Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences
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共轭聚合物前线轨道能级调控与光伏性能研究
No full text延伸聚合物π共轭体系和在聚合物结构中引入氟是两种改善聚合物光伏性能的方法。目前广泛使用噻吩延伸共轭体系，这种方法通常会抬高聚合物的最高占有轨道（HOMO）能级，不利于形成大的开路电压。在聚合物结构中引入氟可以降低聚合物的HOMO能级，但很多情况下聚合物的HOMO能级比最低空轨道（LUMO）能级降得更多，导致聚合物的带隙变大，不利于吸收更多的光子。本论文围绕着调控聚合物的前线轨道（HOMO和LUMO）能级开展了一系列工作，主要研究内容包括两个方面：一、研究既能延伸聚合物共轭体系又能降低聚合物HOMO能级的方法；二、设计既具有低的HOMO能级，又具有小的光学带隙的含氟聚合物。这两个方面的研究内容具体如下：
1. 我们用苯环延伸烷噻吩基苯并二噻吩聚合物的共轭体系。与噻吩相比，苯环是缺电子的。并上苯环后聚合物的HOMO和LUMO能级分别从-5.36 eV和-3.60 eV降低到-5.47 eV和-3.73 eV，光学带隙从1.76 eV降低到1.74 eV，吸收边红移至713 nm。除此之外，聚合物分子间的相互作用力大大加强，热稳定性也有所提高。并上苯环后聚合物的光伏性能有明显提高，器件的短路电流密度从9.83 mA/cm2提高到12.93 mA/cm2，能量转换效率从5.35%提高到7.30%。
2. 我们用苯环延伸烷氧苯基苯并二噻吩聚合物的共轭体系。并上苯环后，聚合物的HOMO和LUMO能级得到显著降低，分别从-5.23 eV和-3.51 eV降低到-5.49 eV和-3.78 eV，而聚合物的光学带隙基本维持不变，为1.71 eV。并上苯环后聚合物的光伏性能有小幅提高，器件的开路电压从0.83 V提高到0.84 V，短路电流密度从11.33 mA/cm2提高到12.29 mA/cm2，能量转换效率从6.23%提高到6.57%。
3. 我们把两个噻吩并在苯并噻二唑（BT）上设计了一个新的稠环结构单元——二噻吩并苯并噻二唑（fDTBT）。我们将具有曲折结构的fDTBT 和含有长“撑开”侧链的引达省并二噻吩（IDT）组合在一起构建了聚合物PIDT-fDTBT。PIDT-fDTBT是研究曲折度对聚合物光伏性能影响的理想模型。与基于BT的聚合物相比，PIDT-fDTBT的HOMO能级下降了0.08 eV，LUMO能级上升了0.2 eV，光学带隙增大到2.03 eV。PIDT-fDTBT光伏器件的开路电压得到明显改善，达到了0.90 V，但由于带隙太宽，短路电流密度减小，导致能量转换效率降低。
4. 我们将fDTBT中BT单元上的硫换成氧，合成了一个具有较强吸电子能力的曲折结构受体二噻吩并苯并噁二唑（fDTBO）。我们将fDTBO分别与烷氧基苯并二噻吩和烷噻吩基苯并二噻吩单体共聚合成了聚合物PBDTO-fDTBO与PBDTT-fDTBO。这两个聚合物的光学带隙分别是2.00 eV和1.95 eV。PBDTO-fDTBO与PBDTT-fDTBO均展现了非常深的HOMO能级，分别达到了-5.58 eV和-5.60 eV。因此，基于这两个聚合物的光伏器件的开路电压都很大，均超过了1 V。
5. 我们首次将氟引入吡啶并噻二唑（PT）聚合物结构中。含氟的PT聚合物（PDTPT-2TF）的HOMO和LUMO能级分别为-5.34 eV和-3.89 eV，与不含氟的PT聚合物（PDTPT-2T）相比，分别降低了0.11 eV和0.15 eV。PDTPT-2TF光学带隙为1.45 eV，降低了0.04 eV。X射线衍射分析表明氟使聚合物固态结构更规整。引入氟之后聚合物的光伏性能得到大幅改善。PDTPT-2T器件的能量转换效率最大值仅为2.65%，其中开路电压为0.73 V，短路电流密度为5.34 mA/cm2，填充因子为67.91%。PDTPT-2TF器件的能量转换效率最大值为8.01%，相应的开路电压为0.74 V，短路电流密度为15.52 mA/cm2，填充因子为69.73%。8.01%的能量转换效率是基于PT的聚合物太阳能电池的最高能量转换效率，而且这个能量转换效率是在没有使用添加剂以及退火等后处理的条件下实现的。
本论文的研究成果表明：一、用苯环延伸聚合物的共轭体系和增大聚合物主链的曲折度是两种既能延伸聚合物共轭体系又能降低聚合物HOMO能级的有效方法；二、在DTPT-2T聚合物中引入氟既可以降低聚合物的HOMO能级又可以减小聚合物的光学带隙。本论文对于完善有机电子学理论有着重要意义。Extending π-conjugation system and incorporating fluorine substituent into polymer chains are two effective methods to improve their photovoltaic properties. Currently thiophene is widely used to extend the π-conjugation system of conjugated polymers. But this method usually results in a higher highest occupied molecular orbital (HOMO) energy level, which is unfavorable to realizing a high open-circuit voltage (Voc) in photovoltaic devices. Incorporating fluorine substituent into polymer chains could down-shift their HOMO levels, but in many cases their optical bandgaps are increased due to the less down-shifts of the lowest unoccupied molecular orbital (LUMO) levels. Large bandgaps are unfavorable for polymers to harvest more light. This dissertation focuses on tuning the frontier molecular orbitals (HOMO and LUMO) of photovoltaic polymers: (i) To explore the method to simultaneously extend the π-conjugation system and down-shift the HOMO level of a polymer; (ii) To design a fluorinated polymer simultaneously owning a down-shifted HOMO and reduced optical bandgap (Egopt). The main contents are as follows.
1. Benzene was used to extend the π-conjugation system of the polymer based on alkylthienyl-substituted benzodithiophene. Compared with thiophene, benzene is π-deficient. Fusing benzene on the polymer down-shifted HOMO and LUMO levels from -5.36 and -3.60 eV to -5.47 and -3.73 eV, respectively. The Egopt of the polymer was reduced from 1.76 to 1.74 eV, leading to a red-shifted absorption edge of 713 nm. Additionally, the polymer with extended π-conjugation system showed noticeably enhanced intermolecular interactions and a slightly improved thermal decomposition temperature. Fusing benzene on the polymer significantly improved its photovoltaic properties. The short-circuit current density (Jsc) of the best-performing photovoltaic devides was increased from 9.83 to 12.93 mA/cm2, and the optimum power conversion efficiency (PCE) was increased from 5.35% to 7.30%.
2. Benzene was used to extend the π-conjugation system of the polymer based on alkoxyphenyl-substituted benzodithiophene. Fusing benzene on the polymer down-shifted HOMO and LUMO levels from -5.23 and -3.51 eV to -5.49 and -3.78 eV, respectively. The Egopt (1.71 eV) of the polymer was nearly unchanged. The photovoltaic properties of the polymer were slightly improved by fusing benzene. The Voc of the best-performing photovoltaic devides was increased from 0.83 to 0.84 V, and the Jsc was increased from 11.33 to 12.29 mA/cm2. Consequently, the optimum PCE was increased from 6.23% to 6.57%.
3. A novel polycyclic aromatic unit dithienobenzothiadiazole (fDTBT) was designed by fusing two thiophene rings onto benzothiadiazole (BT). fDTBT has a curved configuration and indacenodithiophene (IDT) has side chains stretched out of the backbone plane. A new polymer PIDT-fDTBT comprising alternating fDTBT and IDT was designed and it was an ideal polymer to study the effects of curvature on photovoltaic properties. The HOMO level of PIDT-fDTBT was down-shifted by 0.08 eV while the LUMO was up-shifted by 0.2 eV in comparison with those of the BT-containing polymer. As a result, PIDT-fDTBT exhibited an increased Egopt of 2.03 eV. The Voc of PIDT-fDTBT-based photovoltaic devices was pronouncedly enhanced, reaching 0.90 V. However, the Jsc and PCE were decreased due to the increased bandgap.
4. We replaced the sulphur atom in fDTBT with oxygen atom and synthesized another polycyclic aromatic compound dithienobenzooxadiazole (fDTBO). Compared with fDTBT, fDTBO also has a curved configuration but with stronger electron-withdrawing ability. Two polymers utilizing fDTBO as electron-deficient unit and alkoxy-substituted benzodithiophene (BDTO) and alkylthienyl-substituted benzodithiophene (BDTT) as electron-rich units were synthesized, respectively. The Egopt were 2.00 and 1.95 eV for PBDTO-fDTBO and PBDTT-fDTBO, respectively. PBDTO-fDTBO and PBDTT-fDTBO exhibited very deep HOMO energy levels of -5.58 and -5.60 eV, respectively. As a result, both of the photovoltaic devices based on PBDTO-fDTBO and PBDTT-fDTBO realized very high Voc values of over 1 V.
5. Fluorine was firstly applied in thiadiazolo[3,4-c]pyridine (PT)-containing polymer. The HOMO and LUMO levels of the fluorinated polymer PDTPT-2TF were -5.34 and -3.89 eV, down-shifted by 0.11 and 0.15 eV , respectively, in comparison with the none-fluorinated polymer PDTPT-2T. PDTPT-2TF exhibited a narrow Egopt of 1.45 eV, 0.04 eV smaller than that of PDTPT-2T. X-ray diffraction indicated that more ordered structure was formed in the solid film of PDTPT-2TF. Incorporation of fluorine into PT-containing polymer significantly improved the photovoltaic properties. The best-performing photovoltaic devices based on PDTPT-2T only gave a maximum PCE of 2.65%, with a Voc of 0.73 V, a Jsc of 5.34 mA/cm2, and a fill factor (FF) of 67.91%. In striking contrast, the maximum PCE of the devices based on PDTPT-2TF reached 8.01%, along with a slight higher Voc of 0.74 V, a significantly enhanced Jsc of 15.52 mA/cm2, and a slight higher FF of 69.73%. This efficiency is the highest one for PT-containing polymers and it was achieved without any processing additives or post-treatments.
The findings of this dissertation indicate that: (i) Extending π-conjugation system and increasing backone curvature of polymers are two effective strategies to simultaneously extend the π-conjugation system and down-shift the HOMO energy level of the polymer; (ii) Incorporating fluorine into DTPT-2T polymer can simultaneously down-shift the HOMO energy level and reduce the Egopt. This dissertation is of great significance in perfecting the theory of organic electronics
基于有机太阳能电池中新型活性层材料和传输层材料的实验与理论研究
No full text理论计算表明，将强吸电子集团氰基（-CN）被引入聚3-己基噻吩（P3HT）的骨架可以提高有机太阳能电池光伏性能的有效方式。通过密度泛函理论（DFT）和分子动力学（MD）模拟，系统地研究了取代效应对P3HT给体聚合物分子光学及光伏性能的影响。理论模拟结果显示，通过直接将强吸电子集团-CN引入到P3HT聚合物的骨架，相对于未取代的和F原子取代的P3HT，不仅可以显著降低聚合物的HOMO能级，从而提高太阳能电池器件的开路电压（VOC），同时还可以使其吸收光谱红移并提高材料的空穴迁移率，从而提高太阳能电池器件的短路电流（JSC）和填充因子（FF）。该研究结果提供了不同吸电子取代基团对共轭聚合物光物理、电化学和光电子性质影响的深入理解，并为未来高效率有机太阳能电池的设计策略提供了有用的信息。Calculations have been made regarding the strong electron-withdrawing cyano (-CN) group, which was introduced onto the backbone of poly(3-hexylthiophene) (P3HT), as an effective way to improve the parameters essential for the photovoltaic performance of organic solar cells (OSCs). The substitution effect on the optical and photovoltaic properties of various CN-substituted P3HT are comprehensively investigated by means of density functional theory and molecular dynamics simulation. The results of theoretical modeling indicate that the direct introduction of strong electron-withdrawing group -CN onto the backbone of P3HT, can not only significantly reduce the HOMO level of polymer which leads to increased open circuit voltage (VOC) in solar cells, but also exhibit red-shifted absorption spectra and increased hole mobility, which might lead to the enhancement of the short circuit current (JSC) and the fill factor (FF) in comparison to pristine P3HT and fluorine (F)-substituted P3HT. These results provide a fundamental understanding of how different electron-withdrawing groups influence the photophysical, electrochemical, and optoelectronic properties of conjugated polymers and potentially provide useful information for better design strategy for OSCs
全固态电池材料的制备及性能研究
No full text锂离子固态电解质作为全固态电池的关键组件之一，其性能很大程度决定了电池的功率密度、循环稳定性、安全性能、高低温性能以及使用寿命。本文通过合理优化电解质材料及电解质的制备工艺来提高电解质的电化学性能及稳定性，并确立了电解质制备的最佳工艺。同时，针对中低温固体氧化物燃料电池阴极极化电阻大的问题，对阴极材料的特性及微观结构进行了优化，提高了阴极的电化学性能。
本文的主要结论如下：
1. 采用一种改良的Pechini合成方法制备了NASICON结构的Li1.3Al0.3Ti1.7(PO4)3(LATP)电解质材料。通过优化制备工艺参数，如分散剂、粉体的烧结温度、电解质片烧结温度和时间，制备出了高性能LATP电解质。电解质在303 K下的最高电导率为6.0×10-4 S/cm，高于大多数文献报道的结果，其良好的性能归因于电解质致密的结构，其致密度高达95.76%，而且该电解质具有可忽略的电子电导率，其数值仅为1.2 ×10-8 S/cm。
2. 为了抑制LATP电解质与Li负极的反应，通过一种简单廉价的干压技术在LATP电解质基体表面构筑了Li1.3Al0.3Ge1.7(PO4)3(LAGP)阻隔层，形成了LATP/LAGP双层电解质。650 °C合成的LAGP与LATP基体烧结行为匹配，制备的双层电解质表面平整、光滑、结构致密。制备的电解质具有良好的电化学性能及稳定性，室温电导率为3.4×10-4 S/cm，电子电导率数值为9.6×10-9 S/cm，在空气中长时间放置以及与Li金属接触，电化学性能均未衰减。组装了LiFePO4(LFP)电池，在0.1C电流下，电池的首次充放电容量为142.0 mAh/g和130.6 mAh/g，3次循环后，容量分别增至145.3和141.4 mAh/g。
3. 采用一种改良的溶胶凝胶法合成了一系列La0.3Sr0.7T1-xCoxO3 (LSCT, x=0.1-0.8)阴极材料，通过优化Co的掺杂量，获得了高性能的阴极材料，当x=0.8时，阴极在550 °C、600 °C、650 °C下的极化电阻数值分别为1.12、0.40和0.15 Ω cm2，活化能为1.435 eV，良好的电化学性能主要归因于电极内部氧的解离和电荷传输能力的提高。Solid state electrolyte is one of key components for all solid state lithium ion batteries, which greatly determines the power density, cycle stability, safety performance, high and low temperature performance and the life of batteries. Herein, to improve the electrochemical performance and stability of solid state electrolyte, the preparation process for electrolyte materials and electrolytes was optimized. Moreover, the optimum process was identified. Meantime, in order to reduce the polarization resistance of intermediate temperature solid oxide fuel cell, the intrinsic properties and microstructure of cathode materials were optimized, and thus the cathode performance was improved.
The main conclusions of this paper can be sumarried as follows:
1. The Li1.3Al0.3Ti1.7(PO4)3 (LATP) electrolyte materials with NASICON structure were prepared via a modified Pechini synthesis method. By optimizing the preparation process parameters, such as dispersant, calcination temperature for electrolyte powders, sintering temperature and period for electrolyte pellets, the high performance LATP electrolyte was obtained with the highest electrical conductivity of 6.0 x 10-4 S/cm at 303 K, which is comparable to those reported in references. The excellent electrochemical performance is due to the high densification of electrolyte with the relative density of 95.76%. Additionally, the electrolyte has a negligible electronic conductivity, whose value is only 1.2 x 10-8 S/cm.
2. In order to inhibit the reaction between LATP electrolyte and Li anode, a Li1.3Al0.3Ge1.7(PO4)3 (LAGP) barrier layer was constructed on the surface of LATP electrolyte substrate to form a LATP/LAGP double-layer electrolyte via a simple and inexpensive dry-pressing technique. A dense and smooth solid state electrolyte with dense structure can be obtained using the LAGP starting materials sintered at 650 °C, which is due to the good sintering match between LAGP layer and LATP substrate. The electrolyte exhibited excellent electrochemical performances and stability. Its electrical conductivity at room temperature is 3.4 x 10-4 S/cm, and the value of electronic conductivity is 9.6 x 10-9 S/cm. When the electrolyte was placed in the air for a long time or contacted with Li metal, its electrochemical properties were not attenuated. The assembled LiFePO4 (LFP) battery showed the first charge and discharge capacities of 142 mAh/g and 130.6 mAh/g. After 3 cycles, the capacities was increased to 145.3 and 141.4 mAh/g.
3. A series of perovskite-type La0.3Sr0.7T1-xCoxO3 (LSCT, x=0.1-0.8) cathode materials for solid oxide fuel cells were synthesized via a convenient modified sol-gel method. By optimizing the content of Co dopant, high perforamce cathode materials were obtained. The LSCT cathode with “x= 0.8” has the best electrochemical performance, achieving the polarization resistances of 1.12, 0.40 and 0.15 Ω cm2 at 550, 600 and 650 °C, and the activation energy of the LSCT cathode was 1.435 eV, which was attributed to the enhancement of the molecular oxygen dissocation and charge transfer process in the cathode
Low stability of the reduced state of Mycobacterium tuberculosis NrdH redoxin
No full textNrdH redoxin is the only hydrogen donor for ribonucleotide reductase in Mycobacterium tuberculosis. Several crystal structures of NrdH redoxins in the oxidized state from different species have been reported, but no structure of the reduced state has yet been reported. Using NMR spectroscopy, we found surprisingly that the reduced NrdH redoxin from M. tuberculosis is largely unfolded at a pH lower than the pKa of its first active site cysteine, and the structural basis of the low stability was analyzed. In addition, a single mutant of the NrdH redoxin suitable to determine the structure in the reduced state was obtained
Characterisation of algicidal bacterial exometabolites against the lipid-accumulating diatom Skeletonema sp.
No full textMicroalgae are of increasing interest due to their occurrence in the environment as harmful algal blooms and as a source of biomass for the production of fine and bulk chemicals. A method for the low cost disruption of algal biomass for environmental remediation or bioprocessing is desirable. Naturally-occurring algal lytic agents from bacteria could provide a cost-effective and environmentally desirable solution. A screen for algal lytic agents against a range of marine microalgae has identified two strains of algicidal bacteria isolated from the coastal region of the Western English Channel. Both strains (designated EC-1 and EC-2) showed significant algicidal activity against Skeletonema sp. and were identified as members of Alteromonas sp. and Maribacter sp. respectively. Characterisation of the two bioactivities revealed that they are small extracellular metabolites displaying thermal and acid stability. Purification of the EC-1 activity to homogeneity and initial structural analysis has identified it as a putative peptide with a mass of 1266 amu. (C) 2015 Elsevier B.V. All rights reserved
Metabolic engineering of Escherichia coli for the production of hydroxy fatty acids from glucose
No full textBackground: Hydroxy fatty acids (HFAs) are valuable chemicals for a broad variety of applications. However, commercial production of HFAs has not been established so far due to the lack of low cost routes for their synthesis. Although the microbial transformation pathway of HFAs was extensively studied decades ago, these attempts mainly focused on converting fatty acids or vegetable oils to their hydroxyl counterparts. The use of a wider range of feedstocks to produce HFAs would reduce the dependence on oil crops and be expected to cut down the manufacturing cost
Engineering Escherichia coli for high-yield geraniol production with biotransformation of geranyl acetate to geraniol under fed-batch culture
No full textBackground: Geraniol is an acyclic monoterpene alcohol, which exhibits good prospect as a gasoline alternative. Geraniol is naturally encountered in plants at low concentrations and an attractive target for microbial engineering. Geraniol has been heterologously produced in Escherichia coli, but the low titer hinders its industrial applications. Moreover, bioconversion of geraniol by E. coli remains largely unknown
Recombinant Collagen Engineered to Bind to Discoidin Domain Receptor Functions as a Receptor Inhibitor
No full textA bacterial collagen-like protein Scl2 has been developed as a recombinant collagen model system to host human collagen ligand-binding sequences, with the goal of generating biomaterials with selective collagen bioactivities. Defined binding sites in human collagen for integrins, fibronectin, heparin, and MMP-1 have been introduced into the triple-helical domain of the bacterial collagen and led to the expected biological activities. The modular insertion of activities is extended here to the discoidin domain receptors (DDRs), which are collagen-activated receptor tyrosine kinases. Insertion of the DDR-binding sequence from human collagen III into bacterial collagen led to specific receptor binding. However, even at the highest testable concentrations, the construct was unable to stimulate DDR autophosphorylation. The recombinant collagen expressed in Escherichia coli does not contain hydroxyproline (Hyp), and complementary synthetic peptide studies showed that replacement of Hyp by Pro at the critical Gly-Val-Met-Gly-Phe-Hyp position decreased the DDR-binding affinity and consequently required a higher concentration for the induction of receptor activation. The ability of the recombinant bacterial collagen to bind the DDRs without inducing kinase activation suggested it could interfere with the interactions between animal collagen and the DDRs, and such an inhibitory role was confirmed in vitro and with a cell migration assay. This study illustrates that recombinant collagen can complement synthetic peptides in investigating structure-activity relationships, and this system has the potential for the introduction or inhibition of specific biological activities
Ultrafast structural flattening motion in photoinduced excited state dynamics of a bis(diimine) copper(I) complex
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The ultrafast photoinduced structural change dynamics of a prototypical Cu(I) complex, namely, [Cu(dmp)(2)](+) (dmp = 2,9-dimethyl-1,10-phenanthroline), is investigated based on the theoretical analysis of static and dynamical calculations at the all-atomic level. This work mainly focuses on the intriguing structural flattening features of [Cu(dmp)(2)](+) occurring in the metal-to-ligand charge transfer singlet excited state ((MLCT)-M-1) on the sub-picosecond timescale. Our estimated time constant (similar to 675 fs) of this "flattening'' motion is in good agreement with recent experimental values. The full-dimensional excited-state nonadiabatic dynamic simulation provides a direct view of the ultrafast photoinduced events of [Cu(dmp)(2)](+), especially, the structural flattening mechanism on the S-1 state. Several molecular motions (such as Cu-N stretching, the motion of the substituted groups etc.) with distinguishable time scales are involved in the flattening dynamics. The Fourier transformation of the time-dependent oscillation of the Cu-N bond and the N-Cu-N bond angle provides consistent conclusions with the experimental spectrum analysis. These dynamics details imply that various nuclear motions are strongly coupled in the high-dimensional excited-state potential energy surface responsible for the geometrical evolution of [Cu(dmp)(2)](+). This work provides us a unique fundamental understanding of the ultrafast photoinduced excited-state nonadiabatic process of Cu(I) complexes and their derivatives, which should have potential impacts on various research fields, such as photo-catalysts, dye-sensitized solar cells (DSSCs), and organic light emitting diodes (OLEDs).</p
Microbial production of amino acid-modified spider dragline silk protein with intensively improved mechanical properties
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Spider dragline silk is a remarkably strong fiber with impressive mechanical properties, which were thought to result from the specific structures of the underlying proteins and their molecular size. In this study, silk protein 11R26 from the dragline silk protein of Nephila clavipes was used to analyze the potential effects of the special amino acids on the function of 11R26. Three protein derivatives, ZF4, ZF5, and ZF6, were obtained by site-directed mutagenesis, based on the sequence of 11R26, and among these derivatives, serine was replaced with cysteine, isoleucine, and arginine, respectively. After these were expressed and purified, the mechanical performance of the fibers derived from the four proteins was tested. Both hardness and average elastic modulus of ZF4 fiber increased 2.2 times compared with those of 11R26. The number of disulfide bonds in ZF4 protein was 4.67 times that of 11R26, which implied that disulfide bonds outside the poly-Ala region affect the mechanical properties of spider silk more efficiently. The results indicated that the mechanical performances of spider silk proteins with small molecular size can be enhanced by modification of the amino acids residues. Our research not only has shown the feasibility of large-scale production of spider silk proteins but also provides valuable information for protein rational design.</p