New materials based on carbazole for optoelectronic device applications：Theoretical investigation

A quantum-chemical investigation on the structural and optoelectronic properties of two materials based on carbazole is carried out.The purpose is to display the effect of grafting the fluorine atoms on their optoelectronic and physico-chemical properties.In addition to solubility in the polar solvents and the modification in geometric parameters,the substitution of fluorine destabilizes the HOMO and LUMO levels,decreases the band gap energy and raises conjugation length.These properties suggest the substituted fluorine compound as a good candidate for optoelectronic applications.     

Recent progress in functionalized electrophosphorescent iridium(Ⅲ) complexes

Iridium(Ⅲ) complexes are one of the most important electrophosphorescent dyes with tunable emissions in the range of visible and near infrared lights,high photoluminescence yields and short lifetimes for high-efficiency organic light-emitting diodes(OLED) with 100% exciton harvesting.This review summarizes the recent development of electroluminescent Ir~(3+) complexes functionalized with host-featured carrier-transporting groups,with emphasis on correlations between functionalization,optoelectronic properties and device performance.According to the introducing approaches,the complexes were sorted with conjugated and aliphatic linkages,as well as the types of functional groups.The modification effect on physical properties and the state-of-the-art device performances were discussed.     

Triarylborane π-electron systems with intramolecular charge-transfer transitions

The incorporation of B element into π-conjugated system is an efficient strategy to tune the steric and electronic structure and thus optoelectronic properties of π-electron systems.The vacant p orbital on the tricoordinate B center makes it exhibit several electronic and steric features,such as electron-accepting ability through p-π~* conjugation,the high Lewis acidity to coordinate with Lewis bases,as well as the steric bulk arising from the aryl substituent on the B center to get enough kinetic stability.As a result,the boryl group is a very unique electron acceptor.When an electron-donating amino group is present,the triarylboranes would display intense intramolecular charge transfer transitions,which lead to interesting optoelectronic properties and great utilities.This short review summarizes the recent progress in π-electron systems,which contain both B and N elements and thus display intramolecular charge-transfer transitions.The triarylboranes are introduced based on their structural features,including the linear π-system with boryl and amino groups at the terminal positions,the lateral borylsubstituted π-system with amino groups at the terminal positions,the biphenyl π-system with an amino and a boryl groups at o,o'-positions,nonconjugated U- and V-shaped π-system,macrocylcic π-system with B and N embedded in the ring,B,N-bridged ladder-type π-system,as well as the polycyclicπ-system with B embedded in the center.     

A solution-processed nanoscale COF-like material towards optoelectronic applications

Two-dimensional(2 D)covalent organic frameworks(COFs)with periodic functionalπ-electron systems are an emerging class of optoelectronic materials.However,almost all conjugated COFs so far are insoluble and hard to process,which hampers severely their optoelectronic applications.Here,a solution-processable,nanoscale and sp2 carbon-conjugated COF-like material,PDPP-C20 was successfully designed and synthesized.The solution-processed PDPP-C20 films exhibit high crystallinity and excellent charge transport properties along out-of-plane directions,combined with the highest occupied molecular orbital(HOMO)/lowest unoccupied molecular orbital(LUMO)levels of-5.36/-3.75 e V,making PDPP-C20 suitable for electronic device applications.An efficiency as high as 21.92%has been demonstrated when it was used as a functional interfacial layer in perovskite solar cells,coupled with dramatically improved stability in comparison with the control device due to the superior hydrophobicity of PDPP-C20 layer as well as its passivation effect on perovskite surface.Furthermore,the soluble PDPP-C20 could also be used as donor in bulk-heterojunction organic solar cells and an initial efficiency of 2.46%has been achieved.These results indicate that this new class of soluble and nanoscale COF-like materials should offer a new arena of functional materials for optoelectronic devices.     

Zinc Stannate Nanostructures for Energy Conversion

To date,ternary metal oxide semiconductor materials have attracted extensive attention worldwide due to their unique optoelectronic properties.As a classical ternary oxide,Zn2SnO4 is featured with the high electron mobility,wide band gap,negligible visible light absorption and tailorable electronic band structures.Thus,it is an ideal material for practical use in solar cells,lithium batteries,sensors,and photo-catalysts.In this review,we summarize the recent research progress of this material with the focus on the synthesis methods,nanostructures,and the resulting effects on the crystal structure,optical properties,and photoelectrochemical properties.Moreover,their potential applications in different devices are highlighted and carefully discussed.     

Current advancements on charge selective contact interfacial layers and electrodes in flexible hybrid perovskite photovoltaics

Perovskite-based photovoltaic materials have been attracting attention for their strikingly improved performance at converting sunlight into electricity.The beneficial and unique optoelectronic characteristics of perovskite structures enable researchers to achieve an incredibly remarkable power conversion efficiency.Flexible hybrid perovskite photovoltaics promise emerging applications in a myriad of optoelectronic and wearable/portable device applications owing to their inherent intriguing physicochemical and photophysical properties which enabled researchers to take forward advanced research in this growing field.Flexible perovskite photovoltaics have attracted significant attention owing to their fascinating material properties with combined merits of high efficiency,light-weight,flexibility,semitransparency,compatibility towards roll-to-roll printing,and large-area mass-scale production.Flexible perovskite-based solar cells comprise of 4 key components that include a flexible substrate,semi-transparent bottom contact electrode,perovskite(light absorber layer)and charge transport(electron/hole)layers and top(usually metal)electrode.Among these components,interfacial layers and contact electrodes play a pivotal role in influencing the overall photovoltaic performance.In this comprehensive review article,we focus on the current developments and latest progress achieved in perovskite photovoltaics concerning the charge selective transport layers/electrodes toward the fabrication of highly stable,efficient flexible devices.As a concluding remark,we briefly summarize the highlights of the review article and make recommendations for future outlook and investigation with perspectives on the perovskite-based optoelectronic functional devices that can be potentially utilized in smart wearable and portable devices.     

Nondilute 1,2-dichloroethane solution of poly(9,9-dioctylfluorene-2,7-diyl): A study on the aggregation process

Molecular aggregates in conjugated polymer(CP) solution can propagate into mesoscale morphology of the relevant film and further dominate the optoelectronic property. Herein, we probed the aggregation behavior of poly(9,9-dioctylfluorene-2,7-diyl)(PFO) and studied its influence on the photophysical property in 1,2-dichloroethane(DCE) solution, where the contents of β-phase or-aggregates increased with prolonged aging time. Thereinto, high quality β-film was fabricated from DCE solution with critical aggregate time of 6 min. The film exhibited excellent surface morphology and characteristic emission of β-phase. Meanwhile, films prepared from aged DCE solutions exhibited high crystallinity, which was promising to obtain higher photoluminance efficiency and charge transport ability simultaneously. Therefore, it is significant to get deep insight into the aggregation behavior of CP, which is involved not only with the solution-processing technology of plastic device, but also with the optoelectronic property of CP.     

π-CONJUGATED OLIGOMERS IN SUPRAMOLECULAR CRYSTALS AND THEIR OPTOELECTRONIC FUNCTIONS

Functional organic molecular materials and conjugated oligomers or polymers now allow the low-cost fabrication of thin films for insertion into new generations of electronic and optoelectronic devices. The performance of these devices relies on the understanding and optimization of several complementary processes. Our goal is to discuss the relationship between the molecular stacking structures and their optoelectronic properties that are of importance in all these areas. The concept of intermolecular interaction should be taken here in the special sense that is inter-dipole coupling. Specifically, we will address the impact of inter-dipole interaction between adjacent molecules in aggregate state on the solid-state emission properties.     

A Novel Synthesis of Two-dimensional Nanopatterned TiO2 Thin Film

Recently the research on structures with an ordered two-dimensional(2D) pattern has attracted great attention due to its versatile applications in the fields of microelectronic and optoelectronic devices, displays, biochips and sensors, enzymatic immobilization, drug carriers, and photonic band gap materials. Various well-arrayed 2D structures have been made by the modern technique such as laser writing pattern fabrication, photoetching technique, micro-electromechanical systems based on scann…     

Progress on the optoelectronic functional organic crystals

Organic crystals constructed by pi-conjugated molecules have been paid great attention to in the field of organic optoelectronic materials. The superiorities of these organic crystal materials, such as high thermal stability, highly ordered structure, and high carrier mobility over the amorphous thin film ma-terials, make them attractive candidates for optoelectronic devices. Single crystal with definite struc-ture provides a model to investigate the basic interactions between the molecules (supramolecular interaction), and the relationship between molecular stacking modes and optoelectronic performance (luminescence and carrier mobility). Through modulating molecular arrangement in organic crystal, the luminescence efficiency of organic crystal has exceeded 80% and carrier mobility has been up to the level of 10 cm2·V?1·s?1. Amplified stimulated emission phenomena have been observed in many crys-tals. In this paper, we will emphatically introduce the progress in optoelectronic functional organic crystals and some correlative principle.     

Dipole and charge effects of chloroaluminum phthalocyanine revealed by local work function measurements at sub-molecular level

Chloroaluminum phthalocyanine (ClAlPc), an important optoelectronic molecule with a permanent dipole moment pointing from the Pc ring to the ending Cl atom, adsorbed on Au(111) in either Cl-up or Cl-down configuration. Scanning tunneling microscopy/spectroscopy measurements revealed that at the centers of Cl-up and Cl-down molecules, the local work functions changed oppositely with respect to the Au(111) substrate. At their Pc lobes, however, the local work functions unanimously increased due to charging effect of the indole lobes in the ClAlPc molecule.     

Noncovalent conformational locks in organic semiconductors

Highly planar conformation is considered to be one of the most important properties for high performance organic semiconductors. Among all kinds strategies for designing highly performing materials, noncovalent conformational locks(NCLs)have been widely used to increase the planarity and rigidity for π-conjugated systems. This review summarizes π-conjugated small molecules and polymers by employing various NCLs for controlling molecular conformation in the past two years. The optoelectronic properties of the conjugated materials, together with their applications on organic field-effect transistors(OFETs)and organic photovoltaics(OPVs) are discussed. Besides, the outlook and challenges in this field are also presented. It is obvious that NCLs play an important role in the design and synthesis of high-performance organic semiconductors.     

PURIFIED POLAR POLYFLUORENE FOR LIGHT-EMITTING DIODES AND LIGHT-EMITTING ELECTROCHEMICAL CELLS

Conjugated ployfluorene with 2-(2-(2-methoxyethoxy)ethoxy)ethyl groups(EO-PF)is prepared by the palladiumcatalyzed Suzuki coupling reaction.The polymer is purified carefully by a simple chemical procedure.The inductively coupled plasma(ICP)test shows palladium-catalyst in the polymer can be removed by this procedure.The thermal properties,electrochemical properties,UV-Vis absorption properties,photoluminescence properties and electroluminescent properties of the polymer without(EO-PF1)or with purification(EO-PF2)are studied.EO-PF2 shows better PL CIE coordinates in THF solutions as blue light-emitting materials and better photoluminescence stability in thin solid films. Polymer light emitting diodes and electrochemical cells based on EO-PF2 exhibit somewhat improved optoelectronic performance than control devices of EO-PF1.     

Characterization of self-assembled monolayers of porphyrins bearing multiple-thiol and photoelectric response

Self-assembled monolayers(SAMs) of thiol-derivatized porphyrin molecules on Au substrate have attracted extensively interest for use in sensing,optoelectronic devices and molecular electronics.In this paper,tetra-[p-(3-mercaptopropyloxy)-phenyl]porphyrin was synthesized and self-assembled with thiol on Au substrate for porphyrin SAMs(PPS 4).The electrochemical results demonstrated that PPS 4 could form excellent SAMs on gold surface.Self-assembled nanojunctions of PPS 4 were fabricated by using gold nanogap electrodes(gap width:ca.100 nm).With the light on/off,the nanojunctions showed current high/low as nanometer scaled photo switch.     

Single-wall carbon nanotube-containing cathode interfacial materials for high performance organic solar cells

Water/alcohol soluble cathode interfacial materials(CIMs)are playing important roles in optoelectronic devices such as organic light emitting diodes,perovskite solar cells and organic solar cells(OSCs).Herein,n-doped solution-processable single-wall carbon nanotubes(SWCNTs)-containing CIMs for OSCs are developed by dispersing SWCNTs to the typical CIMs perylene diimide(PDI)derivatives PDIN and PDINO.The Raman and X-ray photoelectron spectroscopy(XPS)measurement results illustrate the ndoped behavior of SWCNTs by PDIN/PDINO in the blend CIMs.The blended and n-doped SWCNTs can tune the work function and enhance the conductivity of the PDI-derivative/SWCNT(PDI-CNT)composite CIMs,and the composite CIMs can regulate and down-shift the work function of cathode,reduce the charge recombination,improve the charge extraction rate and enhance photovoltaic performance of the OSCs.High power conversion efficiency(PCE)of 17.1%and 17.7%are obtained for the OSCs based on PM6:Y6 and ternary PM6:Y6:PC₇₁ BM respectively with the PDI-CNTcomposites CIMs.These results indicate that the ndoped SWCNT-containing composites,like other n-doped nanomaterials such as zero dimensional fullerenes and two dimensional graphenes,are excellent CIMs for OSCs and could find potential applications in other optoelectronic devices.     

Plasmonic CsPbBr3–Au nanocomposite for excitation wavelength dependent photocatalytic CO2 reduction

The optoelectronic performance of CsPbBr_3 nanocrystal(NC) has been dramatically limited by the severe charge carrier recombination and its narrow light absorption range,which are anticipated to be resolved via coupling with plasmonic Au nanoparticle(NP).In view of this,CsPbBr_3-Au nanocomposite is fabricated and further employed as a concept model to study the electronic interaction between perovskite NC and Au NP for the first time.It has been found that the excitation-wavelength dependent carrier transfer behavior exists in CsPbBr_3-Au nanocomposite.Upon illumination with visible light(λ>420 nm),photo-generated electrons in CsPbBr_3 can inject into Au with an electron injection rate and efficiency of 2.84×10~9 s^-1 and 78%,respectively.The boosted charge separation is further translated into a 3.2-fold enhancement in CO_2 photocatalytic reduction activity compared with pristine CsPbBr_3.On the other hand,when solely exciting Au NP with longer wavelength light(λ>580 nm),the localized surface plasmon resonance(LSPR) induced hot electrons in Au NPs can transfer to CsPbBr_3 NC and further participate in photocatalytic reaction towards CO_2 reduction.The present study provides new insights into preparing plasmonic nanostructure to enhance the performance of perovskite based optoelectronic devices.     

Aggregation-induced phosphorescence and mechanochromic luminescence of a tetraphenylethene-based gold(Ⅰ) isocyanide complex

In this study,a new twisting gold(Ⅰ) isocyanide complex based on tetraphenylethene(TPE),TPE-NC-Au.was designed and synthesized.It exhibits aggregation induced phosphorescence(AIP) characteristics,owing to the incorporation of Au moiety and conformation rigidification in the aggregated states.Moreover,the emission color of the crystalline solid of TPE-NC-Au changes from blue(454 nm) to green(500 nm) in response to mechanical grinding,due to the combined effects of conformation planarization,enhanced π…π stacking,as well as the emergence of aurophilic interactions in the ground amorphous state.Notably,the emission color can be restored upon solvent fuming,associating with the reconstruction of crystalline lattices.The AIP and switchable mechanochromism of TPE-NC-Au make it suitable for potential applications in bioimaging,sensing,and optoelectronic devices.     

New tetraphenylpyridinium-based luminogens with aggregation-induced emission characteristics

The research on aggregation-induced emission (AIE) has drawn increasing interests in the past decade. With the efforts scientists paid, a variety of AIE systems have been developed, among which the tetraphenylethelene and silole derivatives are the most studied. Development of new AIE systems could further enrich the AIE molecules and promote the development of AIE area. In this communication, we prepared a new AIE system based on 1,2,4,6-tetraphenylpyridinium ions according to the restriction of intramolecular rotation mechanism. These molecules could be facilely synthesized via one-step and one-pot reaction. The ionic AIE-active molecules could find wide application in sensing and optoelectronic areas.     

Efficient and stable planar all-inorganic perovskite solar cells based on high-quality CsPbBr3 films with controllable morphology

All-inorganic cesium lead bromide(CsPbBr3)perovskite is attracting growing interest as functional materials in photovoltaics and other optoelectronic devices due to its superb stability.However,the fabrication of high-quality CsPbBr3 films still remains a big challenge by solution-process because of the low solubility of the cesium precursor in common solvents.Herein,we report a facile solution-processed approach to prepare high-quality CsPbBr3 perovskite films via a two-step spin-coating method,in which the Cs Br methanol/H2 O mixed solvent solution is spin-coated onto the lead bromide films,followed by an isopropanol-assisted post-treatment to regulate the crystallization process and to control the film morphology.In this fashion,dense and uniform CsPbBr3 films are obtained consisting of large crystalline domains with sizes up to microns and low defect density.The effectiveness of the resulting CsPbBr3 films is further examined in perovskite solar cells(PSCs)with a simplified planar architecture of fluorine–doped tin oxide/compact Ti O2/CsPbBr3/carbon,which deliver a maximum power conversion efficiency of 8.11%together with excellent thermal and humidity stability.The present work offers a simple and effective strategy in fabrication of high-quality CsPbBr3 films for efficient and stable PSCs as well as other optoelectronic devices.     

A one-pot method for controlled synthesis and selective etching of organic-inorganic hybrid perovskite crystals

Organometal halide perovskites have recently emerged with a huge potential for photovoltaic applications. Moreover, preparation of high-quality perovskite crystals with controlled morphology is of great significance for the fundamental studies such as optical and electrical properties, as well as the applications. Here, we report a one-pot solvothermal process to synthesize sheet-shaped CH_3NH_3PbBr_3 single crystals with the lateral size of 100 μm and the thickness of 3–8 μm. Furthermore, a controlled etching behavior on the crystalline surface was demonstrated, which could be the irregular collapse of the crystalline surface caused by the local accumulation of methylammonium cations. Using this technique,CH_3NH_3PbBr_3 single crystal sheets could be used in the various optoelectronic devices, such as nanolaser,optical sensors, photodetectors and field effect transistors.