1,4-二酮吡咯并吡咯在聚合物太阳能电池的应用

1,4-二酮吡咯并吡咯(DPP)由于具有优异的共平面性和强烈的拉电子能力,从而被引入D-A型窄带隙共轭聚合物中调控聚合物材料的能隙和能级结构,拓宽在可见光区域的响应范围。近年来,DPP类聚合物太阳能电池材料的研究受到广泛关注,目前基于DPP的聚合物太阳能电池效率高已达9.64%。本文探讨了以DPP作为受体单元而噻吩衍生物、芴、咔唑和苯并二噻吩等作为给体单元制成的D-A型窄带隙共轭聚合物太阳能电池的研究进展,并探讨了聚合物材料结构与太阳能电池性能之间的内在构效关系。     

基于苯并二噻吩和吡咯并吡咯二酮共聚物的有机太阳能电池给体材料光伏性质理论研究

设计和合成结构新颖的聚合物太阳能电池给体材料是有机电子学的热点研究领域. 首先利用二噻吩取代的苯并二噻吩(DBDT)作为富电子结构单元, 吡咯并吡咯二酮(DPP)作为缺电子单元构筑了一种新的聚合物太阳能电池电子给体材料(PDBDTDPP), 然后以[6,6]-苯基-C₆₁-丁酸甲酯(PC₆₁BM)作为电子受体, 借助密度泛函理论(DFT)方法结合不相干的Marcus-Hush电荷传输模型, 系统研究了PC₆₁BM-DBDTDPP_n=1,2,3,∞体系的分子结构、电子性质、光吸收性质、电荷转移的内重组能和外重组能、激子结合能、电荷传输积分、给体-受体界面上激子分离和电荷复合速率等性质, 并利用线性回归方法分析了聚合物重复单元与其光伏性质的关系. 结果表明, 该聚合物具有较好的平面结构, 低的最高占据分子轨道(HOMO)能级, 在紫外-可见区具有宽且强的光学吸收、较大的激子束缚能(1.365 eV), 小的激子分离内重组能(0.152 eV)和电荷复合内重组能(0.314 eV). 在给体-受体界面上, 激子分离速率高达1.073×10¹⁴ s^-1, 而电荷复合速率仅为1.797×10⁸ s^-1. 相比较而言, 激子分离速率比电荷复合速率高约6个数量级, 表明在给体-受体界面上, 光生激子具有很高的分离效率. 总之, 研究证明PDBDTDPP是一个非常有前途的聚合物太阳能电池给体材料, 值得实验上进一步合成及器件化研究. 理论研究不仅有助于更深入理解有机化合物结构与其光学、电子性质之间的关系, 还可以为合理设计聚合物太阳能电池给体材料提供有价值的参考.     

哒嗪并吡咯二酮共轭聚合物半导体材料的合成及晶体管性能

采用Stille交叉偶联反应,合成了基于6-烷基吡咯[3,4-d]哒嗪-5,7-二酮(PPD)与吡咯并吡咯二酮(DPP)结构单元的受体-π-受体(A_1-π-A_2)型共轭聚合物(PPPD-DPP)。采用热重分析仪、紫外分光光度计、电化学工作站等表征了聚合物PPPD-DPP的性能,系统地研究了聚合物的热性能、光物理性能、电化学性能及晶体管性能。结果表明:聚合物PPPD-DPP具有良好的热稳定性,热分解温度达到376℃;薄膜的最大吸收峰位于702nm,光学能带隙为1.27eV;有较低的最高占据分子轨道能级(HOMO,-5.23eV)。基于PPPD-DPP的有机薄膜晶体管(OTFTs)器件在真空中显示出双极性传输特性,最高电子和空穴迁移率分别为0.030 cm~2/(V·s)和0.054cm~2/(V·s),在空气中PPPD-DPP器件则表现出明显的p型传输特性,空穴迁移率提升至0.121cm~2/(V·s)。     

含噻吩[2,3-b]并噻吩-吡咯[3,4-c]并吡咯二酮结构单元聚合物的合成及其在太阳能电池中的应用研究

设计并合成了一种交叉共轭的(cross-conjugated)缺电子型聚合物单体——二溴代噻吩[2,3-b]并噻吩-吡咯[3,4-c]并吡咯(DPPTTZ)二酮,并将其分别与噻吩(T)、硒吩(Se)和N-甲基吡咯(Py)的双锡试剂进行共聚反应,获得了一类新的供体-受体(D-A)型共轭聚合物光电材料.这类材料分子的最高占有轨道(HOMO)能级较低,因此其光电器件具有较高的开路电压(Voc),稳定性好.此外,它们在紫外-可见光区有较宽的吸收,最大吸收位于波长620 nm附近;能带隙(band gap)小,分别为1.86 e V(p DPPTTZ-T)、1.83 e V(p DPPTTZ-Se)和1.85 e V(p DPPTTZ-Py).器件初步测试结果表明,上述聚合物与PC71BM组成的本体异质结聚合物太阳能电池Voc在0.68~0.81 V之间,能量转化效率(PCE)最高达3.05%(p DPPTTZ-T).     

从导电聚吡咯到共轭聚合物光伏材料——我在中科院化学所30年共轭高分子研究历程

本文简要回顾了本人在中科院化学所30年的研究历程,重点介绍了在共轭高分子(包括导电聚吡咯电化学、聚合物发光电化学池(LEC)和共轭聚合物给体光伏材料)方面的研究成果。在导电聚吡咯电化学方面,对导电聚吡咯的电化学制备和电化学性质进行了深入研究,阐明了各种电化学聚合条件对制备的导电聚吡咯电导和力学强度等的影响,发现电解液溶剂给电子性(Donor number)对吡咯电化学聚合制备的导电聚吡咯电导的影响:溶剂Donor number越小制备的导电聚吡咯电导越高;使用非离子表面活性剂添加剂在水溶液中制备出表面非常光滑和高力学强度的导电聚吡咯薄膜;对于吡咯电化学聚合提出了电解液阴离子参与的阳离子自由基聚合机理,并推到出吡咯电化学聚合反应的动力学方程;发现在NaNO3水溶液中电化学聚合制备的导电聚吡咯除存在主链氧化、对阴离子掺杂结构外,还存在质子酸掺杂结构;阐明了导电聚吡咯在水溶液中电化学还原和再氧化的机理及其电化学过程的可逆性和稳定性,以及导电聚吡咯在有机电解液中特殊的第一次还原和再氧化的机理。在LEC方面,通过交流阻抗法确认了LEC的电化学掺杂机理和p-i-n结构,合成了多种适用于LEC的主链带离子导电单元的兼具离子导电性的发光嵌段共聚物,避免了LEC活性层中存在的发光聚合物和离子导电聚合物的分相问题;使用离子液体作为电解质制备了室温准冷冻p-i-n结LEC,改善了LEC的电致发光性能。在共轭聚合物给体光伏材料方面,我们提出了通过共轭侧链来拓宽聚合物吸收和提高空穴迁移率的分子设计思想,设计和合成了一系列带共轭侧链的二维共轭聚噻吩衍生物以及基于二噻吩取代苯并二噻吩的窄带隙高效二维共轭聚合物给体光伏材料。我们使用烷硫基取代进一步降低了这类二维共轭聚合物的HOMO能级从而进一步提高了其光伏性能。最后介绍了本组二维共轭聚合物给体光伏材料在非富勒烯聚合物太阳能电池方面的最新研究进展。     

侧链含自由基单元的1,4-吡咯并吡咯二酮共轭聚合物的合成和半导体性质研究

合成了两个侧链含有2,2,6,6-四甲基哌啶-1-氧自由基单元(TEMPO)的1,4-吡咯并吡咯二酮(DPP)共轭聚合物PDPP4T-1和PDPP4T-2,并开展了其半导体性质研究。薄膜场效应晶体管器件测试结果显示,相对于不含TEMPO的聚合物PDPP4T,PDPP4T-1和PDPP4T-2的场效应器件性能有所降低,不过,含TEMPO的聚合物器件性能最高仍达到了2.12cm~2·V~(-1)·s~(-1)。进一步通过原子力显微镜和X射线衍射对TEMPO引入后导致性能降低的可能原因进行了研究。     

基于吡咯并吡咯二酮的D-A化合物的合成及其光学性质研究

通过Suzuki反应,在噻吩取代吡咯并吡咯二酮(DPP)的两端引入不同的电子给受体,成功构建了一系列基于吡咯并吡咯二酮的D-π-A化合物.通过核磁共振谱、紫外-可见吸收光谱、荧光光谱、循环伏安结合理论计算对这一系列化合物进行了表征.通过对比发现,随着分子共轭长度的增加,其紫外吸收呈现较明显的红移,最大移动到近红外区(650nm).电化学研究表明,该类化合物具有较低的能级.光学以及电化学性质研究表明,该DPP类化合物可以作为构建有机电子学方面的重要材料,特别是在有机太阳能电池方面具有潜在的应用.     

基于二噻吩并吡咯π桥的窄带隙非富勒烯受体材料在有机太阳能电池中的应用

以不同烷基取代的二噻吩并吡咯(DTP)为π桥,连接吲哒省并二噻吩(IDT)中间单元和氰基茚酮(IC)或二氟代氰基茚酮(2F-IC)末端基团,设计并合成了6个窄带隙的非富勒烯受体材料。 其中,IDTDTP-C₂C₂-H和IDTDTP-C₂C₂-F中的DTP单元以1-乙基丙基为侧链,IDTDTP-C₆C₆-H和IDTDTP-C₆C₆-F中的DTP单元以1-己基庚基为侧链,IDTDTP-C₁₂-H和IDTDTP-C₁₂-F中的DTP单元以十二烷基为侧链。 6个分子均具有较窄的光学带隙(1.37~1.44 eV)。 相比于以IC为末端基团的分子(IDTDTP-C₂C₂-H、IDTDTP-C₆C₆-H和IDTDTP-C₁₂-H),由于氟原子的拉电子效应,以2F-IC为末端基团的分子(IDTDTP-C₂C₂-F、IDTDTP-C₆C₆-F和IDTDTP-C₁₂-F)具有红移的吸收光谱,以及更低的最高分子占有轨道能级(HOMO)和最低分子空轨道(LUMO)能级。 以宽带隙聚合物聚[2,6-(4,8-双(5-(2-乙基己基))噻吩-2-基)-苯并[1,2-b:4,5-b']二噻吩-alt-5,5-(1',3'-二-2-噻吩)-5',7'-双(2-乙基己基)-苯并[1',2'-c:4',5'-c']二噻吩-4,8-二酮](PBDB-T)为给体材料,制备了有机太阳能电池器件。 PBDB-T:IDTDTP-C₆C₆-F共混薄膜具有较高且更平衡的空穴/电子迁移率,以及良好的形貌,基于PBDB-T:IDTDTP-C₆C₆-F的有机太阳能电池获得了6.94%的能量转换效率,开路电压为0.86 V,短路电流密度为13.56 mA/cm²,填充因子为59.5%。     

聚吡咯并[3,4-c]吡咯的电子结构及导电性研究

采用密度泛函(DFT)方法在6-31g(d)水平下研究了聚吡咯和聚吡咯并[3,4-c]吡咯, 以及它们的单体和低聚物的电子结构. 对中心键的键长、电荷密度以及Weberg键级的研究表明, 随着主链聚合度的增加, 其共轭性增强. 对聚合物还进行了能带结构和态密度分析. 结果发现, 在3位聚合的并环化合物具有最优的导电性能, 其能隙仅有0.25 eV, 可以作为潜在的导电聚合物材料.     

窄带隙二噻吩并吡咯共聚物合成与光伏性能研究

二噻吩[3,2-b:2′,3′-d]并吡咯(Dithieno[3,2-b:2′,3′-d]pyrrole,DTP)分别与3种受体单元聚合得到聚合物P1~P3,受体单元分别为:吡咯并吡咯二酮(DPP)、二噻吩苯并噁二唑(DTBO)和喹喔啉衍生物(TQ).研究表明,3种聚合物都有较窄的带隙(P1:1.23 e V,P2:1.51 e V,P3:1.50 e V),有利于活性层材料对太阳光的吸收,其中P1获得了最宽的吸收(近1000 nm).将P1~P3与PC71BM共混制备光伏器件,当给受体比例为1∶3时,基于P1的光伏器件短路电流密度(short-circuit current density,JSC)为15.82 m A/cm~2,开路电压(open-circuit voltage,VOC)为0.38 V,能量转化效率(power conversion efficiency,PCE)达到3.33%,为3种聚合物中最高的效率.对于聚合物P2和P3,在给受体比例为1∶2时,光伏性能最好,此时P2与P3的PCE值分别为1.20%和1.37%,导致较低光电转换效率的因素是短路电流密度JSC(P2:9.70 m A/cm~2,P3:9.21 m A/cm~2)和开路电压VOC(约0.3 V)过低.     

Influence of Backbone Chlorination on the Electronic Properties of Diketopyrrolopyrrole (DPP)‐Based Dimers

Chlorination of π‐conjugated backbones is garnering great interest because of fine‐tuning electronic properties of conjugated materials for organic devices. Herein we report a synthesis of thiophene‐based diketopyrrolopyrrole (DPP) dimers and their chlorinated counterparts by introducing a chlorine atom in the outer thiophene ring to investigate the influence of the chlorination on charge transport. The backbone chlorination lowers both the HOMO and the LUMO of the dimers and leads to a blue‐shift of maximum absorption in compared to unsubstituted counterparts. X‐ray analysis reveals that the chlorine atom prompts the outer thiophene ring out of the planarity of the backbone with a relatively large torsional angle. The chlorinated dimers exhibit slipped one‐dimensional packing decorated with multiple intermolecular interactions, because of a combination of a negative inductive effect and a positive mesomeric effect of the halogen atom, which might facilitate charge transport within the oligomeric backbones. The mobility in the single‐crystal OFET devices of the chlorinated dimers is up to 1.5 cm² V^?1 s^?1, which is two times higher than that of the non‐chlorinated DPP dimers. Our results indicate that the chlorine atom plays a key role in directing non‐covalent interactions to lock the slipped stacks, enabling electronic coupling between adjacent molecules for efficient charge transport. In addition, our results also demonstrate that these DPP dimers with straight n‐octyl chains exhibit higher mobilities than the dimers with branched 2‐ethylhexyl chains.     

Impact of replacement of the central benzene ring in anthracene by a heterocyclic ring on electronic excitations and reorganization energies in anthratetrathiophene molecules

The impact of changing the central benzene ring on the electronic excitations and reorganization energies (λ) of the anthratetrathiophene (ATT) molecules is studied by density functional theory (DFT) and time‐dependent DFT (TD‐DFT) quantum chemical calculations. The effect of changing the position of the sulfur atom at the periphery of anthracene on the optical and charge transfer properties is also studied. The calculated results suggest that the HOMO, LUMO, HOMO–LUMO energy gap, ionization potential (IP), electron affinity (EA), hole extraction potential (HEP), electron extraction potential (EEP), and reorganization energies (λ) are affected by replacing the central ring with different heterocyclic rings and the position of the sulfur atom. In addition, all molecules show good hole‐ and electron‐transport properties. This work may be helpful for future design and preparation of high‐performance charge‐transport materials.     

The impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of the fused thiophene semiconductors

The charge transport properties of 3 fused thiophene semiconductors, end-capped with diperfluorophenylthien-2-yl (DFPT) groups (DFPT-thieno[2′, 3′:4, 5]thieno[3, 2-b]thieno[2, 3-d]thiophene (TTA), DFPT-dithieno[2, 3-b:3′, 2′-d]thiophenes (DTT), and DFPT-thieno[3, 2-b]thiophene (TT)), are explored via density functional theory (DFT). To gain a better understanding of the impact of diperfluorophenyl and thienyl substituents on the electronic structures and charge transport properties of these molecules, the geometric structures, reorganization energy, frontier molecular orbitals, molecular ionization potentials and electron affinities, absorption spectra of the corresponding molecules including diperfluorophenyl (DFP)-TTA, DFP-DTT, DFP-TT, dithienyl (DT)-TTA, DT-DTT, DT-TT as well as their parent molecules (TTA, DTT and TT) are investigated for comparison. The calculated results show that introducing perfluorophenyl groups to the fused thiophenes could be a good strategy to promote electron transport, while the insertion of additional thiophene rings to DFP-end-capped derivatives could further extend the π-conjugation and enhance the charge transport properties of DFPT-end-capped analogs.     

Computational study of structure,electronic, and microscopic charge transport properties of small conjugated diketopyrrolopyrrole‐thiophene molecules

π‐Conjugated small molecules containing diketopyrrolopyrrole (DPP) and thiophene moieties represent a modern class of functional materials that exhibit promising charge transport properties and therefore have great potential as building blocks of active elements of electronic devices. As a starting point of this computational study, the molecular structure, electronic characteristics, and reorganization energies associated with electron or hole transfer are considered. Prediction of molecular crystal packing is followed by the calculation of couplings between adjacent molecules and detection of the effective charge transfer pathways. Finally, the rates of charge transfer process are evaluated. The obtained results shed light not only on the properties of materials containing low‐molecular species but also serve as a benchmark for further classical force‐field simulations of DPP‐based polymers.     

Charge Transport and Conductance Switching of Redox‐Active Azulene Derivatives

Azulene (Az) is a non‐alternating, aromatic hydrocarbon composed of a five‐membered, electron‐rich and a seven‐membered, electron‐poor ring; an electron distribution that provides intrinsic redox activity. By varying the attachment points of the two electrode‐bridging substituents to the Az center, the influence of the redox functionality on charge transport is evaluated. The conductance of the 1,3 Az derivative is at least one order of magnitude lower than those of the 2,6 Az and 4,7 Az derivatives, in agreement with density functional theory (DFT) calculations. In addition, only 1,3 Az exhibits pronounced nonlinear current–voltage characteristics with hysteresis, indicating a bias‐dependent conductance switching. DFT identifies the LUMO to be nearest to the Fermi energy of the electrodes, but to be an active transport channel only in the case of the 2,6 and the 4,7 Az derivatives, whereas the 1,3 Az derivative uses the HOMO at low and the LUMO+1 at high bias. In return, the localized, weakly coupled LUMO of 1,3 Az creates a slow electron‐hopping channel responsible for the voltage‐induced switching due to the occupation of a single molecular orbital (MO).     

卤素、 氰基及N原子修饰对四硫富瓦烯衍生物载流子传输性质影响的理论研究

基于密度泛函理论结合跳跃模型和能带理论研究了氟、 氯、 氰基和N原子的引入对四硫富瓦烯(TTF)衍生物载流子传输性质的影响. 计算结果表明, 嵌N修饰会降低分子重组能, 特别是当N原子靠近TTF主体环时作用更明显. 与引入卤素修饰相比, 引入氰基修饰的分子具有更小的电子和空穴重组能及更低的前线分子轨道(FMO)能级. 同时迁移率的计算结果显示, 分子6具有1.15 cm²·V^-1·s^-1的高电子迁移率, 考虑其较低的LUMO能级, 推测其有望成为潜在的优异电子传输材料, 而相似的电子和空穴迁移率使分子2有望成为潜在的双极性传输材料. 同时还考察了S和N原子之间的弱相互作用, 当S或N原子对分子HOMO(或LUMO)有贡献时, 其相应的空穴(或电子)传输能力会有所提高.     

A theoretical study of the charge transfer behavior of the highly regioregular poly-3-hexylthiophene in the ordered state

We use quantum mechanical (QM) methods to interpret the charge transport properties of the self-assembled poly-3-hexylthiophene (P3HT) molecules along the intrachain and interchain directions. Our approach is illustrated by a hopping transport model, in which we examine the variation of the electron-coupling strength (transfer integral) with the torsional angle and the intermolecular distance between two adjacent thiophene segments. We also simulate the packed P3HT structures at various values of temperature and regioregularity via the molecular dynamics (MD) simulations. The MD results indicate that with decreasing the molecular regioregularity and/or increasing temperature, the P3HT backbone chains experience a larger distortion of the thiophene rings out of coplanarity, and thus the charge mobility along the main chains is reduced. However, as long as the P3HT molecules remain in the ordered lamellar state due to the presence of the pi-pi interaction, the resultant mobility along the pi-pi interchain direction is still significantly less than that along the intrachain direction. Accordingly, the main charge transfer route within the P3HT ordered domains is along the intrachains instead of the interchains.     

Density functional theory study on electron and hole transport properties of organic pentacene derivatives with electron-withdrawing substituent

Attaching electron-withdrawing substituent to organic conjugated molecules is considered as an effective method to produce n-type and ambipolar transport materials. In this work, we use density functional theory calculations to investigate the electron and hole transport properties of pentacene (PENT) derivatives after substituent and simulate the angular resolution anisotropic mobility for both electron and hole transport. Our results show that adding electron-withdrawing substituents can lower the energy level of lowest unoccupied molecular orbital (LUMO) and increase electron affinity, which are beneficial to the electron injection and ambient stability of the material. Also the LUMO electronic couplings for electron transport in these pentacene derivatives can achieve up to a hundred meV which promises good electron transport mobility, although adding electron-withdrawing groups will introduce the increase of electron transfer reorganization energy. The final results of our angular resolution anisotropic mobility simulations show that the electron mobility of these pentacene derivatives can get to several cm(2) V(-1) s(-1), but it is important to control the orientation of the organic material relative to the device channel to obtain the highest electron mobility. Our investigation provide detailed information to assist in the design of n-type and ambipolar organic electronic materials with high mobility performance.     

Intermolecular H···O═C bonds induced 2D self‐assembly of thiophene based diketopyrrolopyrrole derivative

Compounds with diketopyrrolopyrrole (DPP) and thiophene moieties have attracted considerable attention because of their promising charge transport properties. The molecular conformation and self‐assembly of 2,5‐dihexadecyl‐3,6‐di(thiophen‐2‐yl)‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione (TDPP‐C16) molecule have been investigated by scanning tunneling microscopy and density functional theory alculation. The TDPP‐C16 molecules adsorb with their optimized S‐shaped conformation and form a zipper‐like pattern on highly oriented pyrolytic graphite surface. R and S rotated structures are observed. The nanostructure is dominated by intermolecular double hydrogen bonds between C═O of the DPP units and hydrogen atom of thiophene rings in the neighboring molecules in each row. Atomic force microscopy and density functional theory calculation also display the existence of strong intermolecular hydrogen bonding. The results provide molecular evidence for the intermolecular interactions of the surface structure, which could benefit to the design of the organic semiconducting materials and understanding of underlying principle of charge transfer process. Copyright © 2017 John Wiley & Sons, Ltd.     

巯基偶氮苯单分子电子传输的取代基效应

用密度泛函理论B3LYP/6-31G**计算巯基偶氮苯分子及分子离子的空间构型和电子结构, 研究取代基对巯基偶氮苯单分子电子传输的影响. 结果表明, 拉电子基(—COOH、—NO2)的引入, 可以提高巯基偶氮苯单分子电子传输体系的稳定性, 使体系LUMO的离域性增高、S原子反应活性增强、HOMO-LUMO能隙显著减小, 进而降低电子传输能垒, 有利于分子电子传输. 相同取代基的分子离子比分子具有更小的HOMO-LUMO能隙, S—Au键更易形成, 金属-分子-金属结构的电子传输性更强.