聚合物:富勒烯薄膜光伏电池的反常高温热稳定性研究

聚合物太阳能电池光电转换效率已接近商业化要求,但稳定性差却成为其实用化瓶颈因素.高温暴晒是聚合物太阳能电池实用化必须面临的环境,因此提高聚合物太阳能电池的热稳定性至关重要.本文以典型的Poly(3-hexylthiophene-2,5-diyl(P3HT):[6,6]-Phenyl-C61-butyric acid methyl ester(PC61BM)基聚合物太阳能电池为研究模型,考察其在不同加热温度下(50~110℃)持续工作时的器件效率变化行为,结果发现电池在高温下表现出一种非常规的性能衰减再回升的行为,具体表现为高温下电池首先表现指数式急速衰减(20%~25%),随后发生反常的性能快速恢复至接近初始效率,之后电池保持超长的高温稳定性.光学显微镜和激光光束诱导电流成像结果证明,顶电极覆盖可以有效抑制活性层中PC61BM的聚集结晶,因而电池的反常热诱导稳定性提升与PC61BM的大量聚集结晶无关.活性层薄膜的紫外可见吸收光谱和器件外量子效率的表征结果证明,持续高温加热没有促进PC61BM二聚体的形成,反而有利于PC61BM二聚体的解离.综合实验分析结果,推测PC61BM在光照下的快速二聚反应及其高温解离是导致电池表现出反常热稳定性提升行为的主要原因.实验结果揭示了初期制备的聚合物太阳能电池实际处于一种亚稳态,对器件进行短暂的前期热退火有利于稳定活性层结构,消除亚稳态,有效提升器件稳定性.本研究工作不仅对富勒烯基聚合物太阳能电池的热诱导反常稳定性提升机理机制给出了解释,而且提供了一种提高聚合物太阳能电池稳定性的新策略.     

Large open-circuit voltage polymer solar cells by poly(3-hexylthiophene) with multi-adducts fullerenes

Polymer solar cells (PSCs) made by poly(3-hexylthiophene) (P3HT) with multi-adducts fullerenes, [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), PC61BM-bisadduct (bisPC61BM) and PC61BM-trisadduct (trisPC61BM), were reported. Electrochemistry studies indicated that PC61BM, bisPC61BM and trisPC61BM had step-up distributional lowest unoccupied molecular orbital (LUMO) energy. PSCs made by P3HT with above PC61BMs show a trend of enlarged open-circuit voltages, which is in good agreement with the energy difference between the LUMO of PC61BMs and the HOMO of P3HT. On the contrary, reduced short-circuit currents (Jsc) were observed. The investigation of photo responsibility, dynamics analysis based on photo-induced absorption of composite films, P3HT:PC61BMs and n-channel thin film field-effect transistors of PC61BMs suggested that the short polaron lifetimes and low carrier mobilities were response for reduced Jsc. All these results demonstrated that it was important to develop an electron acceptor which has both high carrier mobility, and good compatibility with the electron donor conjugated polymer for approaching high performance PSCs.     

共轭聚合物薄膜中光生载流子的产生及输运机制

对共轭聚合物光生载流子的产生机制进行了初步探讨,分析了由最初产生的电子 空穴对经过晶格驰豫之后形成极化子 激子的热离化过程,认为同一链上的激子会迅速复合,只有链间激子对光电流作出贡献.研究了共轭聚合物中载流子的输运机制,导出了共聚物的电导率公式,其计算值与实验结果符合,我们认为是极化子的链间跃迁实现了整个共聚物的电导和光致发光,较好地解释了实验事实.     

Gemini表面活性剂对疏水缔合聚丙烯酰胺界面吸附膜扩张流变性质的影响

采用小幅低频振荡和界面张力弛豫技术, 考察了疏水缔合水溶性聚丙烯酰胺(HMPAM)在正癸烷-水界面上的扩张黏弹性质, 研究了不对称Gemini表面活性剂C₁₂COONa-p-C₉SO₃Na对其界面扩张性质的影响. 研究发现, 疏水链段的存在, 使HMPAM在界面层中具有较快的弛豫过程, 扩张弹性显示出明显的频率依赖性. 表面活性剂分子可以通过疏水相互作用与聚合物的疏水嵌段在界面上形成类似于混合胶束的特殊聚集体. 表面活性剂分子与界面聚集体之间存在快速交换过程, 可以大大降低聚合物的扩张弹性. 同时, 聚合物分子链能够削弱表面活性剂分子长烷基链之间的强相互作用, 导致混合吸附膜的扩张弹性远低于单独表面活性剂吸附膜.     

以C_(70)衍生物为电子受体的高效聚合物固体薄膜太阳能电池

以PC[70]BM(phenyl C71-butyric acid methyl ester)取代PC[60]BM(phenyl C61-butyric acid methyl ester)作为电子受体材料,以MEH-PPV(poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene])为电子给体材料,制成了本体异质结(bulk heterojunction,BHJ)聚合物太阳能电池.MEH-PPV/PC[70]BM器件在AM1.5G(80 mW/cm2)模拟太阳光的光照条件下得到了3.42%的能量转换效率,短路电流值达到了6.07 mA/cm2,开路电压0.85 V,填充因子为53%.通过紫外可见吸收光谱和外量子效率的研究,发现PC[70]BM作为电子受体,对扩大光谱的吸收范围和增加活性层的吸收系数有明显的作用.同时比较了不同溶剂对该体系器件性能的影响.通过原子力显微镜(AFM)、光暗导I-V曲线等研究,分析了1,2-二氯苯有利于给体相和受体相的微相分离和载流子的传输的原因.     

两端系留纳米粒子聚合物的分子动力学模拟

两端系留纳米粒子聚合物是研究末端对聚合物链弛豫行为影响的优选分子模型.本文构建了两端系留纳米粒子聚合物模型,运用粗粒化分子动力学方法研究了两端系留纳米粒子聚合物的特征温度和弛豫行为,探讨了纳米粒子半径和聚合物链长对玻璃化转变温度、结晶温度和介电性能的影响.研究表明,聚合物两端纳米粒子的存在可延缓聚合物链的弛豫并促进结晶,使两端系留纳米粒子聚合物的玻璃化转变温度和结晶温度均增加.研究结果与相关的实验报道吻合,可加深对两端系留纳米粒子聚合物结构和性能的理解.     

非线性光学环氧聚合物的近程结构对二次谐波产生弛豫特性的影响

设计合成了三种具有不同主链化学结构的二阶非线性光学功能化环氧聚合物,并对其化学结构进行了表征,考察了聚合物近程结构对材料极化后二次谐波产生弛豫特性的影响。极化后线型聚合物链节的扭转弹性回复是二次谐波产生弛豫的主要原因,在温度处于Ｔｇ 以下或Ｔｇ 附近时玻璃化转变温度的高低决定了二次谐波产生弛豫的快慢;聚合物交联后有助于提高二次谐波产生的稳定性,但此时聚合物单个链节结构的柔顺性成为影响二次谐波产生弛豫的主要原因,刚性越大,材料将具有更稳定的二次谐波产生性能。极化聚合物的二次谐波产生弛豫过程非常复杂,需要综合考虑聚合物材料的近程和远程结构因素。     

聚合物氮化碳材料光激发过程研究进展

近年来,不含金属元素的聚合物氮化碳半导体以其独特的材料组成和电子结构特征吸引了研究人员的广泛兴趣,在诸如光催化、光致发光、光电化学等光激发相关领域具有潜在的应用前景。聚合物氮化碳光激发过程由能带结构、载流子行为、激子效应等因素所主导,对于这一过程的研究在材料性能的优化、应用领域的拓展以及应用机制的理解等方面具有重要意义。围绕这一主题,本文综述了近年来聚合物氮化碳材料光激发过程研究中取得的最新进展,简单介绍了聚合物半导体光激发过程的研究方法,分别讨论了光激发下材料中的载流子行为和激子过程,进而总结了常用改性策略对于材料光激发过程的调控机制,此外还对材料光响应特性功能化的研究进行了概括。     

聚合物氮化碳材料光激发过程研究进展

近年来,不含金属元素的聚合物氮化碳半导体以其独特的材料组成和电子结构特征吸引了研究人员的广泛兴趣,在诸如光催化、光致发光、光电化学等光激发相关领域具有潜在的应用前景。聚合物氮化碳光激发过程由能带结构、载流子行为、激子效应等因素所主导,对于这一过程的研究在材料性能的优化、应用领域的拓展以及应用机制的理解等方面具有重要意义。围绕这一主题,本文综述了近年来聚合物氮化碳材料光激发过程研究中取得的最新进展,简单介绍了聚合物半导体光激发过程的研究方法,分别讨论了光激发下材料中的载流子行为和激子过程,进而总结了常用改性策略对于材料光激发过程的调控机制,此外还对材料光响应特性功能化的研究进行了概括。     

紫菌外周捕光天线LH2中的超快能量弛豫

主要用飞秒抽运-探测技术观察了紫细菌Rb. sphaeroides 601外周捕光天线LH2中细菌叶绿素(BChl)之间的能量传递过程. 在783 nm的激光激发B800情况下, 在B800到B850的能量传递之前, 存在一个约0.35 ps的分子内能量重新分布过程; 通过调节激发波长, 清楚地观察到激发态BChl分子的动力学演变过程. 结果表明基态漂白和激发态吸收存在明显的竞争, 同时在818 nm处出现一个鞍点, 说明在B800的激发态和B850的上激子态存在快速、高效的能量传递; B850分子上激子态的激发能将通过内转换向次最低激发态快速弛豫, 并导致最低激发态布局和分子构象变化.     

Theoretical and Experimental Study of Photophysical Characteristics between Poly(9,9-dioctyl°uorene) and Poly(9,9-dioctyl°uorene-co-benzothiadiazole)

The photo-physical characteristics of semiconductor polymer are systematically stud-ied through comparing poly (9,9-dioctylfluorene) (PFO) and poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). The quantum chemical calculation shows that the introduction of benzothiadiazole unit facilitates the intrachain charge transfer (ICT) and modulates the electronic transition mechanism of polymer. The transient absorption measurement exhibits that intrachain exciton relaxation is dominant in the decay of excited PFO in a monodis-perse system and intrachain exciton interaction could appear at high excitation intensity. In F8BT solution, the ICT state exists and participates in the relaxation of excited state. The relaxation processes of PFO and F8BT in the condensed phase both accelerate and show obvious exciton-exciton annihilation behavior at high excitation intensity. At the same excitation intensity, the mean lifetime of F8BT is longer than that of PFO, which may be assigned to the excellent delocalization of charge.     

含Ullazine结构基元的共轭聚合物的合成及其光电性能研究

将Ullazine结构基元引入到聚合物主链或侧链中,分别与吡咯并吡咯二酮(DPP)、2,5-双(三甲基锡)噻吩共聚得到了二元共聚物PB和三元共聚物PT,分别利用凝胶渗透色谱和热重分析表征了聚合物的分子量和热稳定性,并研究了聚合物的光物理、电化学和光伏性能.基于共聚物PB和PT作为电子给体材料的聚合物太阳能电池器件测试结果表明,二元共聚物PB由于具有较低的能级水平从而获得较高开路电压,而侧链含Ullazine结构基元的三元共聚物PT具有更宽的吸收光谱和更高的空穴迁移率,获得了更高的短路电流和能量转换效率.     

Charge trapping and storage by composite P3HT/PC60BM nanoparticles investigated by fluorescence-voltage/single particle spectroscopy

Fluorescence-voltage/single particle spectroscopy (F-V/SPS) was employed to study exciton-hole polaron interactions and interfacial charge transfer processes for pure poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) and composite P3HT/PC(60)BM NPs in functioning hole-injection devices. F-V/SPS data collected on a particle-by-particle basis reveal an apparent bistability in the fluorescence-voltage modulation curves for composite NPs of P3HT and [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM) that is absent for pure P3HT NPs. A pronounced deep trapping of free electrons photogenerated from the composite P3HT/PC(60)BM NPs at the NP/dielectric interface and hole trapping by fullerene anions in composite P3HT/PC(60)BM NPs under photoexcitation lies at the basis of this finding. The deep electron trapping effect reported here for composite conjugated polymer/fullerene NPs presents an opportunity for future application of these NPs in nanoscale memory and imaging devices.     

Effects of Replacement on the Optical Properties of Narrow Bandgap Polymers: Comparing the Difference Between Thieno[3,2-b]thiophene Units and Thiophene Units

The effects of replacement on the optical properties of diketopyrrolopyrrole(DPP)-based polymers were discussed through replacing the thieno[3,2-b]thiophene units by thiophene units.It is easy to see that the role of replacement would lead to blue shift of steady-state absorption spectrum when thieno[3,2-b]thiophene units is replaced by thiophene units.Meanwhile,the transient absorption data indicate that the role of replacement would not change the relaxation mechanism of polymer,but is able to adjust the photo-excitation relaxation rate of polymer.Their intensity-dependent dynamic curves show that the exciton-exciton annihilation(EEA)would participate in the relaxation process when the polymer is in the aggregation.Through comparing the EEA data between the polymers,it is found that the role of replacement would change the spatial distribution of exciton.     

Quantifying the efficiency of förster‐assisted optical gain in semiconducting polymer blends by excitation wavelength selective amplified spontaneous emission

We study the correlation between Förster resonance energy transfer (FRET) and optical gain properties in conjugated polymer blends based on regioregular poly(3‐hexylthiophene) (P3HT) and poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT). First, FRET dynamics are investigated with femtosecond transient absorption spectroscopy observing a sub‐picosecond energy transfer from F8BT to P3HT (550 fs) at medium doping levels (40% wt P3HT in F8BT). Amplified spontaneous emission (ASE) is then characterized in blends upon exciting predominantly the host and guest polymers, respectively. The corresponding density of absorbed photons at threshold conditions is compared upon host or guest photoexcitation as a method to quantitatively determine the FRET‐assisted ASE efficiencies. We observe a reduction in ASE efficiency upon host photoexcitation of 20%, in the best case, respect to guest photoexcitation. Our results confirm that even in strongly coupled host:guest mixtures delayed exciton population by energy transfer is subtle to losses ascribed to exciton–exciton annihilation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2311–2317.     

Time‐resolved spectroscopy study of donor–acceptor‐type copolymers in a monodisperse system: The effect of ratio between the acceptor and the donor

The photoexcitation processes of two donor–acceptor‐type copolymers PCFBT with different ratios between the donor and the acceptor ( PCFBT_0.5 and PCFBT_0.1 ) in the solution system are systematically studied. If the number of the donor is equal to that of the acceptor in one repeat unit (such as PCFBT_0.5 ), intrachain charge transfer (ICT) can occur and participate in the relaxation of the excited state after photoexcitation. When the number of donors is much larger than that of acceptors (such as PCFBT_0.1 ) in one repeat unit, the ICT character can disappear, and the localized exciton decay process is dominant in the relaxation of the copolymer, which also involves an excitation intensity‐independent vibrational thermal relaxation process at the initial time. The results further the understanding of the basic structure‐property relationship. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 992–996     

Ultrafast dynamical localization of photoexcited states in conformationally disordered poly(p-phenylenevinylene)

We consider two types of ultrafast dynamical localization of photoexcited states in conformationally disordered poly(p-phenylenevinylene). First, we discuss nonadiabatic interconversion from higher energy extended exciton states to lower energy more localized local exciton ground states. Second, we calculate the dynamics of local exciton ground states on their Born-Oppenheimer potential energy surfaces. We show that within the first C-C bond oscillation following photoexcitation (～35 fs) the exciton becomes self-trapped and localized over approximately eight monomers. This process is associated with a Calderia-Leggett type loss of phase coherence owing to the coupling of the polymer to a dissipative environment. Subsequent torsional relaxation (on a time scale of approximately picoseconds) has little effect on the localization. We conclude from this that the initial torsional disorder determines the spatial distribution and localization length of vertical excitations but that electron-phonon coupling is largely responsible for the localization length of self-trapped excitons. We next consider the effect of dynamical localization on fluorescence depolarization. We show that exciting higher energy states causes a larger fluorescence depolarization, because these states have a larger initial delocalization. Using the observation that fluorescence depolarization is a function of excitation wavelength and polymer conformation, we show how the models of exciton localization discussed here can be experimentally investigated.