Hybrid bulk heterojunction solar cells from a blend of poly(3-hexylthiophene) and TiO2 nanotubes

Hybrid bulk heterojunction solar cells based on blend of poly(3-hexylthiophene) (P3HT) and TiO2 nanotubes or dye(N719) modified TiO2 nanotubes were processed from solution and characterized to research the nature of organic/inorganic hybrid materials. Compared with the pristine polymer P3HT and TiO2 nanoparticles/P3HT solar cells, the TiO2 nanotubes/P3HT hybrid solar cells show obvious performance improvement, due to the formation of the bulk heterojunction and charge transport improvement. A further improvement in the device performance can be achieved by modifying TiO2 nanotube surface with a standard dye N719 which can play a role in the improvement of both the light absorption and charge dissociation. Compared with the non-modified TiO2 nanotubes solar cells, the modified ones have better power conversion efficiency under 100 mW/cm(2) illumination with 500W Xenon lamp. (C) 2008 Elsevier B. V. All rights reserved.

立构规整型聚(3-烷基噻吩)的结晶形态与结构研究

立构规整聚(3-烷基噻吩)是具有高功能的聚合物光电材料，被广泛用于有机光电器件的制备与集成。本论文利用一种新的结晶方法，即溶剂辅助结晶，得到了梳状刚性链高分子RR-P3BT毫米级的新晶体及其晶胞参数。同时，还得到了RR-P3BT的分子链在这种新晶体中的堆砌方式。首次直接证明了刚性链高分子RR-P3BT的晶体生长方式是层状生长。又采用溶液等温结晶的方法，得到了RR-P3BT的多种晶体。包括Whisker晶体，平行四边形片晶，小长方形片晶和棒状单晶。并得出了这些晶体的晶胞参数和分子链的堆砌方式。通过溶液等温结晶也得到了RR-P3HT的多种晶体。包括Whisker晶体，长方形片晶，平行四边形片晶和六边形片晶。并得出这些晶体的晶胞参数和分子链的堆砌方式。

微图案化新方法及在有机光电器件加工中的应用

有机半导体材料正以其光电性能优异、生产成本低廉，加工工艺简单，选材范围宽广，性质调节方便，易于制成大面积器件，与柔性基底结合性好对器件适度弯曲或扭曲而光电性能无明显改变等显著优点，吸引了世界范围内的目光。新的加工方法在有机微电子器件产生、发展和应用中发挥着技术推动力的作用。而从传统的硅基材料为基础的无机微电子中发展起来的光刻工艺，由于制作成本非常昂贵，工艺十分复杂，对环境要求苛刻，不适宜大面积生产，很难制作尺寸小于100nm的图形，而且大多数有机材料的光电性能在光刻胶、显影液等溶液中会大幅的下降，所以不适于有机器件的加工，因此目前开发适合有机材料的廉价大面积加工方法成为研究的焦点。本论文在软刻蚀技术基础上，以机械瓤附力或毛细力为图案化驱动力提出了多种有机电子器件加工方法，并取得了初步的结果。主要有三种方法：金属传递打印、热剥离、冰模板方法。（1）利用聚合物粘弹性随温度和饱和溶剂处理时间变化的规律，通过调控金属薄膜和模板及金属薄膜和聚合物薄膜之间界面相互作用力，发展出以机械粘附力作为图案化驱动力的金属传递打印（MTP）方法。它可以适用于多种材料例如Au、AI等金属和PS、PMMA等多种聚合物。这种方法的分辨率目前在5协m左右。与其它打印技术相比MTP的一个显著的优点是它可以形成多层结构，这种结构在微电子电路（如欧姆接触等方面）中有着巨大的潜在应用价值。为展示金属传递打印在有机电子器件加工中的应用，我们将MTP用于有机场效应晶体管（OFETs）的加工，并在-3cm*3cm的Si片上形成大面积晶体管器件。这些器件的场效应迁移率-0.0193士0.0038cm2V-1s-1。（2）发展了一种用环氧树脂模板为模板图案化的方法一热剥离（Hotlift-off）。它是一种利用机械薪附力为图案化驱动力的方法，所以适用材料范围非常广泛，既可以加工有机电子器件的有源部分一有机半导体材料，也可以加工有机电子器件的金属电极部分，是一种多功能的方法。我们将热剥离用于有机晶体管和有机发光二极机管的加工。这些器件的性能与用其它方法加工的器件性能相当。（3）我们用冰为模板实现了聚合物的图案化，因为大多数聚合物溶液对冰模板不会产生溶解、溶胀作用，所以这种方法适用于许多聚合物材料如P3HT、PvK和PMMA等。这种方法与其它使用PDMS、硅片或金属为模板的方法相比最突出的优点是冰模板非常容易被除去。所以使用冰模板方法可以加工出多种别的方法无法胜任的聚合物结构如多元聚合物结构，自由无支撑的聚合物结构，聚合物微沟道。以上这些图案化技术具有快速大面积图案化、可在开放的空气环境中操作的优点，为发展适宜于未来塑性电子器件卷帘式（reel to reel）的加工过程提供新思路，促进了塑性电子学的发展。

Improving performance of polymer photovoltaic devices using an annealing-free approach via construction of ordered aggregates in solution

Low crystalline order has been proved to be one of the main hindrances for achieving high performance devices based on thin films composed of crystallizable polymer. In this work, we use a facile method to substantially improve crystallinity of poly(3-hexylthiophene) (P3HT) in its pure or composite film via the construction of ordered precursors in the solution used for thin film deposition. These improvements have been confirmed by bright-field transmission electron micrography, electron diffraction, UV-Vis absorption and wide-angle X-ray diffraction.

Effects of thermal annealing on polymer photovoltaic cells with buffer layers and in situ formation of interfacial layer for enhancing power conversion efficiency

We have investigated the effects of thermal annealing before and after cathode deposition on poly(3-hexylthiophene)(P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend photovoltaic cells with different cathode buffer layers. The introduction of cathode buffer layer such as lithium fluoride (LiF) and calcium oxide (CaO) in pre-annealing cells can increase the open-circuit voltage (V-oc) and the power conversion efficiency (PCE). Post thermal annealing after cathode deposition further enhanced the PCE of the cells with LiF/Al cathode.

Synthesis and characterization of phenylene-thiophene all-conjugated diblock copolymers

Grignard metathesis (GRIM) polymerization for all-conjugated diblock copolymers comprising poly (2,5-dihexyloxy-1,4-phenylene) (PPP) and poly(3-hexylthiophene) (P3HT) blocks were systematically studied with LiCl as additive and 1,2-bis (diphenylphosphino) ethane nickel dichloride (Ni(dppe)Cl-2) or 1,3-bis(diphenylphosphino) propane nickel dichloride (Ni(dppp)Cl-2) as catalyst. It was found that the addition order of the monomers was crucial for the success of copolymerization. With the monomer addition in the order of phenyl and then thienyl Grignard reagents, all-conjugated PPP-b-P3HT diblock copolymers with different block ratios were successfully synthesized. In contrast, the inverted addition order only afforded a mixture containing both block copolymers and deactivated or end-capped homopolymers.

Effects of fullerene solubility on the crystallization of poly(3-hexylthiophene) and performance of photovoltaic devices

The substantial crystallization suppression of poly(3-hexylthiophene) (P3HT) in the untreated P3HT:C60 composite film prepared from o-dichlorobenzene (ODCB) solution has been revealed. Besides, the effective conjugation length of P3HT in this composite has been nearly maintained to that in the solution. The different crystallization behaviors of P3HT in its composites with C60 and [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) are mainly attributed to the relative solubility of C60 and PCBM with respect to P3HT in ODCB. The solution to overcome this disadvantage of chain conformation and crystallinity of P3HT in the composite with C60 is thus proposed and finalized by resorting to the addition of low volatile solvent with much higher solubility of C60 than P3HT into the main solvent used, so as P3HT can crystallize before C60 forms crystallites in the solution. The feasibility of this approach has been proven by the improved efficiency of devices based on composites of P3HT and the low cost C60 without resorting to post-treatments.

Solvent Vapor-Induced Self Assembly and its Influence on Optoelectronic Conversion of Poly(3-hexylthiophene): Methanofullerene Bulk Heterojunction Photovoltaic Cells

Nanoscale-phase separation of electron donor/acceptor blends is crucial for efficient charge generation and collection in Polymer bulk heterojunction photovoltaic cells. We investigated solvent vapor annealing effect of poly(3-hexylthiophene) (P3HT)/methanofullerene (PCBM) blend oil its morphology and optoelectronic properties. The organic solvents of choice for the treatment have a major effect oil the morphology of P3HT/PCBM blend and the device performance. Ultraviolet-visible absorption spectro,;copy shows that specific solvent vapor annealing can induce P3HT self-assembling to form well-ordered structure; and hence, file absorption in the red region and the hole transport are enhanced. The solvent that has a poor Solubility to PCBM Would cause large PCBM Clusters and result in a rough blend film. By combining an appropriate solvent vapor treatment and post-thermal annealing of the devices, the power conversion efficiency is enhanced.

Effect of Poly (3-hexylthiophene) Nanofibrils on Charge Separation and Transport in Polymer Bulk Heterojunction Photovoltaic Cells

Crystalline poly (3-hexylthiophene) (P3HT) nanofibrils are introduced into the P3HT: [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) composite films via P3HT preaggregation in solution by adding a small amount of acetone, and the correlation of P3HT nanofibrils and the optoelectronic properties of P3HT:PCBM bulk heterojunction photovoltaic cells is investigated. It is found that the optical absorption and the hole transport or the resulted P3HT:PCBM composite films increase with the increase of the amount of P3HT nanofibrils due to the increased P3HT crystallinity and highly interconnected nanofibrillar P3HT networks. However, it is also found that high contents of crystalline P3HT nanofibrils may restrain PCBM molecules from demixing with the P3HT component that forms electron traps in the active layer. and hence reduce the charge collection efficiency. Small contents of P3HT nanofibrils not only improve the demixing between P3HT and PCBM components, but also enhance the hole transport via crystalline P3HT nanofibrillar networks, resulting in efficient charge collection.

Solvent-vapor treatment induced performance enhancement of poly(3-hexylthiophene): methanofullerene bulk-heterojunction photovoltaic cells

The authors report enhanced poly(3-hexylthiophene) (P3HT):methanofullerene (PCBM) bulk-heterojunction photovoltaic cells via 1,2-dichlorobenzene (DCB) vapor treatment and thermal annealing. DCB vapor treatment can induce P3HT self-organizing into ordered structure leading to enhanced absorption and high hole mobility. Further annealing the device at a high temperature, PCBM molecules begin to diffuse into aggregates and together with the ordered P3HT phase form bicontinuous pathways in the entire layer for efficient charge separation and transport. Compared to the control device that is merely annealed, optical absorption, short-circuit current, and power conversion efficiency are increased for the DCB vapor-treated cell.

Enhanced electrical conductivity of highly crystalline polythiophene/insulating-polymer composite

Poly(3-butylthiophene) (P3BT)/insulating-polymer composites with high electrical conductivity have been prepared directly from the solution. These composites exhibit much higher conductivity compared to pure P3BT with the same preparation method provided that P3BT content is higher than 10 wt %. Morphological studies on both the pure P3BT and the composites with insulating polymer show that P3BT highly crystallizes and develops into whisker-like crystals. These nanowires are homogeneously distributed within the insulating polymer matrix and form conductive networks, which provide both extremely large interface area between conjugated polymer and insulating polymer matrix and highly efficient conductive channels through out the whole composite. In contrast, the conductivity enhancement of P3HT/PS composite is not so obvious and drops down immediately with increased PS content due mainly to the absence of highly crystalline whisker-like crystals and much larger scale phase separation between the components. The results presented here could further illuminate the origin of conductivity formation in organic semiconducting composites and promote applications of these polymer semiconductor/insulator composites in the fields of organic (opto-)electronics, electromagnetic shielding, and antistatic materials.

Direct micropatterning of polymer materials by ice mold

Micropatterning of functional polymer materials by micromolding in capillaries (MIMIC) with ice mold is reported in this paper. Ice mold was selected due to its thaw or sublimation. Thus, the mold can be easily removed. Furthermore, the polymer solution did not react with, swell, or adhere to the ice mold, so the method is suitable for many kinds of materials (such as P3HT, PMMA Alq(3)/PVK, PEDOT: PSS, PS, P2VP, etc.). Freestanding polymer microstructures, binary polymer pattern, and microchannels have been fabricated by the use of ice mold freely.

Design de nouvelles fonctionnelles en théorie de la fonctionnelle de la densité et conception de polymères pour application à la photovoltaïque organique

La présente thèse porte sur les calculs utilisant la théorie de la fonctionnelle de la densité (DFT) pour simuler des systèmes dans lesquels les effets à longue portée sont importants. Une emphase particulière est mise sur les calculs des énergies d’excitations, tout particulièrement dans le cadre des applications photovoltaïques. Cette thèse aborde ces calculs sous deux angles. Tout d’abord, des outils DFT déjà bien établis seront utilisés pour simuler des systèmes d’intérêt expérimental. Par la suite, la théorie sous-jacente à la DFT sera explorée, ses limites seront identifiées et de nouveaux développements théoriques remédiant à ceux-ci seront proposés. Ainsi, dans la première partie de cette thèse, des calculs numériques utilisant la DFT et la théorie de la fonctionnelle de la densité dépendante du temps (TDDFT) telles qu’implémentées dans le logiciel Gaussian [1] sont faits avec des fonctionnelles courantes sur des molécules et des polymères d’intérêt expérimental. En particulier, le projet présenté dans le chapitre 2 explore l’utilisation de chaînes latérales pour optimiser les propriétés électroniques de polymères déjà couramment utilisés en photovoltaïque organique. Les résultats obtenus montrent qu’un choix judicieux de chaînes latérales permet de contrôler les propriétés électroniques de ces polymères et d’augmenter l’efficacité des cellules photovoltaïques les utilisant. Par la suite, le projet présenté dans le chapitre 3 utilise la TDDFT pour explorer les propriétés optiques de deux polymères, le poly-3-hexyl-thiophène (P3HT) et le poly-3-hexyl- sélénophène (P3HS), ainsi que leur mélange, dans le but d’appuyer les observations expérimentales indiquant la formation d’exciplexe dans ces derniers. Les calculs numériques effectués dans la première partie de cette thèse permettent de tirer plusieurs conclusions intéressantes, mais mettent également en évidence certaines limites de la DFT et de la TDDFT pour le traitement des états excités, dues au traitement approximatif de l’interaction coulombienne à longue portée. Ainsi, la deuxième partie de cette thèse revient aux fondements théoriques de la DFT. Plus précisément, dans le chapitre 4, une série de fonctionnelles modélisant plus précisément l’interaction coulombienne à longue portée grâce à une approche non-locale est élaborée. Ces fonctionnelles sont basées sur la WDA (weighted density approximation), qui est modifiée afin d’imposer plusieurs conditions exactes qui devraient être satisfaites par le trou d’échange. Ces fonctionnelles sont ensuite implémentées dans le logiciel Gaussian [1] et leurs performances sont évaluées grâce à des tests effectués sur une série de molécules et d’atomes. Les résultats obtenus indiquent que plusieurs de ces fonctionnelles donnent de meilleurs résultats que la WDA. De plus, ils permettrent de discuter de l’importance relative de satisfaire chacune des conditions exactes.

Structure and thickness optimization of active layer in nanoscale organic solar cells

 This paper presents the development of a two-dimensional model of multilayer bulk heterojunction organic nanoscale solar cells, consisting of the thickness of active layer and morphology of the device. The proposed model is utilized to optimize the device parameters in order to achieve the best performance using particle swarm optimization algorithm. The organic solar cells under research are from poly (3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester type which are modelled to be investigated for performance enhancement. A three-dimensional fitness function is proposed involving domain size and active layer thickness as variables. The best results out of 20 runs of optimization show that the optimized value for domain size is 17 nm, while the short-circuit current vs. voltage characteristic shows a very good agreement with the experimental results obtained by previous researchers. © 2014 Springer Science+Business Media New York

Electrical characterization of poly(amide-imide) for application in organic field effect devices

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)