltaic Donor Polymer Poly(thieno[3,4-b]thiophene benzodithiophene) by Means of ab Initio and Density Functional Theory
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-09-16 00:00:00 , DOI: 10.1021/acs.jpcc.6b07689
Itamar Borges _{1,

2,

3} , Elmar Uhl ₃ , Lucas Modesto-Costa ₂ , Adélia J. A. Aquino ₁ , Hans Lischka _{1,

4}

Affiliation

Structural and electronic properties of the ground and lowest excited states of the electron-donor conjugated copolymer poly(thieno[3,4-b]thiophene benzodithiophene) (PTB1) are reported based on high-level theoretical investigations. PTB1 combined with phenyl-C₆₁-butyric acid methyl ester (PCBM) results in a bulk heterojunction blend with promising properties for use in organic solar cells. The ab initio algebraic diagrammatic construction method to second order, ADC(2), was used to obtain benchmark data for excited state energies, oscillator strengths, and bond length alternation (BLA) analysis. Time dependent density functional theory (TDDFT) calculations using the exchange-correlation functionals PBE, B3LYP, BHandHLYP, CAM-B3LYP, and LC-wPBE were also performed and compared with ADC(2) calculations. It was shown that a minimum of 20% Hartree–Fock exchange in the functional is necessary to reproduce the major features of the ADC(2) results. Analysis of the BLA results indicates the possibility of exciton trapping by geometry relaxation occurring in the middle of the polymer chain. The corresponding exciton binding energy is about 0.4 eV. Charge distributions in the ground and lowest excited singlet state were analyzed as well. The natural population analysis (NPA) confirms the electronegative character of the benozodithiophene group and the corresponding positive one of the thienothiophene moiety leading to an alternant chain polarization of positive and negative charges. Electron density differences between the S₀ and S₁ states show a transfer of electron density from double bond regions to areas of single bonds, a feature which parallels nicely the lengthening of double bonds and shortening of single bonds in the S₁ state.

中文翻译：

从头算和密度泛函理论洞察有机光伏给体聚合物聚噻吩并[3,4- b ]噻吩苯并二噻吩的激发态电子和结构性质

基于高水平的理论研究，报道了电子给体共轭共聚物聚（噻吩并[3,4- b ]噻吩苯并二噻吩）（PTB1）的基态和最低激发态的结构和电子性能。将PTB1与苯基C ₆₁丁酸甲酯（PCBM）结合使用，可得到具有良好前景的本体异质结共混物，可用于有机太阳能电池。该从头二阶的代数图解构造方法ADC（2）用于获得激发态能量，振荡器强度和键长交替（BLA）分析的基准数据。还使用交换相关函数PBE，B3LYP，BHandHLYP，CAM-B3LYP和LC-wPBE进行了时变密度泛函理论（TDDFT）计算，并将其与ADC（2）计算进行了比较。结果表明，功能上至少要进行20％的Hartree-Fock交换才能重现ADC（2）结果的主要特征。对BLA结果的分析表明，在聚合物链的中间会发生因几何弛豫而引起的激子俘获。相应的激子结合能约为0.4 eV。还分析了基态和最低激发单重态的电荷分布。自然种群分析（NPA）确认了苯并二噻吩基和相应的噻吩并噻吩部分的正电性，从而导致正电荷和负电荷交替发生链极化。电子密度之间的差异S ₀和S ₁状态显示出电子密度从双键区域到单键区域的转移，这一特征与S ₁状态下双键的延长和单键的缩短很好地平行。

更新日期：2016-09-16

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