Characterization of the charge transport and electrical properties in solution-processed semiconducting polymers

The conventional charge transport models based on density- and field-dependent mobility, only having a non-Arrhenius tem- perature dependence, cannot give good current-voltage characteristics of poly （2-methoxy-5-（2＇-ethylhexyloxy）-p-phenylene vinylene） （MEH-PPV） hole-only devices. In this paper, we demonstrate that the current-voltage characteristics can give a good unified description of the temperature, carrier density mad electric field dependence of mobility based on both the Arrhenius temperature dependence and the non-Arrhenius temperature dependence. Fu^hermore, we perform a systematic study of charge transport and electrical properties for MEH-PPV. It is shown that the boundary carrier density has an important effect on the current-voltage characteristics. Too large or too small values of boundary carrier density will lead to incorrect cur- rent-voltage characteristics. The numerically calculated carrier density is a decreasing function of the distance to the interface, and the numerically calculated electric field is an increasing function of the distance. Both the maximum of carrier density and the minimum of electric field appear near the interface.

SEMICONDUCTING AND METALLIC POLYMERS:THE FOURTH GENERATION OF POLYMERIC MATERIALS

INTRODUCTIONIn 1976, Alan MacDiarmid, Hideki Shirakawa and I, together with a talented group of graduate students andpost-doctoral researchers discovered conducting polymers and the ability to dope these polymers over the fullrange from insulator to metal. This was particularly exciting because it created a new field of research on theboundary between chemistry and condensed matter physics, and because it created a number of opportunities:

RBC Membrane Camouflaged Semiconducting Polymer Nanoparticles for Near-Infrared Photoacoustic Imaging and Photothermal Therapy

Semiconducting conjugated polymer nanoparticles(SPNs)represent an emerging class of phototheranostic materi-als with great promise for cancer treatment.In this report,low-bandgap electron donoracceptor(DA)-conjugated SPNs with sur-face cloaked by red blood cell membrane(RBCM)are developed for highly e ective photoacoustic imaging and photothermal therapy.The resulting RBCM-coated SPN(SPN@RBCM)displays remarkable near-infrared light absorption and good photosta-bility,as well as high photothermal conver-sion e ciency for photoacoustic imaging and photothermal therapy.Particularly,due to the small size(<5 nm),SPN@RBCM has the advantages of deep tumor penetration and rapid clearance from the body with no appreciable toxicity.The RBCM endows the SPNs with prolonged systematic circulation time,less reticuloendothelial system uptake and reduced immune-recognition,hence improving tumor accumulation after intravenous injection,which provides strong photoacoustic signals and exerts excellent photothermal therapeutic e ects.Thus,this work provides a valuable paradigm for safe and highly e cient tumor pho-toacoustic imaging and photothermal therapy for further clinical translation.

Modulating Bandgap and HOCO/LUCO Energy of Semiconducting Polymer by Copolymerization or Incorporation of Electron Withdrawing/Releasing Groups

The modulation of bandgap and HOCO/LUCO energies of conjugated polymers by copolymerization or by incorporation of electron withdrawing/releasing groups is studied.The study was conducted by band structure calculation applying density functional theory with generalized gradient approximation.The polymers and copolymers were modeled as 1D infinite system with periodical boundary condition along the molecular direction.It is concluded that the bandgap and HOCO/LUCO energies of conjugated polymers depend on both electron withdrawing/releasing effects and non-bonding interaction between a side group and the conjugated systems.

A Furan-Substituted Polymeric Hole-Transporting Material for Energy Level Regulation and Less Planarity in Colloidal Quantum Dot Solar Cells

For efficient colloidal quantum dot(CQD)solar cells(CQD-SCs),thiol-passivated p-type CQDs are generally used as a hole-transporting material(HTM);however,there are issues with the control of optoelectrical properties,low thiol passivation rate,and poor morphology with a power conversion efficiency(PCE)of approximately 11%.Although polymeric HTMs have been introduced to address these issues,maximizing efficiency and achieving green-solvent processability and thermal stability for commercialization is necessary.Here,we synthesize a novel benzodifuran(BDF)-based HTM(asy-ranPBTBDF)showing an electron-deficient state,low steric hindrance,and low planarity compared to those of a typical benzodithiophene(BDT)-based HTM(asy-ranPBTBDT).BDF properties lead to deep high occupied molecular orbital(HOMO)levels,closeπ-πstacking,excellent solubility,and amorphous properties related to efficiency,green-solvent processability,and thermal stability.With these benefits,the asy-ranPBTBDF-based CQD-SC showed enhanced open-circuit voltage(Voc)(0.65 V)and PCE(13.29%)compared to those of the asy-ranPBTBDT-based device(0.63 V and 12.22%)in toxic processes with chlorobenzene.The asy-ranPBTBDF-based CQD-SC showed a PCE of 12.51%in a green-solvent process with 2-methylanisole and improved thermal stability at 80℃(83.8%retaining after 24 h)owing to less lateral crystallization than the asy-ranPBTBDT-based device(60.8%retaining after 24 h).

Rational design of biodegradable semiconducting polymer nanoparticles for NIR-II fluorescence imaging-guided photodynamic therapy

Semiconducting polymer nanoparticles(SPNs)have shown great promise in second near-infrared window(NIR-II)phototheranostics.However,the issue of long metabolic time significantly restricts the clinical application of SPNs.In this study,we rationally designed a biodegradable SPN(BSPN50)for NIR-II fluorescence imaging-guided photodynamic therapy(PDT).BSPN50 is prepared by encapsulating a biodegradable SP(BSP50)with an amphiphilic copolymer F-127.BSP50 is composed of NIR-II fluorescent diketopyrrolopyrrole(DPP)segment and degradable poly(phenylenevinylene)(PPV)segment with the ratio of 50/50.BSPN50 has both satisfactory degradability under myeloperoxidase(MPO)/hydrogen peroxide(H_(2)O_(2))and NIR-II fluorescence emission upon 808 nm laser excitation.Furthermore,BSPN50 shows good photodynamic efficacy under 808 nm laser irradiation.BSPN50 shows a faster degradation rate than BSPN100 which has no PPV segment both in vitro and in vivo.In addition,BSPN50 can effectively diagnose tumor via NIR-II fluorescence imaging and inhibit the tumor growth by PDT.Thus,our study provides a rational approach to construct biodegradable nanoplatforms for efficient tumor NIR-II phototheranostics.

Controlling Ion Conductance and Channels to Achieve Synapticlike Frequency Selectivity

Enhancing ion conductance and controlling transport pathway in organic electrolyte could be used to modulate ionic kinetics to handle signals. In a Pt/Poly(3-hexylthiophene-2,5-diyl)/Polyethylene?Li CF3SO3/Pt hetero-junction, the electrolyte layer handled at high temperature showed nano-fiber microstructures accompanied with greatly improved salt solubility. Ions with high mobility were confined in the nano-fibrous channels leading to the semiconducting polymer layer,which is favorable for modulating dynamic doping at the semiconducting polymer/electrolyte interface by pulse frequency.Such a device realized synaptic-like frequency selectivity, i.e., depression at low frequency stimulation but potentiation at high-frequency stimulation.

High-photosensitivity polymer thin-film transistors based on poly(3-hexylthiophene)

Polymer thin-film transistors （PTFTs） based on poly（3-hexylthiophene） are fabricated by the spin-coating process, and their photo-sensing characteristics are investigated under steady-state visible-light illumination. The photosensitivity of the device is strongly modulated by gate voltage under various illuminations. When the device is in the subthreshold operating mode, a significant increase in its drain current is observed with a maximum photosensitivity of 1.7×10^3 at an illumination intensity of 1200 lx, and even with a relatively high photosensitivity of 611 at a low illumination intensity of 100 lx. However, when the device is in the on-state operating mode, the photosensitivity is very low： only 1.88 at an illumination intensity of 1200 lx for a gate voltage of -20 V and a drain voltage of -20 V. The results indicate that the devices could be used as photo-detectors or sensors in the range of visible light. The modulation mechanism of the photosensitivity in the PTFT is discussed in detail.

A"donor–acceptor"structured semiconductor polymer for near infrared fluorescence imaging guided photodynamic therapy

Near infrared(NIR)fluorescence imaging guided photodynamic therapy(PDT)is a technique which has been developed in many clinical trials due to its advantage of real-time optical monitoring,specific spatiotemporal selectivity,and minimal invasiveness.For this,photosensitizers with NIR fluorescence emission and high^(1)O_(2)generation quantum yield are highly desirable.Herein,we designed and synthesized a"donor-acceptor"(D-A)structured semiconductor polymer(SP),which was then wrapped with an amphiphilic compound(Pluronic■F127)to prepare water-soluble nanoparticles(F-SP NPs).The obtained F-SP NPs exhibit good water solubility,excellent particle size stability,strong absorbance at deep red region,and strong NIR fluorescent emission characteristics.The maximal mass extinction coe±cient and fluorescence quantum yield of these F-SPs were calculated to be 21.7 L/(g·cm)and 6.5%,respectively.Moreover,the^(1)O_(2)quantum yield of 89%for F-SP NPs has been achieved under 635 nm laser irradiation,which is higher than Methylene Blue,Ce6,and PpIX.The outstanding properties of these F-SP NPs originate from their unique D-A molecular characteristic.This work should help guide the design of novel semiconductor polymer for NIR fluorescent imaging guided PDT applications.

Electronic mobility in the high-carrier-density limit of ion gel gated IDTBT thin film transistors

Indacenodithiophene-co-benzothiadiazole（IDTBT） has emerged as one of the most exciting semiconducting polymers in recent years because of its high electronic mobility and charge transport along the polymer backbone. By using the recently developed ion gel gating technique we studied the charge transport of IDTBT at carrier densities up to 10^21cm^-3.While the conductivity in IDTBT was found to be enhanced by nearly six orders of magnitude by ionic gating, the charge transport in IDTBT was found to remain 3D Mott variable range hopping even down to the lowest temperature of our measurements, 12 K. The maximum mobility was found to be around 0.2 cm^2·V^-1·s^-1, lower than that of Cytop gated field effect transistors reported previously. We attribute the lower mobility to the additional disorder induced by the ionic gating.

Gadolinium-containing semiconducting polymer nanoparticles for magnetic resonance/fluorescence dual-modal imaging and photothermal therapy of oral squamous cell carcinoma

Oral squamous cell carcinoma(OSCC)is the most common malignant tumor of the oral and maxillofacial region.Due to its unique location,earlier and more accurate diagnosis and more minimally invasive treatment of OSCC is of major importance.Herein,gadolinium-containing semiconductor polymer nanoparticles(SPN-Gd)were designed and prepared.The nanoparticles consist of a near-infrared(NIR)absorption semiconductor polymer(PCPDTBT)served as fluorescence signal source and a photothermal conversion agent(PTA)and a gadolinium-grafted triblock amphiphilic copolymer(F127-DTPA-Gd)served as a magnetic resonance imaging(MRI)contrast agent and nanocarrier.The experiments in vivo showed that SPN-Gd could act as an MRI contrast agent and optical image agent with a long retention time,and it had a significant inhibiting effect on tumors of OSCC mice model through photothermal therapy(PTT).Thus our study provides a simple nanotheranostic platform composed of two components for efficient MR/fluorescence dual-modal imaging-guided PTT.

Nanoscale engineering of conducting polymers for emerging applications in soft electronics

Soft electronics featuring exceptional mechanical compliance and excellent electrical performance hold great promise for applications in soft robotics,artificial intelligence,bio-integrated electronics,and wearable electronics.Intrinsically stretchable and conductive materials are crucial for soft electronics,enabling large-area and scalable fabrication,high device density,and good mechanical compliance.Conducting polymers are inherently stretchable and conductive.They can be precisely synthesized from vastly available building blocks,and thus they provide a fruitful platform for fabricating soft electronics.However,amorphous bulk-phase conducting polymers typically exhibit poor mechanical and electrical characteristics.Consequently,it is highly desirable to develop novel engineering approaches to overcome the intrinsic limitations of conducting polymers.In recent years,numerous engineering strategies have been developed to enhance their performances in soft electronic devices via constructing various nanostructures.In this review,we first summarize several unique methodologies to fabricate conducting polymer-based nanostructures.We then discuss how nanoscale engineering approaches can improve several crucial parameters,including electrical conductivity,stretchability,sensitivity,and self-healing property of conducting polymers.Moreover,we also discuss device-level integration of conducting polymer-based nanostructures with other materials for applications in skin-inspired electronics and bio-integrated electronics.Finally,we provide perspectives on challenges and future directions in engineering nanostructured conducting polymers for soft electronics.

New Semiconducting Polymer Based on Benzo[1,2-b：4,5-bldiselenophene Donor and Diketopyrrolopyrrole/Isoindigo Acceptor Unit： Synthesis, Characterization and Photovoltaics

Two new D-A type polymers PBDSe-DPP and PBDSe-ID were synthesized to explore new ideal semiconduct- ing polymers, by conjugating acceptor unit diketopyrrolopyrrole/isoindigo to a donor unit benzo[l,2-b：4,5-b＇]di- selenophene, which is designed by substituting the sulfur atom with a selenium atom in the benzo[1,2-b：4,5-b＇]- dithiophene. The thermal, optical, electrochemical, photoelectric and photovoltaie properties of the two polymers were studied systematically. Relatively high open circuit voltage （0.7 and 0.75 V） and fill factor （〉65%） were demonstrated for both polymers. Huge increase （by 64% and 120%） of the short circuit current density was achieved for both polymer based devices by using additive compared to the corresponding reference without addi- tive, resulting in decent power conversion efficiency of 3.7% and 2.5% respectively with only simple optimizing consideration. We believe this class of BDSe polymer possesses a good potential to be alternatives of active material for photovoltaic applications.

Poly-N-benzylaniline prepared in perchloric acid——a new soluble semiconducting polymer

Chemical or electrochemical oxidation of N-benzylaniline in perehloric acid solution yields a highly colored polymer——poly-N-benzylaniline (PBAn).The polymer has good solubility in a num- ber of organic solvents in either acid or base form.At room temperature,conductivity measurements on pressed pellets of the acid form PBAn give a conductivity of 9.3×10^(-6) S·cm^(-1).The soluble polymer was analyzed using a variety of common experimental techniques including UV-vis,IR,NMR,ESR spectroscopy,elemental analysis and electrochemieal analysis.All experimental results showed that PBAn has a structure similar to polyaniline with the elimination of some benzyl groups.

非共价键构象锁策略优化半导体聚合物纳米颗粒的NIR-Ⅱ光声/光热性能用于高效光诊疗

开发近红外二区(NIR-Ⅱ)响应的纳米制剂用于NIR-Ⅱ光声成像(PAI)引导的光热治疗(PTT)为推进深层组织光诊疗的发展提供了机遇.尽管半导体聚合物纳米颗粒(SPNs)在NIR-ⅡPAI和PTT中展现出巨大的应用潜力,但其有限的光声/光热效能使得实现高效的体内光诊疗仍然是一个巨大的挑战.本工作中,我们提出了一种基于非共价键构象锁(NCL)的分子工程策略来优化SPN的NIR-Ⅱ光声/光热性能,以实现高效的体内光诊疗.NCL的引入有助于改善半导体聚合物主链的平面性,增强其捕光能力,从而提高NIR-Ⅱ光声/光热信号的输出.优化出的SPN3毒性低、尺寸合适、光物理性能好,不仅能被4T1癌细胞有效摄取并在NIR-Ⅱ光激发下杀死细胞,而且经全身给药后可通过NIR-ⅡPAI点亮肿瘤轮廓,进一步指导NIR-ⅡPTT的进行以实现高效的肿瘤热消融.因此本文的研究提供了一种独特的分子设计策略来放大SPN的NIR-Ⅱ光声/光热信号,最终实现活体高效光诊疗.

Effect of Molecular Weight and Processing Additive on the Performance of Low Bandgap Polymer Solar Cells

In this work, we synthesized a low bandgap polymer polysilole（-2,6-diyl-alt-5-octylthieno[3,4-c]pyrrole-4,6- dione） （PDTSTPD） with different molecular weights （Mn）. The devices based on PDTSTPD/PC71BM composite are prepared and the dependence of power conversion efficiency （PCE） of the devices on the M,1 of conjugated poly- mers is addressed. We found the hole mobility of PDTSTPD is dependent on the Mn of the polymer, which should be the main reason contributing to the drastic difference of device performance, i.e. the PCE of the device using 10 kDa polymer is only 0.52%, in contrast to 2.3% for 24 kDa polymer device. This PCE data is then further improved to 5.0% via using 1,8-diiodoctane as processing additive to achieve an optimized morphology for the photoactive layer with an appropriate length-scale of phase separation for both exciton dissociation and charge transportation.

NIR-IIb excitable bright polymer dots with deep-red emission for in vivo through-skull three-photon fluorescence bioimaging

It is of great significance to study the brain structure and function in deep-tissue for neuroscience research and bio-medical applications because of the urgent demand for precise theranostics.Three-photon fluorescence microscopic(3PFM)bioimaging excited by the light in near-infrared IIb(NIR-IIb,1,500–1,700 nm)spectral region is one of the most promising imaging techniques with the advantages of high spatial resolution,large imaging depth,and reduced scattering.Herein,a type of NIR-IIb light excitable deep-red emissive semiconducting polymer dots(P-dots)with bright 3PF and large three-photon absorption cross-section(σ3)at 1,550 nm was prepared.Then the P-dots were functionalized with polystyrene polymer polystyrene graft ethylene oxide functionalized with carboxyl groups(PS-PEG-COOH)and modified with NH2-poly(ethylene glycol)(PEG)to synthesis photochemically stable and biocompatible P-dots nanoparticles(NPs).Further the P-dots NPs were utilized for in vivo 3PFM bioimaging of cerebral vasculature with and without the brain skull under 1,550 nm femtosecond(fs)laser excitation.In vivo 3PFM bioimaging of the mice cerebral vasculature at various vertical depths was obtained.Moreover,a vivid three-dimensional structure of the mice vascular architecture beneath the skull was reconstructed.At the depth of 350μm beneath the brain skull,3.8μm blood vessels could still be clearly recognized.NIR-IIb excitable P-dots assisted 3PFM bioimaging has great potential in accurate deep tissue bioimaging.

Morphological and mechanical characterization of a PMMA/CdS nanocomposite

Thickfilm of poly(methyl methacrylate)(PMMA)/CdS nanocomposite have been synthesized by the solution casting process.The nanostructure of the CdS particles has been ascertained through the small angle X-ray scattering(SAXS)technique.The surface morpholo-gical characterization of the PMMA/CdS nanocomposite has been done through scanning electron microscopy(SEM)analysis.The variation of mechanical loss factor(Tanδ)with temperature and tensile properties of prepared samples have been studied using Dynamic Mechanical Analyzer(DMA).This study reveals that the glass transition temperature(Tg),Young’s modulus,and fracture energy of the PMMA/CdS nanocomposite are greatly influenced by the existence of interfacial energetic interaction between dispersed CdS nanoparticles and the matrix of PMMA.

Multi-Stimuli-Responsive Field-Effect Transistor with Conjugated Polymer Entailing Spiropyran in the Side Chains

Multi-stimuli-responsive field-effect transistors(FETs)with organic/polymeric semiconductors have received increasing attention.Herein,we report a novel strategy for fabricating multi-stimuliresponsive polymeric semiconductors through the incorporation of spiropyran(SP)groups in the polymer side chains.The semiconducting performances of resultant FETs with a diketopyrrolopyrroles(DPP)-based conjugated donor–acceptor(D–A)polymer,that entails SP units in the side chains(pDSP-1),could be modulated reversibly through UV and visible light irradiations,or UV light irradiation and heating,or acid treatment and heating.Our studies reveal that during the reversible transformations of closed,open,and the protonated forms of spiropyran,achieved by light irradiations,heating,and under acidic conditions,a large dipole moment changes occur,which triggers the reversible variation of semiconducting performance of the FETs.

Template‑Assisted Fabrication of Single‑Crystal‑Like Polymer Fibers for Efficient Charge Transport

Polymer semiconductors with highly crystalline forms,such as crystalline nanowires and fibers,are critical for charge carrier transport in organic field-effect transistors(OFET).However,the highly crystalline form usually requires high-quality molecular orderliness,which still remains a great challenge,especially in single fibers of extremely high-molecular-weight semiconducting polymers.In this study,we present an anodic aluminum oxide(AAO)template-assisted method to fabricate highly crystalline N-alkyl diketopyrrolopyrrole dithienylthieno[3,2-b]thiophene(DPP-DTT)single fibers.Grazing-incidence X-ray diffraction and selected area electron diffraction show obvious diffraction patterns for single-crystal-like characteristics,indicating the highly ordered molecular chains and highly crystalline structures of the single DPP-DTT fibers.OFET based on the single-crystal-like DPP-DTT fiber exhibits the highest charge carrier mobility of up to 14.2 cm^(2)V^(−1)s^(-1)and an average mobility of approximately 7.8 cm^(2)V^(−1)s^(-1),which is significantly improved compared with DPP-DTT thin film-based devices.Besides,the fiber-based OFET also exhibit a high light responsivity of 4.0.103 A W^(−1).This work demonstrates a facile and effective method for fabricating single-crystal-like fibers of high-molecular-weight polymer semiconductors and corresponding high-performance OFET devices.Furthermore,it also expands application of AAO template method for achieving crystalline semiconducting polymer fibers and provide a new perspective for the study on polymer crystallization.