Download or read book Nanoscale Investigation and Control of the Interfacial Properties of Organic Solar Cells and Organic Thin Film Transistors written by Mahdieh Aghamohammadi and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nanoscale Investigation and Control of the Interfacial Properties of Organic Solar Cells and Organic Thin film Transistors written by Mahdieh Aghamohammadi and published by . This book was released on 2016 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: Las propiedades de las películas de semiconductores orgánicas y, en particular, de las interfases involucradas, son uno de los aspectos más prominentes en relación con la eficiencia de los dispositivos orgánicos. La interfase formada entre dos materiales orgánicos puede influenciar las propiedades electrónicas y ópticas de los dispositivos de diferentes manteras: por los mecanismos de crecimiento, la morfología, la densidad de defectos y la estructura electrónica. El impacto de la orientación molecular en interfases de materiales orgánicos es una de las cuestiones menos entendidas y menos investigadas en relación con la eficiencia de células solares orgánicas. Mediante el uso de microscopia de sonda cercana (SPM) y fotoluminiscencia, se ha demostrado en esta tesis una correlación clara entre la orientación molecular en la interfase de DIP (donor)/PTCDI-C8 (aceptor) y la formación de un estado de transferencia de carga para aquellas heteroestructuras en las que el solape de los orbitales p en moléculas adyacentes es favorecido. Otro tipo de interfase de materiales orgánicos de gran relevancia se encuentra en los transistores orgánicos de película delgada (TFTs), en el que el dieléctrico es funcionalizado con películas orgánicas autoensambladas (SAMs). El uso de SAMs es una tecnología muy prometedora en la manufacturación de transistores orgánicos para conseguir voltajes de operación deseados dado que el voltaje umbral de operación puede ser modulado mediante la elección de las SAMs. El origen físico de este fenómeno ha sido muy debatido en la literatura y permanece una cuestión abierta. Microscopia de sonda Kelvin ha sido empleada como herramienta para explorar las propiedades electrónicas de la interfase entre DNTT (semiconductor orgánico) y dos SAMs con cadenas alquílica terminadas en grupos metil o metil fluorinados. Dicho estudio en correlación con la operación de los TFTs con DNTT ha revelado que el voltaje umbral depende de la capacitancia del dieléctrico solamente para la SAM fluorinada y se ha determinado que se debe a la interacción electrónica en la interfase entre DNTT y los grupos F de la SAM. En conjunto, los estudios realizados en esta tesis combinan una serie de métodos sistemáticos y técnicas complementarias que han permitido abordar el efecto de procesos electrónicos en interfases de relevancia en células solares y TFTs. Los resultados de esta tesis ponen de manifiesto la importancia del control de las propiedades estructurales y electrónicas de las interfases de materiales orgánicos como paso necesario para mejorar la eficiencia de dispositivos.

Download or read book High Performance Thin Film Solar Cells Via Nanoscale Interface written by Yao-Tsung Hsieh and published by . This book was released on 2018 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: It has been 64 years since Bell Laboratories built the first silicon solar cell in 1954. The harnessing of the almost unlimited energy from the sun for human civilization seems not an untouchable dream anymore. However, the rapid growth of the global population companied with the growing demand to enable a decent life quality causes the energy issue more challenging than ever. Nowadays silicon solar cells continue to take a leading position, not only offering potential solutions for energy demands but also stimulating the development of various photovoltaic technologies. Among them, solution processible thin film solar cells attract most attentions due to multiple advantages over traditional silicon solar cells. In this dissertation, I focus on two most promising types of them: 1) kesterite solar cells and 2) hybrid organic-inorganic perovskite solar cells. Particularly I work on the grain growth mechanism and processing techniques via nanoscale interface engineering to improve materials thin film properties and device architecture design. In Chapter 3, Cu2ZnSn(S,Se)4 was used as a model system to demonstrate the kinetic control of solid-gas reactions at nanoscale by manipulating the surface chemistry of both sol-gel nanoparticles and colloidal nanocrystals. It was identified that thiourea (commonly used as sulfur sources for metal sulfides) can transform to melamine during the film formation, and melamine would serve as surface ligands for as-formed Cu2ZnSn(S,Se)4 nanoparticles. These surface ligands can affect the solid-gas reactions during the selenization, which enable us to control film morphologies and device performance by simply adjusting the amount of surface ligands. To further enhance Cu2ZnSn(S,Se)4 device performance, a systematic investigation on alkali metal doping effect was conducted. In Chapter 4, alkali metal-containing precursors were used to study influences on Cu2ZnSn(S,Se)4 film morphology, crystallinity and electronic properties. K-doped Cu2ZnSn(S,Se)4 solar cells showed the best device performance. Due to the surface electronic inversion effect, various thickness of CdS buffer layers were tested on K-passivated Cu2ZnSn(S,Se)4 surface for further improving device efficiency. Over 8% power conversion efficiency of K-doped Cu2ZnSn(S,Se)4 solar cell with 35 nm CdS has been reached. Finally, in Chapter 5, the hybrid organic-inorganic perovskite solar cells are introduced. We demonstrated a novel tandem device employing nanoscale interface engineering of Cu(In,Ga)Se2 surface alongside a heavy-doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] hole transporting layer between the two subcells that preserves open-circuit voltage, and enhanced both fill factor and short-circuit current. As a result, we have successfully doubled the previous efficiency record for a monolithic perovskite/Cu(In,Ga)Se2 tandem solar cell to 22.43% power conversion efficiency, which is the highest record among thin film monolithic tandem photovoltaic devices. The conclusion and future outlooks of my works on kesterite and perovskites solar cells are summarized in Chapter 6.

Download or read book Relating Nanoscale Structure to Electronic Function in Organic Semiconductors Using Time resolved Spectroscopy written by Christopher Grieco and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular packing arrangements at the nanoscale level significantly contribute to the ultimate photophysical properties of organic semiconducting materials used in solar energy conversion applications. Understanding their precise structure-function relationships will provide insights that can lead to chemical and structural design rules for the next generation of organic solar cell materials. In this work, two major classes of materials were investigated: Singlet fission sensitizers and semiconducting block-copolymers. By exploiting chemical design and film processing techniques, a variety of controllable nanoscale structures could be developed and related to their subsequent photophysical properties, including triplet and charge transport. Time-resolved optical spectroscopies, including both absorption and emission techniques, were used to measure the population dynamics of excited states and charge carriers following photoexcitation of the semiconducting materials. Singlet fission, an exciton multiplication reaction that promises to boost solar cell efficiency by overcoming thermalization loss, has been characterized in several organic molecules. If the energetics are such that the excited state singlet energy is at least twice the triplet energy, then a singlet exciton may split into two triplet excitons through an intermolecular energy-sharing process. The thin film structure of a model singlet fission compound was exploited by modulating its crystallinity and controlling polymorphism. A combination of visible, near-infrared, and mid-infrared transient absorption spectroscopies were used to investigate the precise singlet fission reaction mechanism. It was determined that the reaction intermediates consist of bound triplet pairs that must physically separate in order to complete the reaction, which results in multiplied, independent triplet excitations. Triplet transfer, which is modulated by molecular packing arrangements that control orbital overlap coupling, was found to determine the efficacy of triplet pair separation. Furthermore, the formation of these independent triplets was found to occur on longer (picosecond) timescales than previously believed, indicating that any kinetically competing relaxation processes, such as internal conversion, need to be controlled. Last, it was found that the diffusion of the multiplied triplet excitons, and thus their harvestability in devices, is highly influenced by the crystallinity of the material. In particular, the presence of even a small amount of contaminant amorphous phase was determined to be detrimental to the ultimate triplet diffusion length. Future research directions are outlined, which will be used to develop further chemical and structural design rules for the next generation of singlet fission chromophores. Semiconducting block-copolymers, because of their natural tendency to self-assemble into ordered nanoscale structures, offer an appealing strategy for controlling phase segregation between the hole and electron transport materials in organic solar cells. Such phase segregation is important for both ensuring efficient conversion of the photogenerated excitons into charge carriers, and for creating percolation pathways for efficient transport of the charges to the device electrodes. Time-resolved mid-infrared spectroscopy was developed for monitoring charge recombination kinetics in a series of block-copolymer and polymer blend films possessing distinct, controlled nanoscale morphologies. In addition to explaining previous work that correlated film structure to device efficiency, it was revealed how the covalent linkage in block-copolymers can be carefully designed to prevent rapid recombination losses. Furthermore, novel solution-phase systems of block-copolymer aggregates and nanoparticles were developed for future fundamental spectroscopic work. Future studies promise to explain precisely how polymer chain organization, including intrachain and interchain interactions, governs their ultimate charge photogeneration and transport properties in solar cells.

Download or read book Study of Structure property performance Relationships for Organic Thin film Transistors and Polymeric Solar Cells written by Sheng Bi and published by . This book was released on 2016 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic electronics has great potential for fabricating low cost, flexible and large-area devices. Despite the rapid development, several main challenges of the field need to be addressed in both organic conjugated polymer and small molecules based devices, including organic thin-film transistors (OTFTs) and polymer solar cells (PSCs). This dissertation first explores two approaches to align small molecule crystals and improve surface coverage. The controlled evaporative self-assembly (CESA) method is combined with binary solvent system using small molecule SMDPPEH to control the crystal growth. By optimizing the two solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. Also, polymer additives can be added into small molecule to control crystal alignment. As a result, mobilities are at least 10 times higher than that from spin-coated film. The SMDPPEH based OTFTs exhibit a mobility of 1.6×10-2 cm2/Vs, which is the highest mobility from SMDPPEH ever reported. The donor-acceptor vertical composition profile on the performance of the P3HT/PCBM based organic bulk heterojunction solar cells was studied. In this simulation study, variety of donor-acceptor vertical configurations was investigated for both regular and inverted PSC structures. The physical mechanisms behind the diversification of open circuit voltage, short circuit current, and fill factor, and thus power conversion efficiency from various vertical configurations are explained. The effect of vertical composition profile from the study could serve as guidance for experimental optimization of organic bulk heterojunction solar cells. Also, morphology variation of ZnO electron transport layer from atomic layer deposition and sol-gel methods on the performance of organic inverted solar cells were investigated. AFM and SEM were utilized to characterize the morphology of ZnO thin films and nanorods so as to explain the efficiency difference. The final part of the work demonstrates one-step multi-layer pattern transfer to make organic solar cells on rigid and flexible substrates. A multi-layer inking and stamping, a cost-efficient, purely additive pattern transfer technique, was developed to fabricate PSCs. GLYMO is added into PEDOT:PSS hole transport layer and its effect on PSC performance and pattern transfer yield was investigated to reach overall PSC efficiency and high yield pattern transfer.

Download or read book Scanning Probe Microscopy for Energy Research written by Dawn A. Bonnell and published by World Scientific. This book was released on 2013 with total page 640 pages. Available in PDF, EPUB and Kindle. Book excerpt: Efficiency and life time of solar cells, energy and power density of the batteries, and costs of the fuel cells alike cannot be improved unless the complex electronic, optoelectronic, and ionic mechanisms underpinning operation of these materials and devices are understood on the nanometer level of individual defects. Only by probing these phenomena locally can we hope to link materials structure and functionality, thus opening pathway for predictive modeling and synthesis. While structures of these materials are now accessible on length scales from macroscopic to atomic, their functionality has remained Terra Incognitae. In this volume, we provide a summary of recent advances in scanning probe microscopy studies of local functionality of energy materials and devices ranging from photovoltaics to batteries, fuel cells, and energy harvesting systems. Recently emergent SPM modes and combined SPM-electron microscopy approaches are also discussed. Contributions by internationally renowned leaders in the field describe the frontiers in this important field.

Download or read book Scanning Probe Microscopy For Energy Research Materials Devices And Applications written by Dawn Bonnell and published by World Scientific. This book was released on 2013-03-26 with total page 640 pages. Available in PDF, EPUB and Kindle. Book excerpt: Efficiency and life time of solar cells, energy and power density of the batteries, and costs of the fuel cells alike cannot be improved unless the complex electronic, optoelectronic, and ionic mechanisms underpinning operation of these materials and devices are understood on the nanometer level of individual defects. Only by probing these phenomena locally can we hope to link materials structure and functionality, thus opening pathway for predictive modeling and synthesis. While structures of these materials are now accessible on length scales from macroscopic to atomic, their functionality has remained Terra Incognitae. In this volume, we provide a summary of recent advances in scanning probe microscopy studies of local functionality of energy materials and devices ranging from photovoltaics to batteries, fuel cells, and energy harvesting systems. Recently emergent SPM modes and combined SPM-electron microscopy approaches are also discussed. Contributions by internationally renowned leaders in the field describe the frontiers in this important field.

Download or read book Exploring Nanoscale Properties of Organic Solar Cells written by Tobias Mönch and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Interfacial and Electrode Modifications in P3HT PC61BM Based Organic Solar Cells written by Sayantan Das and published by . This book was released on 2015 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: The inexorable upsurge in the world's energy demand has steered the search for newer renewable energy sources and photovoltaics seemed to be one of the best alternatives for energy production. Among the various photovoltaic technologies that emerged, organic/polymer photovoltaics based on solution processed bulk-heterojunctions (BHJ) of semiconducting polymers has gained serious attention owing to the use of inexpensive light-weight materials, exhibiting high mechanical flexibility and compatibility with low temperature roll-to-roll manufacturing techniques on flexible substrates. The most widely studied material to date is the blend of regioregular P3HT and PC61BM used as donor and acceptor materials. The object of this study was to investigate and improve the performance/stability of the organic solar cells by use of inexpensive materials. In an attempt to enhance the efficiency of organic solar cells, we have demonstrated the use of hexamethyldisilazane (HMDS) modified indium tin oxide (ITO) electrode in bulk heterojunction solar cell structure The device studies showed a significant enhancement in the short-circuit current as well as in the shunt resistance on use of the hexamethyldisilazane (HMDS) layer. In another approach a p-type CuI hole-transport layer was utilized that could possibly replace the acidic PEDOT:PSS layer in the fabrication of high-efficiency solar cells. The device optimization was done by varying the concentration of CuI in the precursor solution which played an important role in the efficiency of the solar cell devices. Recently a substantial amount of research has been focused on identifying suitable interfacial layers in organic solar cells which has efficient charge transport properties. It was illustrated that a thin layer of silver oxide interfacial layer showed a 28% increase in power conversion efficiency in comparison to that of the control cell. The optoelectronic properties and morphological features of indium-free ZnO/Ag/MoOx electrodes was also studied. Organic solar cells on these composite electrodes revealed good optical and electrical properties, making them a promising alternative indium free and PEDOT:PSS-free organic solar cells. Lastly, inverted solar cells utilizing zinc oxide and yttrium doped zinc oxide electron transport was also created and their device properties revealed that optimum annealing conditions and yttrium doping was essential to obtain high efficiency solar cells.

Download or read book Nano Sc Ale Investigation of Structural and Electrical Properties of Self Organized Thin Films of Phthalocyanines A Progress Towards New Photovoltaic Material written by and published by . This book was released on 2008 with total page 536 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ongoing efforts to improve the efficiency of organic photovoltaic cells emphasize the significance of the architecture of molecular assemblies in thin films, at nanometer and micron length scales, to enhance both exciton diffusion and charge transport, in donor and acceptor layers. Controlled growth of molecules via self-assembly techniques presents new opportunities to develop nano-structured organic thin films for electronic devices. This thesis is focused on controlling the orientation of phthalocyanine molecular assemblies in thin films in order to demonstrate the impact of microscopic control of molecular order on electrical properties and organic solar cell device performance. The studies performed here provide insights into the self-assembling behavior, film morphology, nanoscale electrical conductivity, and photovoltaic properties of a disk-shaped peripherally substituted phthalocyanine (Pc) molecule possessing amide functional groups in the side chains. Amide functionality was integrated in the side chains of this phthalocyanine molecule with the purpose of increasing the intra-columnar interaction through formation of a hydrogen bonding network between molecules, and to guide columnar orientation in a preferred direction via specific surface-molecule interactions. It is realized that molecule-substrate interactions must dominate over molecule-molecule interactions to achieve control over the deposition of molecules in a preferred direction for organic solar cell applications. Microscopic imaging and spectroscopic studies confirm the formation of flat-lying, well ordered, layered phthalocyanine films as anticipated. The remarkable electrical conductivity of the flat-lying phthalocyanine molecules, as studied by Conducting tip Atomic Force Microscopy (C-AFM) provide the impetus for the formation of organic solar cells based on layers of these hydrogen bonding phthalocyanine molecules. The photocurrent from devices that are made with the ordered Pc molecules and disordered Pc molecules as the primary photoactive donor layer, and vacuum deposited C60 as the acceptor material, were evaluated. The results presented here demonstrate the feasibility of increasing the photogenerated current by controlling the molecular organization in the photo active layer.

Download or read book Correlating structure and function in small molecule organic solar cells by means of scanning probe and electron microscopy written by Michael Scherer and published by BoD – Books on Demand. This book was released on 2016-07-20 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this work nanoscale properties in active layers of small molecule organic solar cells are studied regarding their impact on device performance. For this, the effect of variations in stack design and process conditions is examined both electrically and with high resolution imaging techniques. Two topics are addressed: (i) the visualization of charge extraction/injection properties of solar cell contacts and (ii) the tailoring of structural properties of co-evaporated material blends for bulk heterojunction (BHJ) organic solar cells. (i) We study the impact of controlled contact manipulation on the internal electric potential distribution of fluorinated zincphtalocyanine (F4ZnPc)/fullerene (C60) organic solar cells under operating conditions. In a detailed analytical study using photoelectron spectroscopy and in-operando scanning Kelvin probe microscopy it is demonstrated that the electric field distribution of organic solar cells at the maximum power point depends in an overproportional manner on contact properties and ranges from bulk to contact dominated even for solar cells with decent device performance. (ii) The morphology of co-evaporated active layer blends depends on both substrate and substrate temperature. Here we study the morphology of F4ZnPc:C60 blends with analytical transmission electron microscopy. For all substrates used is found that co-evaporation of the materials at elevated substrate temperature (100° Cel) induces a distinct phase segregation of F4ZnPc and C60. However, only when using a C60 underlayer, as in inverted devices, also the crystallinity of the segregated C60 phase increases. There is only a slight increase in crystallinity when F4ZnPc acts as an underlayer, as typically for non-inverted devices. Solar cell characterization reveals that the crystalline C60 domains are the main driving force for enhanced free charge carrier generation and higher power conversion efficiencies. With this we could provide a novel explanation why record efficiencies of small molecule organic solar cells are realized in inverted device architecture only.

Download or read book Interfaces in Nanoscale Photovoltaics written by Sebastian Zeki Öner and published by . This book was released on 2016 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis deals with material interfaces in nanoscale photovoltaics. Interface properties between the absorbing semiconductor and other employed materials are crucial for an efficient solar cell. While the optical properties are largely unaffected by a few nanometer thin layer, the electronic properties can change tremendously: electrical passivation of surface defects or contact selectivity can turn a piece of black rock with two metal leads into a highly efficient solar cell. On the nanoscale, highly useful properties emerge compared to wafer-based or even thin-film semiconductors. Most importantly, not only directly incident but also adjacent light can be absorbed by the single nanoscale element. As a result, an array of single nanoscale structures with much empty space in between can absorb as much light as a continuous thin-film. This effect leads to largely reduced material consumption and, depending on the growth method, even to a faster growth process for a fully absorbing layer. While this property is enormously beneficial for photovoltaics, another feature creates a great challenge: by nanostructuring semiconductors, the surface-to-volume ratio becomes much larger compared to thin-film or wafer-based solar cells. Consequently, the influence of surface and interface properties on the overall performance of the nanoscale photovoltaic elements increases substantially. In this thesis, nanowires are therefore chosen as a sensitive platform to study the impact of those interface properties on the overall photovoltaic performance. Based on the findings, device designs for more efficient practical nanowire array solar cells and a highly promising manufacturing process are proposed.

Download or read book Effects of Energetic Disorder on the Optoelectronic Properties of Organic Solar Cells written by Nikolaos Felekidis and published by Linköping University Electronic Press. This book was released on 2018-09-10 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics (OPVs) is a promising low-cost and environmental-friendly technology currently achieving 12-14% power conversion efficiency. Despite the extensive focus of the research community over the last years, critical mechanisms defining the performance of OPVs are still topics of debate. While energetic disorder is known to be characteristic of organic semiconductors in general, its potential role in OPV has received surprisingly little attention. In this thesis we investigate some aspects of the relation between energetic disorder and several optoelectronic properties of OPV. Charge carrier mobility is a key parameter in characterizing the performance of organic semiconductors. Analyzing the temperature dependence of the mobility is also an oftenused method to obtain (estimates for) the energetic disorder in the HOMO and LUMO levels of an organic semiconductor material. Different formalisms to extract and analyze mobilities from space charge limited conductivity (SCLC) experiments are reviewed. Surprisingly, the Murgatroyd-Gill analytical model in combination with the Gaussian disorder model in the Boltzmann limit yields similar mobilities and energetic disorders as a more elaborate drift-diffusion model with parametrized mobility functionals. Common analysis and measurement errors are discussed. All the models are incorporated in an automated analysis freeware tool. The open circuit voltage (Voc) has attracted considerable interest as the large difference between Voc and the bandgap is the main loss mechanism in bulk heterojunction OPVs. Surprisingly, in ternary devices composed of two donors and one acceptor, the Voc is not pinned to the shallowest HOMO but demonstrates a continuous tunability between the binary extremities. We show that this phenomenon can be explained with an equilibrium model where Voc is defined as the splitting of the quasi-Fermi levels of the photo-created holes and electrons in a common density of states accounting for the stoichiometry, i.e. the ratio of the donor materials and the broadening by Gaussian disorder. Evaluating the PCE, it is found that ternary devices do not offer advantages over binary unless the fill factor (FF) is increased at intermediate compositions, as a result of improved transport/recombination upon material blending. Stressing the importance of material intermixing to improve the performance, we found that the presence of an acceptor may drastically alter the mobility and energetic disorder of the donor and vice versa. The effect of different acceptors was studied in a ternary onedonor- two-acceptors system, where the unpredictable variability with composition of the energetic disorder in the HOMO and the LUMO explained the almost linear tunability of Voc. Designing binary OPVs based on the design rule that the energetic disorder can be reduced upon material blending, as we observed, can yield a relative PCE improvement of at least 20%. CT states currently play a key role in evaluating the performance of OPVs and CTelectroluminescence (CT-EL) is assumed to stem from the recombination of thermalized electron-hole pairs. The varying width of the CT-EL peak for different material combinations is intuitively expected to reflect the energetic disorder of the effective HOMO and LUMO. We employ kinetic Monte Carlo (kMC) CT-EL simulations, using independently measured disorder parameters as input, to calculate the ground-to-ground state (0-0) transition spectrum. Including the vibronic broadening according to the Franck Condon principle, we reproduce the width and current dependence of the measured CT-EL peak for a large number of donor-acceptor combinations. The fitted dominant phonon modes compare well with the values measured using the spectral line narrowing technique. Importantly, the calculations show that CT-EL originates from a narrow, non-thermalized subset of all available CT states, which can be understood by considering the kinetic microscopic process with which electron-hole pairs meet and recombine. Despite electron-hole pairs being strongly bound in organic materials, the charge separation process following photo-excitation is found to be extremely efficient and independent of the excitation energy. However, at low photon energies where the charges are excited deep in the tail of the DOS, it is intuitively expected for the extraction yield to be quenched. Internal Quantum Efficiency (IQE) experiments for different material systems show both inefficient and efficient charge dissociation for excitation close to the CT energy. This finding is explained by kinetic Monte Carlo simulations accounting for a varying degree of e-h delocalization, where strongly bound localized CT pairs (< 2nm distance) are doomed to recombine at low excitation energies while extended delocalization over 3-5nm yields an increased and energy-independent IQE. Using a single material parameter set, the experimental CT electroluminescence and absorption spectra are reproduced by the same kMC model by accounting for the vibronic progression of the calculated 0-0 transition. In contrast to CT-EL, CT-absorption probes the complete CT manifold. Charge transport in organic solar cells is currently modelled as either an equilibrium or a non-equilibrium process. The former is described by drift-diffusion (DD) equations, which can be calculated quickly but assume local thermal equilibrium of the charge carriers with the lattice. The latter is described by kMC models, that are time-consuming but treat the charge carriers individually and can probe all relevant time and energy scales. A hybrid model that makes use of the multiple trap and release (MTR) concept in combination with the DD equations is shown to describe both steady-state space charge limited conductivity experiments and non-equilibrium time-resolved transport experiments using a single parameter set. For the investigated simulations, the DD-MTR model is in good agreement with kMC and ~10 times faster. Steady-state mobilities from DD equations have been argued to be exclusively relevant for operating OPVs while charge carrier thermalization and non-equilibrium time-dependent mobilities (although acknowledged) can be disregarded. This conclusion, based on transient photocurrent experiments with ?s time resolution, is not complete. We show that non-equilibrium kMC simulations can describe the extraction of charge carriers from subps to 100 ?s timescales with a single parameter set. The majority of the fast charge carriers, mostly non-thermalized electrons, are extracted at time scales below the resolution of the experiment. In other words, the experiment resolves only the slower fraction of the charges, predominantly holes.

Download or read book Molecular Structures and Device Properties of Organic Solar Cells written by Zhenghao Mao and published by . This book was released on 2014 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic solar cells (OSCs), consisted of carbon-based organic semiconductors, either polymers or small molecules, have recently attracted the attention of both academic and industry due to their unique properties such as easy processing, flexibility and scalability. One major limitation toward commercialization is the low power conversion efficiency (PCE) compared to inorganic solar cells. Thus, much research in this field is focused on improving the efficiency. A better understanding to the relationship between the properties of organic semiconductors and the solar device performance is required. In this thesis, perfluorinated-end modified poly(3-hexylthiophene), core-substituted naphthalene diimide, and Zn (II) complexes with azadipyrromethene were investigated. Their properties and applications in organic photovolatic (OPV) are discussed.Previous studies suggested that end-group modification of P3HT affects device efficiency, and that some fluorine in the end group slightly improve the efficiency. In order to further understand how perfluorinated end-groups affect device performance of blends of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl) propyl-1-phenyl [6, 6] C61 (PCBM), we synthesized a series of well-defined P3HT with differing perfluoroalkyl length by Stille coupling of the bromine end of P3HT and stannylated 2-perfluoroalkylthiophene. The reactions occurred quantitatively, confirmed by 1H and 19F NMR spectroscopy, and by MALDI-ToF mass spectroscopy. Electron filtering transmission electron microscopy (EF-TEM) revealed that the polymer/PCBM phase separate on the nanoscale. However, solar cells of the modified P3HTs with PCBM had a lower power conversion efficiency than that of un-modified P3HT:PCBM, suggesting that perfluoroalkyl end-groups are detrimental to solar cell performance.The performance of solution-processed organic photovoltaic is seriously limited by the absorption and energy tuning potential of fullerene-based electron acceptors. Overcoming these limitations requires the development of non-fullerene acceptors. Core-substituted naphthalene diimides (cNDI) are good candidates as non-fullerene acceptors for organic photovoltaic, because they have high electron affinity, excellent electron transport properties, and tunable energy levels. We synthesized several cNDIs with different imide core substituents and different alkylamino substituents (RF1-6). Their optical and electrochemical properties and OPV device properties as electron acceptors were studied. Particularly, RF1 was investigated as electron accepting material for optimization of solar cells. The LUMO energy level of RF1 is -3.7 eV, higher than PCBM (-4.0 eV); correspondingly, a high Voc (~1 V) can be reached from blends of P3HT and RF1. The power conversion efficiency improves from 0.31% (as-casted) or 0.48% (pre-annealed) to 0.96% with a processing 1,8-diiodooctane(DIO) additive at an optimum concentration of 0.2 vol%. The results are explained by changes in morphology observed by atomic force microscopy (AFM) and transmitting electron microscopy (TEM) images. Charge transport properties were estimated by space-charge limited current (SCLC) model, indicating that the electron mobility determines the OSC performance.One reason why efficiency of non-fullerene based solar cell have been relatively low is partly because non-fullerene acceptors are often planar and tend to form unfavorable phase-separated domains when blended with typical donors. We synthesized and characterized a series of new solution-processable azadipyromethene-based complexes, Zn(WS1-5)2. These new complexes have high electron affinity and strong accepting properties, and behave as good electron acceptors in organic solar cells. The best device performance was obtained from Zn(WS3)2 acceptor. The 3D nature of this acceptor prevents crystallization and promotes a favorable nanoscale morphology to give a high PCE of 4.10%. The acceptor also significantly contributed to photocurrent generation by harvesting light between 600 nm and 800 nm. These results demonstrate a new paradigm to designing acceptors with tunable properties that can overcome the limitations of fullerenes.

Download or read book Organic Solar Cells Towards High Efficiency written by Chuandao Charlie Wang and published by Open Dissertation Press. This book was released on 2017-01-26 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Organic Solar Cells Towards High Efficiency: Plasmonic Effects and Interface Engineering" by Chuandao, Charlie, Wang, 王传道, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Organic solar cells (OSCs) are promising candidates for solar light harvesting due to their standout advantages both in material properties and manufacturing process. During past decades, remarkable progress has been achieved. Efficiency for single-junction cells over 9% and tandem cells over 10% has been reported. For high performance OSCs towards commercialization, sufficient light absorption and high quality buffer layers are still two challenges, which are addressed in this thesis by investigating the plasmonic effects on OSCs and interface engineering. Here, the mechanisms of plasmonic effects on OSC are explored by incorporating metallic Au nanoparticles (NPs) in individual anode buffer layer and active layer, respectively, and finally in both layers simultaneously. When Au NPs are incorporated into the buffer layer, surface plasmonic resonance (SPR) induced absorption enhancement due to incorporation of Au NPs is evidenced theoretically and experimentally to be only minor contributor to the performance improvement. The increased interfacial contact area between the buffer layer and active layer, together with the reduced resistance of the buffer layer due to the embedded Au NPs, are revealed to benefit hole collection and thus are main contributors to the performance improvement. When Au NPs are embedded in the active layer, Au NPs induced SPR indeed contributes to enhanced light absorption. However, when large amount of Au NPs are incorporated, the negative effects of NPs on the electrical properties of OSCs can counter-diminish the optical enhancement from SPR, which limits the overall performance improvement. When Au NPs are embedded into both layers, both advantages of incorporating NPs in individual layers can be utilized together to achieve more pronounced improvement in photovoltaic performance; as a result, accumulated enhancements in device performance can be achieved. The results herein are applicable to other metallic NPs such as Ag NPs, Pt NPs, etc. The study herein has clarified the degree of contribution of SPR effects on OSCs and revealed the mechanisms behind. It has also highlighted the importance of considering both optical and electrical effects when employing metallic NPs as strategies to enhance the photovoltaic performance of OSCs. Consequently, the study contributes both physical understanding and technological development of applying metallic NPs on OSCs. Regarding interface engineering, we first propose a simple method to modify the substrate work function for efficient hole collection by using an ultra-thin ultraviolet-ozone treated Au. The method can be used in other situations such as modifying the work function of multilayer graphene as transparent electrode. Then we propose a general method to synthesize solution-processed transition metal oxides (TMOs). Besides high material quality, desirable electrical properties, and good stability, our method stands out particular in that the synthesized TMOs can be dispersed in water-free solvents and the TMO films require only low temperature treatment, which is very compatible with the organic electronics. Our method can also be used to synthesize other TMOs other than the demonstrated molybdenum oxide and vanadium oxide. The proposed method herein is applicable in semiconductor industry. DOI: 10.5353/th_b4832965 Subjects: Solar cells

Download or read book Investigation of Device Performance and Interfacial Electronic Structures of Inverted Organic Solar Cells written by 羅鴻 and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Plasmonic Organic Solar Cells written by Bo Wu and published by Springer. This book was released on 2016-10-04 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book explores the incorporation of plasmonic nanostructures into organic solar cells, which offers an attractive light trapping and absorption approach to enhance power conversion efficiencies. The authors review the latest advances in the field and discuss the characterization of these hybrid devices using a combination of optical and electrical probes. Transient optical spectroscopies such as transient absorption and transient photoluminescence spectroscopy offer powerful tools for observing charge carrier dynamics in plasmonic organic solar cells. In conjunction with device electrical characterizations, they provide unambiguous proof of the effect of the plasmonic nanostructures on the solar cells’ performance. However, there have been a number of controversies over the effects of such integration – where both enhanced and decreased performance have been reported. Importantly, the new insights into the photophysics and charge dynamics of plasmonic organic solar cells that these spectroscopy methods yield could be used to resolve these controversies and provide clear guidelines for device design and fabrication.