Bacteriorhodopsin-based Langmuir-Schaefer films for solar energy capture

The photovoltaic (PV) solar cell, converting incident solar radiation directly into electrical energy, today represents the most common power source for the Earth-orbiting spacecraft, and the utilization of organic materials in this context is here explored in comparison with the present state of the art placing emphasis in organic nanotechnology. Poly[3-3'(vinylcarbazole)] (PVK) was synthesized by oxidative polymerization with ferric chloride of N-vinylcarbazole. The resulting polymer was then deposited on solid support by using the Langmuir-Schaefer (LS) technique. The pressure-area isotherm of PVK revealed the possibility of compact monolayer formation at the air-water interface. Different layers of PVK were doped with iodine vapors. The cyclic voltammetry investigation of PVK-doped I/sub 2/ showed a distinctive electrochemical behavior. The photoinduced charge transfer across a donor/acceptor (D/A) hybrid interface provided an effective method to study the PV properties of the composite LS films. The results are compared with other approaches within the biological framework, such as bacteriorhodopsin (BR), and organic nanostructured materials.     

Investigation of exciton photodissociation, charge transport and photovoltaic response of poly(N-vinyl carbazole):TiO(2) nanocomposites for solar cell applications

The photogeneration of charge carriers in spin-coated thin films of nanocrystalline (nc-)TiO(2) particles dispersed in a semiconducting polymer, poly(N-vinylcarbazole) (PVK), has been studied by photoluminescence and charge transport measurements. The solvent and the TiO(2) particle concentration have been selected to optimize the composite morphology. A large number of small domains leading to a large interface and an improved exciton dissociation could be obtained with tetrahydrofuran (THF). The charge transport mechanism and trap distribution at low and high voltage in ITO/nc-TiO(2):PVK/Al diodes in the dark could be identified by current-voltage measurements and impedance spectroscopy. The transport mechanism is space charge limited with an exponential trap distribution in the high voltage regime (1-4?V), whereas a Schottky process with a barrier height of about 0.9?eV is observed at low bias voltages (<1?V). The current-voltage characteristics under white illumination have shown a dramatic increase of the short circuit current density J(sc) and open circuit voltage V(oc) for a 30% TiO(2) volume content corresponding to the morphology exhibiting the best dispersion of TiO(2) particles. A degradation of the photovoltaic properties is induced at higher compositions by the formation of larger TiO(2) aggregates. A procedure has been developed to extract the physical parameters from the J-V characteristics in the dark and under illumination on the basis of an equivalent circuit. The variation of the solar cell parameters with the TiO(2) composition confirms that the photovoltaic response is optimum for 30% TiO(2) volume content. It is concluded that the photovoltaic properties of nc-TiO(2):PVK nanocomposites are controlled by the interfacial area between the donor and the acceptor material and are limited by the dispersion of the TiO(2) nanoparticles in the polymer.     

Naphthalenediimide (NDI) polymers for all-polymer photovoltaics

Naphthalenediimide (NDI) polymers are an important class of electron-accepting (acceptor or n-type) semiconductors for organic photovoltaic (OPV) or organic solar cell (OSC) applications. Blending them with compatible electron-donating (donor or p-type) polymers yields an OPV device known as bulk-heterojunction (BHJ) all-polymer solar cells (all-PSCs). Compared to the more extensively studied OPVs using fullerene derivatives as the acceptor material, all-PSCs provide important benefits such as chemical tunability, mechanical flexibility and ambient/stress stability. Through an extensive research on materials design and device optimization in the last five years, all-PSCs employing NDI-based polymers have achieved remarkable improvement in device power conversion efficiency (PCE), now surpassing 10% – a number that approaches the state-of-the-art organic photovoltaic (OPV) cells using fullerenes. In this review, recent development of NDI-based conjugated polymers used in all-PSCs will be highlighted.     

Improving Cooperative Interactions Between Halogenated Aromatic Additives and Aromatic Side Chain Acceptors for Realizing 19.22% Efficiency Polymer Solar Cells

Processing additive plays an important role in the standard operation procedures for fabricating top performing polymer solar cells (PSCs) through efficient interactions with key photovoltaic materials. However, improving interaction study of acceptor materials to high performance halogenated aromatic additives such as diiodobenzene (DIB) is a widely neglected route for molecular engineering toward more efficient device performances. In this work, two novel Y-type acceptor molecules of BTP-TT and BTP-TTS with different aromatic side chains on the outer positions are designed and synthesized. The resulting aromatic side chains significantly enhanced the interactions between the acceptor molecules and DIB through an arene/halogenated arene interaction, which improved the crystallinity of the acceptor molecules and induced a polymorph with better photovoltaic performances. Thus, high power conversion efficiencies (PCEs) of 18.04% and 19.22% are achieved in binary and ternary blend devices using BTP-TTS as acceptor and DIB as additive. Aromatic side chain engineering for improving additive interactions is proved to be an effective strategy for achieving much higher performance photovoltaic materials and devices.     

以聚芴为主体的高效红光磷光聚合物发光二极管

以笼型多面体硅氧烷(poss)封端的聚烷基芴PFO-poss和PVK为主体,红光磷光络合物Ir(piq)为客体制作了不同结构的器件,最终在以PFO-poss为主体的双层结构器件当中获得了5.48cd/A的电致发光效率,超过了以PVK为主体的器件效率水平.研究了以PFO-poss为主体的器件中PVK的作用,发现作为空穴传...     

水溶胶CdSe纳米复合器件电致发光特性的研究

以巯基乙酸为稳定剂在水相中制备了水溶胶CdSe纳米晶,透射电子显微镜表明了纳米晶的形态和尺寸大小.用表面活性剂将CdSe纳米晶从水相中转移到有机相中,将其与具有空穴传输性能的聚合物PVK互溶在一起作为电致发光器件的发光层,以Alq3作为电子传输层,在发光层与Alq3之间加入了空穴阻挡层BCP制备了多层电致发光器件,研究了不同CdSe/PVK配比下水溶胶CdSe纳米复合器件的电致发光特性,结果发现随着水溶胶CdSe纳米晶在纳米复合物中所占比例的降低,电致发光器件的发光强度有所提高,起亮电压有所降低.     

Investigation of post-thermal annealing-induced enhancement in photovoltaic performance for squaraine-based organic solar cells

In this work, we have systematically investigated the post-thermal annealing-induced enhancement in photovoltaic performance of a 2,4-bis[4-(N, N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIBSQ)/C₆₀ planar heterojunction (PHJ) organic solar cells (OSCs). An increased power conversion efficiency (PCE) of 3.28% has been realized from a DIBSQ/C₆₀ device with thermal annealing at 100 °C for 4 min, which is about 33% enhancement compared with that of the as-cast device. The improvement of the device performance may be mainly ascribed to the crystallinity of the DIBSQ film with post-thermal annealing, which will change the DIBSQ donor and C₆₀ acceptor interface from PHJ to hybrid planar-mixed heterojunction. This new donor–acceptor heterojunction structure will significantly improve the charge separation and charge collection efficiency, as well as the open circuit voltage (V_oc) of the device, leading to an enhanced PCE. This work provides an effective strategy to improve the photovoltaic performance of SQ-based OSCs.     

Influence of the polymer matrix on the efficiency of hybrid solar cells based on silicon nanowires

Poly (N-vinylcarbazole) (PVK):SiNWs and poly (2-methoxy, 5-(2-ethyl-hexyloxy)-p-phenyl vinylene) (MEH-PPV):SiNWs bulk-heterojunctions (BHJ) have been elaborated from blends of SiNWs and the polymer in solution from a common solvent. Optical properties of these nanocomposites have been investigated by UV-vis absorption and photoluminescence (PL) spectral measurements. We have studied the charge transfer between SiNWs and the two polymers using the photoluminescence quenching of PVK and MEH-PPV which is a convenient signature of the reduced radiative recombination of the generated charge pairs upon exciton dissociation. We found that PVK and SiNWs constitutes the better donor-acceptor system. In order to understand the difference between PVK:SiNWs or MEH-PPV:SiNWs behaviours, photoluminescence responses were correlated with the topography (SEM) of the thin films. The photovoltaic effect of ITO/PEDOT:PSS/SiNWs:PVK/Al and ITO/PEDOT:PSS/SiNWs:MEH-PPV/Al structures was studied by current-voltage (I-V) measurements in dark and under illumination and interpreted on the basis of the charge transfer differences resulting from the morphologies.     

Nanomaterials for photovoltaic conversion

A promising route for photovoltaic conversion has emerged from the combination of electroactive nanomaterials and small bandgap polymers. The formation of bulk heterojunctions resulting from the extended interfaces leads to efficient dissociation of the charge pairs generated under sunlight shown by the rapid extinction of the polymer photoluminescence for increasing contents of fullerenes or TiO₂ nanoparticles in MEH-PPV or PVK. Unconventional elaboration routes of the blends have been developed to increase the nanofiller dispersion and inhibit phase separation at high concentration. The size reduction of the acceptor domains led to a complete quenching of the radiative recombinations, obtained by specific solvent processing of MEH-PPV / C₆₀ nanocomposites or sol gel elaboration of TiO₂ nanoparticles in a PVK film. A simultaneous increase of the photocurrents could be achieved by the dispersion and size optimisation of the nanofillers. In situ generation of silver particles in MEH-PPV provides an example of enhanced charge separation induced by the plasmon resonance at the metal/polymer interface. The strong influence of the molecular morphology on the nanocomposite properties emphasizes the large improvements which can still be gained on the performances of organic solar cells.     

体相异质结型有机太阳能电池的研究进展

基于电子给/受体共混体系制备的体相异质结型有机太阳能电池是一种低耗、高效的有机光伏器件.作为器件核心,光电转化共混活性层的质量优劣会直接影响器件的能量转换效率.研究发现,不同的给/受体材料组成、2种材料的共混比例、共溶剂的选择以及器件的热退火处理等因素都可影响到活性层质量.结合上述研究热点,综述了体相异质结型有机太阳能电池近年来的研究进展,阐述了该研究领域下一步发展的重点、趋势及前景.     

Conformation‐Tuning Effect of Asymmetric Small Molecule Acceptors on Molecular Packing,Interaction, and Photovoltaic Performance

Understanding the conformation effect on molecular packing, miscibility, and photovoltaic performance is important to open a new avenue for small‐molecule acceptor (SMA) design. Herein, two novel acceptor–(donor‐acceptor1‐donor)–acceptor (A‐DA1D‐A)‐type asymmetric SMAs are developed, namely C‐shaped BDTP‐4F and S‐shaped BTDTP‐4F . The BDTP‐4F ‐based polymer solar cells (PSCs) with PM6 as donor, yields a power conversion efficiency (PCE) of 15.24%, significantly higher than that of the BTDTP‐4F ‐based device (13.12%). The better PCE for BDTP‐4F ‐based device is mainly attributed to more balanced charge transport, weaker bimolecular recombination, and more favorable morphology. Additionally, two traditional A‐D‐A‐type SMAs ( IDTP‐4F and IDTTP‐4F ) are also synthesized to investigate the conformation effect on morphology and device performance. Different from the device result above, here, IDTP‐4F with S‐shape conformation outperforms than IDTTP‐4F with C‐shape conformation. Importantly, it is found that for these two different types of SMA, the better performing binary blend has similar morphological characteristics. Specifically, both PM6:BDTP‐4F and PM6:IDTP‐4F blend exhibit perfect nanofibril network structure with proper domain size, obvious face‐on orientation and enhance donor‐acceptor interactions, thereby better device performance. This work indicates tuning molecular conformation plays pivotal role in morphology and device effciciency, shining a light on the molecular design of the SMAs.     

Enhanced performance of P3HT/TiO2 bilayer heterojunction photovoltaic device having gold nanoparticles in the donor layer

The photovoltaic effects of blending gold nanoparticles (AuNPs) into the donor layer of a poly(3-hexylthiophene) (P3HT)/TiO2 bilayer heterojunction device have been studied. P3HT was synthesized via the modified Gragnard metathesis method and AuNPs with sizes ranging from 12 to 15 nm were formed via a reduction of HAuCl4. The blending of AuNPs into P3HT caused a lower photoluminescence (PL) intensities and a decreased energy level of the highest occupied molecular orbital (HOMO) than the pristine P3HT owing to the good electron-accepting nature of AuNPs. Upon the use of P3HT-AuNPs as the donor layer, the decreased HOMO(donor) resulted in an increased open circuit voltage (V(OC)) and thus enabled the fabricated (P3HT-AuNPs)/TiO2 bilayer heterojunction photovoltaic device to have an improved power conversion efficiency of solar energy. V(OC) as well as the overall power conversion efficiency increased with an increase in the AuNP content as a result of additional interfaces which facilitated the charge separation of excitons and percolation pathways which enhanced the electron transfer to the TiO2 acceptor. Furthermore, unannealed P3HT-AuNPs exhibited nanoholes and provided photovoltaic devices a power conversion efficiency nearly two time higher than annealed P3HT-AuNPs.     

Nonvolatile flexible organic bistable devices fabricated utilizing CdSe/ZnS nanoparticles embedded in a conducting poly N-vinylcarbazole polymer layer

The bistable effects of CdSe/ZnS nanoparticles embedded in a conducting poly N-vinylcarbazole (PVK) polymer layer by using flexible poly-vinylidene difluoride (PVDF) and polyethylene terephthalate (PET) substrates were investigated. Transmission electron microscopy (TEM) images revealed that CdSe/ZnS nanoparticles were formed inside the PVK polymer layer. Current-voltage (I-V) measurement on the Al/[CdSe/ZnS?nanoparticles+?PVK]/ITO/PVDF and Al/[CdSe/ZnS nanoparticles+?PVK ]/ITO/PET structures at 300?K showed a nonvolatile electrical bistability behavior with a flat-band voltage shift due to the existence of the CdSe/ZnS nanoparticles, indicative of trapping, storing and emission of charges in the electronic states of the CdSe nanoparticles. A bistable behavior for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results. These results indicate that OBDs fabricated by embedding inorganic CdSe/ZnS nanoparticles in a conducting polymer matrix on flexible substrates are prospects for potential applications in flexible nonvolatile flash memory devices.     

Unraveling the Role of Non-Fullerene Acceptor with High Dielectric Constant in Organic Solar Cells

Increasing the relative dielectric constant is a constant pursuit of organic semiconductors, but it often leads to multiple changes in device characteristics, hindering the establishment of a reliable relationship between dielectric constant and photovoltaic performance. Herein, a new non-fullerene acceptor named BTP-OE is reported by replacing the branched alkyl chains on Y6-BO with branched oligoethylene oxide chains. This replacement successfully increases the relative dielectric constant from 3.28 to 4.62. To surprise, BTP-OE offers consistently lower device performance relative to Y6-BO in organic solar cells (16.27% vs 17.44%) due to the losses in open-circuit voltage and fill factor. Further investigations unravel that BTP-OE has resulted in reduced electron mobility, increased trap density, enhanced first order recombination, and enlarged energetic disorder. These results demonstrate the complex relationship between dielectric constant and device performance, which provide valuable implications for the development of organic semiconductors with high dielectric constant for photovoltaic application.     

Counterion effects in cyanine heterojunction photovoltaic devices

We investigated cyanine heterojunction photovoltaic devices using carbocyanine dyes as donors and buckminsterfullerene (C60) as acceptor. In particular, we focused on the influence of cyanine counterions on the photovoltaic device characteristics. It was found that counterions can be displaced in the applied electric field and give rise to important hystereses in the current-voltage characteristics, which are related to charge injection processes at electrode and organic heterointerfaces. Mobile counterions have also a drastic effect on the photocurrent spectrum and are responsible for an important C60 contribution at the organic heterojunction between cyanine and C60. If the counterion is covalently linked to the cyanine dye, the C60 contribution in the blue spectral domain can not be observed.     

Polymer Light-Emitting Diode Using a New Electrophosphorescent Cyclometalated Iridium Complex

A new iridium-based cyclometalated complex, namely bis (2-phenylpyridine-C², N') iridium (III) picolinate [(ppy)₂Ir(pic)] is synthesized and investigated as electrophosphorescent dopant in polymer-based organic light-emitting diodes. The photoluminescence emission from this complex is observed at 501 nm, with a shoulder at 526 nm. Poly(N-vinylcarbazole) (PVK) is used as host polymer and single-layer devices of PVK doped with (ppy)₂Ir(pic) complex are fabricated. Photoluminescence (PL) spectra of PVK films doped with different concentration of iridium complex were measured to study the possible energy transfer occurring between PVK to iridium complex. A predominant blue to a completely green shifted emission is observed when the doping concentration was increased from 0% to 5 wt%. Optical and atomic force microscopic images of the doped films indicate a smooth film formation when spin coated with chlorobenzene as a solvent as compared to chloroform. Electroluminescence spectra of ITO/PEDOT:PSS/PVK:(ppy)₂Ir(pic)/Al device resembles that of the PL spectra with emission at 507 nm and Commission Internationale de l'Eclairage (CIE) coordinates (0.29, 0.57).     

Polymer Photovoltaics with Alternating Copolymer/Fullerene Blends and Novel Device Architectures

The synthesis of novel conjugated polymers, designed for the purpose of photovoltaic energy conversion, and their properties in polymer/fullerene materials and photovoltaic devices are reviewed. Two families of main‐chain polymer donors, based on fluorene or phenylene and donor–acceptor–donor comonomers in alternating copolymers, are used to absorb the high‐energy parts of the solar spectrum and to give high photovoltages in combinations with fullerene acceptors in devices. These materials are used in alternative photovoltaic device geometries with enhanced light incoupling to collect larger photocurrents or to enable tandem devices and enhance photovoltage.     

Flexible Quasi-2D Perovskite/IGZO Phototransistors for Ultrasensitive and Broadband Photodetection

Organic–inorganic hybrid perovskites (PVKs) have recently emerged as attractive materials for photodetectors. However, the poor stability and low electrical conductivity still restrict their practical utilization. Owing to the quantum-well feature of two-dimensional (2D) Ruddlesden–Popper PVKs (2D PVKs), a promising quasi-2D PVK/indium gallium zinc oxide (IGZO) heterostructure phototransistor can be designed. By using a simple ligand-exchange spin-coating method, quasi-2D PVK fabricated on flexible substrates exhibits a desirable type-II energy band alignment, which facilitates effective spatial separation of photoexcited carriers. The device exhibits excellent photoresponsivity values of >10⁵ A W⁻¹ at 457 nm, and broadband photoresponse (457–1064 nm). By operating the device in the depletion regime, the specific detectivity is found to be 5.1 × 10¹⁶ Jones, which is the record high value among all PVK-based photodetectors reported to date. Due to the resistive hopping barrier in the quasi-2D PVK, the device can also work as an optoelectronic memory for near-infrared information storage. More importantly, the easy manufacturing process is highly beneficial, enabling large-scale and uniform quasi-2D PVK/IGZO hybrid films for detector arrays with outstanding ambient and operation stabilities. All these findings demonstrate the device architecture here provides a rational avenue to the design of next-generation flexible photodetectors with unprecedented sensitivity.     

Fabrication and characteristics of fullerene-perylene dyad based organic photovoltaic cell

Fullerene is an acceptor material which is used most usually in organic photovoltaic cell. By the way, the reduction of electron mobility and the phase separation of conducting polymer and fullerene in the actual bulk heterojunction photovoltaic cell limit further improvement of device performance. In order to overcome the problems, fabrication of hybrid planar mixed heterojunction cells and synthesis of donor-acceptor dyad have been studied. In the present work, we have synthesized fullerene-perylene dyad to improve the fullerene based photovoltaic cell. In order to explore the properties of the synthesized material, the measurements of absorption spectrum and energy level were carried out. We have investigated the energy conversion efficiency of organic photovoltaic cell consisting of ITO/PEDOT-PSS/MEH-PPV:fullerene-perylene dyad/Al.     

The effect of crystallinity in donor groups on the performance of photovoltaic devices based on an oligothiophene-fullerene dyad

Organic photovoltaic devices based on an oligothiophene-fullerene dyad mixed with either an oligothiophene as donor or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as acceptor were fabricated to improve charge carrier transport in the films. The origin of the device performance dependence on the mixing ratios was studied by atomic force microscopy and UV-vis absorption spectra and differential scanning calorimetry measurements. We found that the addition of the oligothiophene molecules improved the crystallinity of the donor groups in the film, resulting in a 20% increase in fill factor, while the addition of PCBM slightly lowered the crystallinity, thereby reducing the fill factor.