Hole-conducting Polymer Research Articles

Highly Rectifying Water-Mediated Hydrogen Bond-Coupled Organic-Inorganic Interfaces.

Asymmetrically conducting interfaces are the building blocks of electronic devices. While p-n junction diodes made of seminal inorganic semiconductors with rectification ratios close to the theoretical limits are routinely fabricated, the analogous organic-inorganic and organic-organic interfaces are still too leaky to afford functional use. We report fabricating highly rectifying organic-inorganic interfaces by forming water-mediated hydrogen bonds between the hydrophilic surfaces of a hole-conducting polymer anode and a polycrystalline n-type metal oxide cathode. These hydrogen bonds simultaneously strengthen the anode-cathode electronic coupling, facilitate the matching between their incompatible surface structures, and passivate the detrimental surface imperfections. Compared to an analogous directly joined interface, our hydrogen-bonded Au-PEDOT:PSS-H2O-TiO2-Ti diodes demonstrate 105 times higher rectification ratios. These results illustrate the strong electronic coupling power of the hydrogen bonds on a macroscopic scale and underscore the hydrogen-bonded interfaces as the building blocks of fabricating organic electronic and optoelectronic devices. The presented interface model is anticipated to advance designing electronic devices based on the organic-organic and organic-inorganic hetero-interfaces. Described electronic implications of hydrogen bonding on the conductive polymer interfaces are anticipated to be impactful in the organic electronics and neuromorphic engineering.

Electrochemically Synthesized Poly(3-hexylthiophene) Nanowires as Photosensitive Neuronal Interfaces.

Poly(3-hexylthiophene) (P3HT) is a hole-conducting polymer that has been intensively used to develop organic optoelectronic devices (e.g., organic solar cells). Recently, P3HT films and nanoparticles have also been used to restore the photosensitivity of retinal neurons. The template-assisted electrochemical synthesis of polymer nanowires advantageously combines polymerization and polymer nanostructuring into one, relatively simple, procedure. However, obtaining P3HT nanowires through this procedure was rarely investigated. Therefore, this study aimed to investigate the template-assisted electrochemical synthesis of P3HT nanowires doped with tetrabutylammonium hexafluorophosphate (TBAHFP) and their biocompatibility with primary neurons. We show that template-assisted electrochemical synthesis can relatively easily turn 3-hexylthiophene (3HT) into longer (e.g., 17 ± 3 µm) or shorter (e.g., 1.5 ± 0.4 µm) P3HT nanowires with an average diameter of 196 ± 55 nm (determined by the used template). The nanowires produce measurable photocurrents following illumination. Finally, we show that primary cortical neurons can be grown onto P3HT nanowires drop-casted on a glass substrate without relevant changes in their viability and electrophysiological properties, indicating that P3HT nanowires obtained by template-assisted electrochemical synthesis represent a promising neuronal interface for photostimulation.

Red-light sensitized hole-conducting polymer for energy conversion.

We report a novel hole conductive polymer with photoactive Os(ii) complexes in the side chains. This PPV derivative can be activated upon absorption of red visible light and delivers notable photocurrents when used as photocathode material. Thus, the polymer presents as a stepping stone towards developing soft matter alternatives to NiO photocathodes, which function under visible light irradiation. To show the concept we combine electrical impedance spectroscopy with steady state spectroscopy. As light-driven hole injection from Os complex to the PPV polymer is thermodynamically feasible both based on reductive quenching of photoexcited PPV and based on oxidative quenching of the photoexcited Os chromophores we investigate the impact of illumination wavelengths on the photocathode behavior and photochemical stability of the material. While both blue and red light excitation, i.e., excitation of the chromophoric units PPV and excitation of the metal-to-ligand charge transfer transitions in the side-chain pendant Os chromophores yield cathodic photocurrents, the photochemical stability is drastically enhanced upon red-light excitation. Hence, the results of the investigations discussed show the validity of the concept developing red-light sensitized hole-conducting polymers for energy conversion.

The Effect of Dopant-Free Hole-Transport Polymers on Charge Generation and Recombination in Cesium-Bismuth-Iodide Solar Cells.

The photovoltaic characteristics of CsBi3 I10 -based solar cells with three dopant-free hole-conducting polymers are investigated. The effect on charge generation and charge recombination in the solar cells using the different polymers is studied and the results indicate that the choice of polymer strongly affects the device properties. Interestingly, for the solar cell with poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1), the photon-to-current conversion spectrum is highly improved in the red wavelength region, suggesting that the polymer also contributes to the photocurrent generation in this case. This report provides a new direction for further optimization of Bi-halide solar cells by using dopant-free hole-transporting polymers and shows that the energy levels and the interaction between the Bi-halide and the conducting polymers are very important for solar cell performance.

Stable and durable CH3NH3PbI3 perovskite solar cells at ambient conditions

Degradation of metal−organic halide perovskites when exposed to ambient conditions is a crucial issue that needs to be addressed for commercial viability of perovskite solar cells (PSCs). Here, a concept of encapsulating CH3NH3PbI3 perovskite crystals with a multi-functional graphene–polyaniline (PANI) composite coating to protect the perovskite against degradation from moisture, oxygen and UV light is presented. Hole-conducting polymers containing 2D layered sheet materials are presented here as multi-functional materials with oxygen and moisture impermeability. Specific studies involving PANI and graphene composites as coatings for perovskite crystals exhibited resistance to moisture and oxygen under continued exposure to UV and visible light. Most importantly, no perovskite degradation was observed even after 96 h of exposure of the PSCs to extremely high humidity (99% relative humidity). Our observations and results on perovskite protection with graphene/conducting polymer composites open up opportunities for glove-box-free and atmospheric processing of PSCs.

New insights into morphology of high performance BHJ photovoltaics revealed by high resolution AFM.

Direct imaging of the bulk heterojunction (BHJ) thin film morphology in polymer-based solar cells is essential to understand device function and optimize efficiency. The morphology of the BHJ active layer consists of bicontinuous domains of the donor and acceptor materials, having characteristic length scales of several tens of nanometers, that reduces charge recombination, enhances charge separation, and enables electron and hole transport to their respective electrodes. Direct imaging of the morphology from the molecular to macroscopic level, though, is lacking. Though transmission electron tomography provides a 3D, real-space image of the morphology, quantifying the structure is not possible. Here we used high-resolution atomic force microscopy (AFM) in the tapping and nanomechanical modes to investigate the BHJ active layer morphology that, when combined with Ar(+) etching, provided unique insights with unparalleled spatial resolution. PCBM was seen to form a network that interpenetrated into the fibrillar network of the hole-conducting polymer, both being imbedded in a mixture of the two components. The free surface was found to be enriched with polymer crystals having a "face-on" orientation and the morphology at the anode interface was markedly different.

Carrier transport mechanisms of hybrid ZnO nanorod-polymer LEDs

A hybrid polymer-nanorod (NR) light-emitting diode (LED), consisting of a hole-conducting polymer poly (9-vinyl carbazole) (PVK) and ZnO nanorod (NR) composite, with the device structure of glass/indium-tin-oxide (ITO)/PEDOT:PSS/(PVK + ZnO nanorods)/Al is fabricated through a simple spin coating technique. TEM images shows inhomogeneous deposition and the agglomeration of ZnO NRs, which is explained through their low probability of adsorption on PVK due to two-dimensional structural property. In the current-voltage characteristics, negative differential resistance (NDR) phenomenon is observed corresponding to device structure without ZnO NRs. The carrier transport behavior in the LED device is well described by both ohmic and space-chargelimited-current (SCLC) mechanisms. Broad blue electroluminescence (EL) consisting of two sub peaks, are centered at 441 nm and the other at 495 nm, is observed, which indicates that the ZnO nanorod play a role as a recombination center for excitons. The red shift in the position of the EL compared to that photoluminescence is well explained through band offsets at the heterojunction between the PVK and ZnO NRs.

Synthesis and Characterization of the Hole-Conducting Silica/Polymer Nanocomposites and Application in Solid-State Dye-Sensitized Solar Cell

Hole-conducting silica/polymer nanocomposites exhibit interesting physical and chemical properties with important applications in the field of energy storage and hybrid solar cells. Although the conventional strategy of grafting hole-conducting polymer onto the surface of silica nanoparticles is to use in situ oxidative polymerization, a promising alternative of using surface-initiated controlled living radical polymerization has arisen to anchor the polymer on the silica. The resulting silica/polymer nanocomposites from the latter method are more chemically and thermally stable because of the strong covalent bonding compared to the electrostatic interaction from in situ polymerization. The use of these nanocomposites mixed with spiro-MeOTAD (2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene) as a new hole conductor in the application of solid-state dye-sensitized solar cell (ss-DSSC) is reported here. The power conversion efficiency of this ss-DSSC is higher than the full spiro-MeOTAD ss-DSSC. Notably, the short circuit current improves by 26%. It is explained by large size silica/polymer nanocomposites forming an additional light scattering layer on the top of photoanode. This is the first time a conductive light scattering layer is introduced into ss-DSSC to enhance cell performance.

Infiltration of Polymer Hole-Conductor into Mesoporous Titania Structures for Solid-State Dye-Sensitized Solar Cells

The degree of filling of titania nanostructures with a solid hole-conducting material is important for the performance of solid-state dye-sensitized solar cells (ssDSSCs). Different ways to infiltrate the hole-conducting polymer poly(3-hexylthiophene) (P3HT) into titania structures, both granular structures as they are already applied commercially and tailored sponge nanostructures, are investigated. The solar cell performance is compared to the morphology determined with scanning electron microscopy (SEM) and time-of-flight grazing incidence small-angle neutron scattering (TOF-GISANS). The granular titania structure, commonly used for ssDSSCs, shows a large distribution of particle and pore sizes, with porosities in the range from 41 to 67%, including even dense parts without pores. In contrast, the tailored sponge nanostructure has well-defined pore sizes of 25 nm with an all-over porosity of 54%. Filling of the titania structures with P3HT by solution casting results in a mesoscopic P3HT overlayer and consequently a bad solar cell performance, even though a filling ratio of 67% is observed. For the infiltration by repeated spin coating, only 57% pore filling is achieved, whereas filling by soaking in the solvent with subsequent spin coating yields filling as high as 84% in the case of the tailored titania sponge structures. The granular titania structure is filled less completely than the well-defined porous structures. The solar cell performance is increased with an increasing filling ratio for these two ways of infiltration. Therefore, filling by soaking in the solvent with subsequent spin coating is proposed.

Information media based on electron-donor oligomers

Routes for designing hole-conducting organic polymers for use in photoelectric solar-energy converters and light emitters and primarily for recording, storage, and processing of optical information are considered. New carbazole-containing radially tetrasubstituted silanes and germanes are described. It is shown that the information characteristics of holographic recording media based on oligomer compositions substantially depend on the shapes of the oligomer macromolecules.

A GaN nanoneedle inorganic/organic heterojunction structure for optoelectronic devices

We studied an inorganic/organic hybrid heterostructure for optoelectronic device and applications. The structure was fabricated using inorganic material consisting of GaN nanoneedles and the hole-conducting polymer PEDOT:PSS. A PEDOT:PSS layer with a thickness of ∼50nm was deposited using spin coating on GaN nanoneedles grown using an HVPE system. To elucidate the effects of the nanostructure, we compared the properties of the GaN nanoneedle/PEDOT:PSS structure with those of a GaN epilayer/PEDOT:PSS structure. The GaN nanoneedle/PEDOT:PSS structure showed a broader, shifted emission peak in the PL measurements compared with the GaN epilayer/PEDOT:PSS structure, as well as a lower turn-on voltage when the I–V characteristics were measured.

Combining a Small Hole-Conductor Molecule for Efficient Dye Regeneration and a Hole-Conducting Polymer in a Solid-State Dye-Sensitized Solar Cell

In dye-sensitized solar cells (DSC) an efficient transfer of holes from the oxidized dye to the contact is necessary, which in solid-state DSC is performed by hole-conductor molecules. In this report we use photoinduced absorption and transient absorption spectroscopy to show that a small hole-conducting molecule, tris(p-anisyl)amine, regenerates dye molecules in the pores of the dye-sensitized TiO2 nanoparticle electrode efficiently even for thick (>5 μm) electrodes. For similar thicknesses we observe incomplete regeneration using a larger polymer hole-conductor. However, the performance of the solar cells with the small hole-conductor molecules is poor due to that inefficient hole conduction in these small molecules may limit the collection of the charges at the contacts. Polymer hole-conductors, which may have a good hole conductivity, also have a high molecular weight, which makes these polymers difficult to infiltrate into the smallest pores in the electrode. We show that a conducting polymer, P3HT, may be added to the small molecule hole-conductor, to enable better transport of the charges to the contact and to reduce recombination and therefore increase the photocurrent. This new device construction with a small molecule efficiently regenerating the dye molecules, and a polymer conducting the holes to the contact is therefore a promising pathway for solid-state dye-sensitized solar cells.

Efficient HgTe colloidal quantum dot-sensitized near-infrared photovoltaic cells

We have demonstrated the successful fabrication of multiple-layer colloidal quantum dot (CQD)-sensitized near-infrared (NIR) photovoltaic (PV) cells using the solution processable HgTe CQDs and poly-3-(hexylthiophene) (P3HT) as hole-conducting polymer. The cells showed a 3.6 fold enhancement in power conversion efficiency under NIR light illumination by the post-ethanedithiol chemical treatment. The performance enhancement was mainly ascribed to the improved interfacial contact between HgTe CQDs by elimination of oleic acid as capping ligand on the surface of HgTe CQDs. In addition, the HgTe CQD-sensitized PV cells could effectively detect weak NIR light and process over 1 kHz level signals.

Bioinspired hole-conducting polymers for application in organic light-emitting diodes

Download options Please wait... Supplementary files Supplementary information PDF (600K) Article information DOI https://doi.org/10.1039/C2JM32665E Article type Communication Submitted 27 Apr 2012 Accepted 19 Jul 2012 First published 20 Jul 2012 Download Citation J. Mater. Chem., 2012,22, 18127-18131 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Bioinspired hole-conducting polymers for application in organic light-emitting diodes C. Cheng, Y. Chu, P. Huang, Y. Yen, C. Chu, A. C.-M. Yang, F. Ko, J. Chen and F. Chang, J. Mater. Chem., 2012, 22, 18127 DOI: 10.1039/C2JM32665E To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Chih-Chia Cheng Yu-Lin Chu Pei-Hsiu Huang Ying-Chieh Yen Chih-Wei Chu Arnold C.-M. Yang Fu-Hsiang Ko Jem-Kun Chen Feng-Chih Chang

Enhancing the device performance of Sb2S3-sensitized heterojunction solar cells by embedding Au nanoparticles in the hole-conducting polymer layer

Performance of Sb(2)S(3)-sensitized heterojunction solar cells is enhanced by embedding Au nanoparticles in the poly-3-hexylthiophene (P3HT) hole-conducting polymer layer. The improved charge transfer/transport at the Sb(2)S(3)/P3HT/Au interface by extended interface area of the P3HT/Au counter electrode and the re-absorption of the backscattering light from the embedded Au nanoparticles enhanced the device performance: J(sc) 11.0 to 12.8 mA cm(-2), V(oc) 606 to 626 mV, fill factor (FF) 60.5 to 61.2%, and power conversion efficiency (η) 4.0 to 4.9%. Simultaneous enhancement of V(oc), J(sc), and FF in Au nanoparticle-embedded systems is mainly attributed to the improved charge collection efficiency and light harvesting efficiency of Sb(2)S(3) due to the improved charge transfer/transport in the Sb(2)S(3)/P3HT/Au interface.

Effects of Intercalation on the Hole Mobility of Amorphous Semiconducting Polymer Blends

Fullerenes have been shown to intercalate between the side chains of many crystalline and semicrystalline polymers and to affect the properties of polymer:fullerene bulk heterojunction solar cells. Here we present the first in-depth study of intercalation in an amorphous polymer. We study blends of the widely studied amorphous polymer poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) with a variety of molecules using photoluminescence measurements, scanning electron microscopy, and space-charge limited current mobility measurements. The blends with elevated hole mobilities exhibit complete photoluminescence quenching and show no phase separation in a scanning electron microscope. We conclude that intercalation occurs in MDMO-PPV:fullerene blends and is responsible for the increase in the MDMO-PPV hole mobility by several orders of magnitude when it is blended with fullerenes, despite the dilution of the hole-conducting polymer with an electron acceptor.

Soft-Etch Mesoporous Hole-Conducting Block Copolymer Templates

We present a mesoporous hole-conducting polymer film resulting from spontaneous block copolymer self-assembly based on a simple spin-coating protocol. A diblock copolymer consisting of a triphenylamine side group polymer and a poly(d,l-lactide) block (PSTPA-b-PLA) is shown to microphase separate to form ordered 13 nm cylindrical PLA microdomains embedded in the semiconducting PSTPA matrix. Partially ordered and film-spanning PLA domains could be identified in films immediately after spin coating from toluene solutions on conducting substrates. Selective mild etching of the minority PLA domains (in weak aqueous base) leads to a mesoporous hole-conducting polymer matrix. The pore structure is replicated electrochemically in platinum, demonstrating the viability of this approach to producing nano-organized heterojunction structures in thin films.

Influence of the sensitizer reduction potential on the sensitivity of photorefractive polymer composites

We report on a series of near infrared (NIR)-sensitive photorefractive polymer composites (PPCs) based on the hole-conducting polymer PF6-TPD, which are sensitized by soluble fullerene-derivatives as electron-accepting agents. We demonstrate a direct correlation between the electron accepting capability of the sensitizer and the holographic response time. The holographic recording speed is found to improve by one order of magnitude when lowering the reduction potential of the sensitizer by approx. 400 mV, while all other physical parameters of the materials remain essentially identical. Furthermore, the lifetime of the mobile charge carriers is found to correlate linearly with the reduction potential, thus indicating a decrease in recombination rates for stronger accepting capability of the sensitizer. Finally, we found that pre-illumination enhanced the holographic sensitivity. The effect is found to be most pronounced for the strongest acceptor due to reduced recombination of the preformed carriers. Overall, the PPCs reported here feature the currently highest sensitivity in the NIR spectral region.

Transient reverse current phenomenon in a p-n heterojunction comprised of poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) and ZnO nanowall

We report the characteristics of a p-n heterojunction diode comprised of a poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) as the hole-conducting p-type polymer and n-type ZnO nanowall networks. ZnO nanowall networks were synthesized on a GaN/sapphire substrate without metal catalyst using hot-wall type metal organic chemical vapor deposition. The p-n heterojunction diodes of PEDOT:PSS/ZnO nanowall exhibited a space charge limited current phenomena at forward bias and a transient reverse current recovery when a sudden reverse bias was applied from the forward bias condition. The minority carrier lifetime was estimated to be ∼2.5 μs.

Influence of Doped Anions on Poly(3,4-ethylenedioxythiophene) as Hole Conductors for Iodine-Free Solid-State Dye-Sensitized Solar Cells

Poly(3,4-ethylenedioxythiophene) (PEDOT) is an excellent hole-conducting polymer able to replace the liquid I(-)/I3(-) redox electrolyte in dye-sensitized solar cells (DSCs). In this work we applied the in situ photoelectropolymerization technique to synthesize PEDOT and carried out a careful analysis of the effect of different doping anions on overall solar cell performance. The anions analyzed in this work are ClO4(-), CF3SO3(-), BF4(-), and TFSI(-). The best solar cell performance was observed when the TFSI(-) anion was used. Photoelectrochemical and impedance studies reveal that the doped anions in the PEDOT hole conductor system have great influences on I-V curves, conductivity, and impedance. The optimization of these parameters allowed us to obtain an iodine-free solid-state DSC with a maximum J(sc) of 5.3 mA/cm2, V(oc) of 750 mV, and a conversion efficiency of 2.85% which is the highest efficiency obtained so far for an iodine-free solid-state DSC using PEDOT as hole-transport material.