Hole-transporting Polymers Research Articles

Learning from hole-transporting polymers in regular perovskite solar cells to construct efficient conjugated polyelectrolytes for inverted devices

• A polyelectrolyte was designed with the same main-chain of a reported polymer HTM. • HTM based on it showed an efficiency of 19.92% in an inverted solar cell. • More thiophene unit gave a superior hole-extraction and defect-passivation ability. Owing to its high wettability and the resulting compatibility with the future industrial device fabrication process, the conjugated polyelectrolyte (CPE) has becoming a promising hole-transporting material (HTM) in the inverted perovskite solar cell (iPSC); however, only a few highly efficient CPEs have been reported probably due to the limited pool of molecular designing strategies. Here we construct a CPE named DTB(Na) with the same main-chain of a polymer DTB(EH) that was previously employed as a dopant-free HTM in a highly efficient regular type PSC (rPSC) and with simple water/alcohol soluble side-chains. Compared with its analog bearing the only variation of less thiophene units in the main-chain, DTB(Na) shows stronger capacities of hole-extraction and defect-passivation, which should be ascribed to the more intensive exposure of thiophene functional unit to the perovskite layer. As a result, the DTB(Na) iPSC device presents enhanced values on all the photovoltaic parameters and long-term stability, and a power conversion efficiency of 19.92% is realized. Our results demonstrate the feasibility for efficient polymeric HTMs in rPSCs and iPSCs to share the same main-chains, thus enriching the molecular designing strategies and probably expanding the library of efficient HTMs for iPSCs.

Methoxy-Functionalized Triarylamine-Based Hole-Transporting Polymers for Highly Efficient and Stable Perovskite Solar Cells

The hole-transporting layer is an essential component in a perovskite solar cell (PSC) and plays a key role in controlling both power conversion efficiency (PCE) and stability. Here, we report a ne...

Hole-Transporting Polymers Containing Partially Oxygen-Bridged Triphenylamine Units and Their Application for Perovskite Solar Cells

Hole-Transporting Polymers Containing Partially Oxygen-Bridged Triphenylamine Units and Their Application for Perovskite Solar Cells

Vapor-Phase Formation of a Hole-Transporting Thiophene Polymer Layer for Evaporated Perovskite Solar Cells.

Homogeneous layer formation on textured silicon substrates is essential for the fabrication of highly efficient monolithic perovskite silicon tandem solar cells. From all well-known techniques for the fabrication of perovskite solar cells (PSCs), the evaporation method offers the highest degree of freedom for layer-by-layer deposition independent of the substrate's roughness or texturing. Hole-transporting polymers with high hole mobility and structural stability have been used as effective hole-transporting materials (HTMs) of PSCs. However, the strong intermolecular interactions of the polymers do not allow for a layer formation via the evaporation method, which is a big challenge for the perovskite community. Herein, we first applied a hole-transporting terthiophene polymer (PTTh) as an HTM for evaporated PSCs via an in situ vapor-phase polymerization using iodine (I2) as a sublimable oxidative agent. PTTh showed high hole mobility of 1.2 × 10-3 cm2/(V s) and appropriate energy levels as HTM in PSCs (EHOMO = -5.3 eV and ELUMO = -3.3 eV). The PSCs with the in situ vapor-phase polymerized PTTh hole-transporting layer and a co-evaporated perovskite layer exhibited a photovoltaic conversion efficiency of 5.9%, as a proof of concept, and high cell stability over time. Additionally, the polymer layer could fully cover the pyramidal structure of textured silicon substrates and was identified as an effective hole-transporting material for perovskite silicon tandem solar cells by optical simulation.

Simultaneous hole transport and defect passivation enabled by a dopant-free single polymer for efficient and stable perovskite solar cells

Dopant-free hole-transporting polymers with simultaneous main-chain hole extraction/transport and side-chain defect passivation are developed for efficient and stable perovskite solar cells.

Ether-soluble hole-transporting polymers based on triphenylamine/phenothiazine moieties with shallow HOMO levels

Novel ether-soluble hole-transporting polymers with shallow HOMO levels were used as efficient electron donors of charge carrier generation layers for tandem OLEDs.

Hole-transporting diketopyrrolopyrrole-thiophene polymers and their additive-free application for a perovskite-type solar cell with an efficiency of 16.3%

Conjugated polymers of diketopyrrolopyrrole (DPP) and thiophene, especially 2,5-di-2-thienyl-thieno[3,2-b]thiophene, were characterized based on their molecular packing orientation, and they showed a π–π stacking distance of 3.6 A and a high field-effect hole mobility on the order of 10−2 cm2/Vs. Perovskite solar cells fabricated with the genuine or both oxidant- and salt dopant-free polymer as the hole-transporting layer displayed high photoconversion efficiencies of 16.3% as well as high durability. Conjugated polymers of diketopyrrolopyrrole (DPP) and thiophene, especially 2,5-di-2-thienyl-thieno[3,2-b]thiophene, were characterized by their molecular packing orientation with a π-π stacking distance of 3.6 A and a high field-effect hole mobility on the order of 10−2 cm2/Vs. A perovskite solar cell, fabricated with the genuine or both oxidizing and salt dopant-free polymer as a hole-transporting layer, displayed a high photo-conversion efficiency of 16.3% with high durability.

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.

Crosslinkable triphenylamine-based hole-transporting polymers for solution-processed polymer light-emitting diodes

Abstract We report the synthesis and characterization of a thermally crosslinkable hole-transporting poly(indenofluorene-co-triphenylamine) copolymer (X-IFTPA) containing a vinyl-functionalized triphenylamine moiety. This copolymer exhibited an exothermal peak at 125 °C in the first heating/cooling cycle of a differential scanning calorimetry study, indicating that crosslinking occurred. The highest occupied molecular orbital energy level of this copolymer was estimated to be −5.30 eV, as determined by cyclic voltammetry measurement. Flat and uniform films were formed by spin casting X-IFTPA from chlorobenzene solution. Crosslinking can be finished by thermally annealing the film at 150 °C for 24 min, which can be confirmed by reflectance Fourier transform infrared spectroscopy and UV–Vis absorption spectra. Multi-layer polymer light-emitting diodes (PLEDs) incorporating X-IFTPA as the hole transport layer and a green-light-emitting copolymer as the emissive layer exhibited enhanced luminous efficiency relative to that of a control device without a hole transport layer. Thus, the developed cross-linkable copolymer X-IFTPA is a promising material for the construction of efficient PLEDs.

Induced Infiltration of Hole-Transporting Polymer into Photocatalyst for Staunch Polymer-Metal Oxide Hybrid Solar Cells.

For efficient solar cells based on organic semiconductors, a good mixture of photoactive materials in the bulk heterojunction on the length scale of several tens of nanometers is an important requirement to prevent exciton recombination. Herein, we demonstrate that nanoporous titanium dioxide inverse opal structures fabricated using a self-assembled monolayer method and with enhanced infiltration of electron-donating polymers is an efficient electron-extracting layer, which enhances the photovoltaic performance. A calcination process generates an inverse opal structure of titanium dioxide (<70 nm of pore diameters) providing three-dimensional (3D) electron transport pathways. Hole-transporting polymers was successfully infiltrated into the pores of the surface-modified titanium dioxide under vacuum conditions at 200 °C. The resulting geometry expands the interfacial area between hole- and electron-transport materials, increasing the thickness of the active layer. The controlled polymer-coating process over titanium dioxide materials enhanced photocurrent of the solar cell device. Density functional theory calculations show improved interfacial adhesion between the self-assembled monolayer-modified surface and polymer molecules, supporting the experimental result of enhanced polymer infiltration into the voids. These results suggest that the 3D inverse opal structure of the surface-modified titanium dioxide can serve as a favorable electron-extracting layer in further enhancing optoelectronic performance based on organic or organic-inorganic hybrid solar cell.

Synthesis, characterization, and electrochemical properties of new highly processable, hole-transporting fluorocyclic aryl amine polymers

Perfluorocyclopentene (PFCP) aryl ether amine polymers demonstrate excellent solution processing into optically transparent, electrochemically active films as a potential hole-transporting layer material for organic electronic devices.

Utilization of “thiol–ene” photo cross-linkable hole-transporting polymers for solution-processed multilayer organic light-emitting diodes

Solution-processable hole-transporting layers (HTLs) capable of cross-linking are especially important in solution-processed organic light-emitting diodes (OLEDs) to achieve multilayer structures with separated charge-transporting layers and emitting layers. In this work, we report the first example of photo cross-linked HTL adopting “thiol–ene” reaction. A new allyl-containing hole-transporting polymer, Allyl-TFB, has been synthesized and characterized by NMR, TGA, DSC, UV-vis spectroscopy, cyclic voltammetry, etc. The allyl ether moiety successfully participated in thiol–ene photo cross-linking to give cross-linked HTL. The solvent resistance of the cross-linked Allyl-TFB film was evaluated by changing the UV irradiation time from 5 to 240 seconds. In addition to cross-linking, fine patterning of Allyl-TFB with a photo-mask was also demonstrated. To ascertain the usefulness of our new photo cross-linkable HTL system in phosphorescent OLEDs, OLED devices with the configuration of [ITO/PEDOT:PSS/(Allyl-TFB)/26DCzPPy:Ir(mppy)3/TPBi/CsF/Al] were fabricated. There were large differences in device characteristics depending upon the UV irradiation time of HTL, that is to say, the less UV irradiated (30 s) device, Device-1, showed lower operating voltage and higher efficiency than the more UV irradiated (180 s) one, Device-2. This difference in device characteristics originated from the difference in hole-transporting property with UV irradiation time, which was confirmed by hole-only device characterization. Device-1 also showed a better performance than the control device containing no HTL or simple TFB. The maximum luminous efficiency and power efficiency of Device-1 adopting our new cross-linked Allyl-TFB HTL were 31.4 cd A−1 and 21.8 lm W−1, respectively. Based on these results, we expect that this type of thiol–ene photo cross-linking will find various applications in cross-linking and patterning of active organic electronic materials as well as OLED materials.

Semiconducting Polymer Matrix as Charge Transport Materials and its Application in Polymer Electronic Devices

In the last decade, a number of intensive studies have been conducted to achieve efficient polymer light-emitting diodes (PLEDs). As a result of extensive multidisciplinary efforts, modern PLEDs offer substantial benefits over conventional cathode ray tubes (CRT) and liquid crystal displays (LCD). PLEDs display provides superior brightness and color purity, markedly lower power consumption, as well as full viewing angle without compromising image quality. Compared with small molecule organic LEDs (OLEDs), PLEDs use solution-based processes, which offer the potential for lower cost and roll-to roll processing on flexible substrates.An efficient PLED device typically consists of a stack of organic/polymeric thin layers, each of which performs a specific function aimed at improving the device performance or achieving the desired device functionality. In many cases, these layered structures are formed from the polymeric solution by spin-casting or printing with subsequent removal of the solvent carrier. However, solvent from the freshly deposited film frequently dissolve or partially dissolve the underlying layer, resulting in loss of the desired structure and corresponding device functionality. Undesirable changes in the morphology and interfaces of the polymer films are another detrimental effect associated with incompatible solvent and its removal.To make more robust hole transport layers (HTLs) and avoid solvent damage from subsequent emissive layer, the most common approach is to introduce polymerizable functional groups onto the base structure of the molecules with hole transporting (HT) property to form a cross-linkable HT molecules, which can form a cross-linked HTL upon treatment. However, such a type of polymerizable hole transport material is expensive and difficult to make, especially in large quantity.Herein we report a new approach to address this issue: Commercially available HT polymers are embedded into a crosslinked polymer network to &#x201C;lock&#x201D; uniformly distributed HT polymers inside the cross-linked polymer matrix. This approach proves to be more advantageous in terms of process simplicity and cost. Similarly, the same class of materials can potentially be employed in other polymer electronic devices, such as the organic photoconductor.An organic photoconductor commonly used in electrophotographic applications is a dual layer structure consisting of a thin (0.1um - 2 um) charge generation (CGL) bottom layer and a thick (about 20 um) charge transport (CTL) top layer. Light passes through the transparent CTL and strikes the CGL that generates free electrons and holes. Electrons are collected by the electrical ground of the photoreceptor and holes are driven towards to top of the CTL by an applied electrical field.CTL allows hole transport towards the surface, at which they are used to neutralize negative surface charges deposited during the pre-charging process. In essence, CTL consists of non-conductive organic material (usually polymer) with charge transport moieties embedded into it. We believe this semiconducting polymer matrix can act as charger transport materials for organic photoreceptor.

Electronic Structure Calculations for Hole-Transporting Triphenylamine Derivatives in Polymer Light-Emitting Diodes

Hole-transporting polymers based on polyethene-triphenylamine derivatives are investigated with respect to their UV/Vis spectra. Two substituents, N-phenyl-1-naphthylamine and carbazole, are examined as their respective polymer light-emitting diodes (PLEDs) show very different luminous efficiencies. In order to identify the origin of these phenomena electronic structure calculations based on TD-DFT were performed using monomer models of the hole-transporting polymers. In experiment these hole-transporting polymers show very specific differences in their absorption and emission (fluorescence and phosphorescence) spectra. The analysis of the simulated absorption and emission spectra, the MOs as well as the ground and excited state geometries give explanations for the different optical performances of the corresponding PLEDs.

Synthesis of Linear and Star-Shaped Poly[4-(diphenylamino)benzyl methacrylate]s by Group Transfer Polymerization and Their Electrical Memory Device Applications

Hole-transporting triphenylamine (TPA)-based polymers, the linear poly[4-(diphenylamino)benzyl methacrylate] (PTPMA) and the three-armed star-shaped poly[4-(diphenylamino)benzyl methacrylate] (N(PTPMA)3), have been synthesized by group transfer polymerization (GTP). For the synthesis of N(PTPMA)3, the core-first approach coupled with the GTP was adopted using a newly designed silyl ketene acetal initiator with three initiating points. The polymerization results showed that the polymer molecular weights were precisely controlled by the monomer/initiator ratio. The new hole-transporting TPA-based polymers could be blended with electron-accepting [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) for electrical memory device applications. The experimental results showed that pristine PTPMA and N(PTPMA)3 exhibited dynamic-random-access-memory (DRAM) volatile electrical behavior, but their PCBM composite-based devices changed to the write-once-read-many times (WORM) nonvolatile memory characteristic or conducto...

Polymers in Biomedicine and Electronics

The versatility of polymeric materials originates from the broad variety in their chemical structure and in their hierarchical organization as well as from the possibility to realize a wide spectrum of functions. Often such functions result from a combination ofamoleculararchitecture/morphology with a physical process and therefore require integration in a suitable system (e.g. medical device, electric circuit) or environment (e.g. physiological environment). Frequently, research in the area of functional polymers is motivated by applications. This special issue focuses on two application areas, in which polymer research as well as product development are progressing rapidly: Biomedicine and Electronics. Here (multi)functional polymers are an enabling technology and in this way create substantial and sustainable value. The significance of this topic is also highlighted at the conference ‘‘Polymers in Biomedicine and Electronics’’, which takes place from Oct 3 to 5, 2010 in Berlin combining the biannual meetings of the Gesellschaft Deutscher Chemiker (GDCh) Division ‘‘Macromolecular Chemistry’’ and of the Berlin-Brandenburgischer Verband fur Polymerforschung (BVP). Topics of the conference cover the design and the synthesis of functional polymers, physical principles underlying the function, the characterization of such functionswithin a system as well as product-oriented industrial research. Smart biomaterials, biocompatible coatings and their applications in controlled drug delivery systems or in regenerative therapies will be discussed in the biomedicine-oriented sessions of the conference. Photovoltaic, charge transport, light emission aswell as sensors andactuatorswill be subjects in the area of electronics.

Novel Non‐Conjugated Main‐Chain Hole‐Transporting Polymers for Organic Electronics Application

A new class of hole-transporting polymers for use in organic electronic devices such as organic light-emitting diodes (OLEDs) or photorefractive holographic storage devices has been synthesized. The polymers contain tetraarylbenzidines or tetraarylphenylenediamines as charge-transporting units in the polymer backbone and are connected by non-conjugating fluorene bridges. For use in OLEDs the novel polymers were functionalized with oxetane groups that can be cross-linked via a cationic ring opening polymerization to yield insoluble networks. Such insoluble films are necessary for the fabrication of multilayer devices by wet deposition techniques. The novel materials feature improved film-formation properties as demonstrated in green-emitting double-layer OLEDs.

Glass-forming hole-transporting carbazole-based hydrazone monomers, polymers, and twin compounds

Abstract The synthesis, optical, thermal, and photoelectrical properties of new carbazole-based hydrazone monomers, polymers, and twin compounds are reported. All the synthesized materials are capable of glass formation. Their glass transition temperatures range from 27 to 90 °C. The ionization potentials of the films of carbazole-based hydrazones measured by the electron photoemission technique range from 5.18 to 5.48 eV. Hole-drift mobilities in the amorphous films of the synthesized hydrazone monomers measured by the time-of-flight technique at room temperature reach 10 −4 cm 2 /(V s) at high applied electric fields.

Synthesis and photorefractivity of polysiloxanes bearing hole-conductors doped with a nonlinear optical chromophore

New polysiloxanes-based hole-transporting polymers have been synthesized and characterized. The polymer possesses an N-phenyl- N-propylphenanthren-9-amine ( PSX-PhPA) and 3-((2,2-diphenylhydrazone)methyl)-1-propyl- 1H-indole ( PSX-IDEH). Our results show that the photoconductivity, diffraction efficiency, and photorefractive response time were found to be 0.458 pS/cm, 54.9%, and 7.8 s for the PSX-PhPA composite and 1.044 pS/cm, 41.7%, and 5.47 s for the PSX-IDEH composite at wavelength of 633 nm.

Hole-transporting polymers containing carbazol-3,9-diyl and 1,4-phenylene fragments in the main chain

New carbazole-based polymers, which contain various content of electro-active fragments in the main chain connected via alkylene spacers, have been synthesized by Ni(0)-catalyzed Yamamoto-type aryl–aryl coupling reactions. These compounds represent amorphous materials of high thermal stability with glass-transition temperatures of 139–151 °C and thermal decomposition starting at temperatures above 400 °C. UV–vis absorption and photoluminescence emission spectra of the materials confirmed that the conjugated segments in the macromolecules are rather short. However, the polymers with varying content of the electro-active chromophores demonstrate different charge injection and transport properties in multilayer light emitting diodes with the polymers as the hole transport and tris(8-quinolinato)aluminium (Alq 3) as the electroluminescent/electron transport layer. The device based on the polymer containing bicarbazole segments in the main chain exhibits the best overall performance (turn-on voltage: 4 V; maximum photometric efficiency: 2.6 cd/A; maximum brightness: approximately 2200 cd/m 2).