Two environmentally and thermally stable [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives, BOP-BTBT and DBOP-BTBT are successfully synthesized and analyzed as active layers in organic thin film transistors. The effects of methoxy on BTBT based OTFT materials are reported for the first time. The experimental results show an excellent optimization influence of methoxy group on the OTFT performance with an improved hole transport mobility up to 0.63 cm2 V−1 s−1 (BOP-BTBT) and 3.57 cm2 V−1 s−1 (DBOP-BTBT). Meantime the mono- and bis-substituted derivatives are compared in terms of their physical properties and device performance. We find that the threshold voltage decreases when more methoxy groups are introduced.

•Super hydrophobic deep blue OLED fluorescence materials is a new concept.•Introduced super hydrophobic groups achieved better moisture resistant properties ,and deeper blue simultaneously.•Astonishing performance is envisioned by molecular design based on theoretical calculations and the single crystal X-Ray.•The CIE value for new materials are exactly match with the High-Definition Television requirements for deep blue emission.Fluorescent deep-blue emitters consisting of arylamine chrysene have attracted immense commercial interest in organic light-emitting devices (OLEDs). Herein, we endeavor to design emitters with super hydrophobic groups, namely trifluoromethoxy (OCF3) or trifluoromethylsufanyl (SCF3) substituted on 6,12-diarylamine chrysene. Surprisingly, the new materials show highly efficient and substantial blue shift in fluorescence spectra with more pure color quality, higher thermostability and better moisture resistant properties. Astonishing electroluminescence performance is envisioned by promoting the molecular design based on experience and theoretical calculations along with the single crystal X-Ray analysis. The CIE coordinate values for 6, 12-diamine-N,N,N′,N′-tetra(p-trifluoromethoxyphenyl)chrysene (DATPC-OCF3) and 6,12-diamine-N,N,N′,N′-tetra(p-trifluoromethylsulfanylphenyl)chrysene (DATPC-SCF3) are (0.14, 0.09) and (0.15, 0.06), respectively, which exactly match with the National Television System Committee (NTSC) and High-Definition Television requirements for unprecedented deep-blue emission.Download high-res image (208KB)Download full-size image

•A novel alcohol-soluble carboxylic potassium salt (F-R-COOK) is introduced as an alternative cathode buffer layer (CBL) in inverted perovskite solar cells.•F-R-COOK enhanced PCE 14.37% compared to the PCE 9.51% of the Ag-only device.•Potential candidate as electrode modification layer in inverted perovskite solar cells.Using a novel solution-processed carboxylic potassium salt (F-R-COOK) as cathode buffer layer (CBL), a power conversion efficiency (PCE) of 14.37% is obtained, which is more than 51% increase compared with that of the Ag-only device under similar fabrication conditions. The test result of single electron devices and Electrochemical impedance spectroscopy (EIS) measurements demonstrate that the interlayer decreases charge transport resistance. Ultraviolet photoelectron spectroscopy (UPS) measurements are used to study the interfacial effects induced by the new CBL. It is found that F-R-COOK can reduce the work function of the Ag electrode by forming desired interfacial dipoles. Our work indicates the promising applications of F-R-COOK based CBL in perovskite solar cells and may provide some insights into the design and synthesis of new interfacial materials to further improve the device performance.Download high-res image (304KB)Download full-size image

AbstractA novel geometry for electroluminescent devices, which does not require transparent electrodes for electrical input, is demonstrated, theoretically analyzed, and experimentally characterized. Instead of emitting light through a conventional electrode, light emission occurs through a polar liquid or solid and input electrical electrodes are coplanar, rather than stacked in a sandwich configuration. This new device concept is scalable and easily deployed for a range of modular alternating-current-powered electroluminescent light sources and light-emitting sensing devices. The polar-electrode-bridged electroluminescent displays can be used as remotely readable, spatially responsive sensors that emit light in response to the accumulation and distribution of materials on the device surface. Using this device structure, various types of alternating current devices are demonstrated. These include an umbrella that automatically lights up when it rains, a display that emits light from regions touched by human fingers (or painted upon using a mixture of oil and water), and a sensor that lights up differently in different areas to indicate the presence of water and its freezing. This study extends the dual-stack, coplanar-electrode device geometry to provide displays that emit light from a figure drawn on an electroluminescent panel using a graphite pencil.

AbstractBright and stable blue emitters with narrow full-width at half-maxima are particularly desirable for applications in television displays and related technologies. Here, this study shows that doping aluminum (Al3+) ion into CsPbBr3 nanocrystals (NCs) using AlBr3 can afford lead-halide perovskites NCs with stable blue photoluminescence. First, theoretical and experimental analyses reveal that the extended band gap and quantum confinement effect of elongated shape give rise to the desirable blueshifted emission. Second, the aluminum ion incorporation path is rationalized qualitatively by invoking fundamental considerations about binding relations in AlBr3 and its dimer. Finally, the absence of anion-exchange effect is corroborated when green CsPbBr3 and blue Al:CsPbBr3 NCs are mixed. Combinations of the above two NCs with red-emitting CdSe@ZnS NCs result in UV-pumped white light-emitting diodes (LED) with an National Television System Committee (NTSC) value of 116% and ITU-R Recommendation B.T. 2020 (Rec. 2020) of 87%. The color coordinates of the white LED are optimized at (0.32, 0.34) in CIE 1931. The results suggest that low-cost, earth-abundant, solution-processable Al-doped perovskite NCs can be promising candidate materials for blue down-conversion layer in backlit displays.

AbstractOrganic semiconductor materials with high charge-carrier mobility and high luminescence are promising for fabricating high-performance organic light-emitting transistors and electrically pumped organic laser diodes. Some derivatives with an anthracene core show both characteristics; however, independently controlling the size and the thickness of single-crystal films is challenging. Here, 2D and 3D crystal formation is demonstrated by using an air-stable organic semiconductor, 2,6-bis[4-ethylphenyl]anthracene (BEPAnt). The shape of the single-crystal films can be changed from about 0.10 mm in diameter and 400 nm in thickness to 1.0 mm in diameter and 50 nm in thickness by controlling the growth conditions using saturation–supersaturation vapor pressure curves. The in-plane growth rate increases by ten times while the out-of-plane growth rate decreases to about 1/8 as the growth temperature increases from 210 to 250 °C. Single-crystal organic field-effect transistors based on BEPAnt show isotropic mobilities as high as 7.2 cm2 V−1 s−1.

2,6-Dihalogen atom substituted-9,10-anthraquinones are used as organic cathode materials for rechargeable lithium ion batteries. The differences in the cyclic voltammetry curves, voltage profiles and cycling performance of these compounds are analyzed. An important regularity is strikingly found: the lighter the density of a material, the easier is the achievement of the material’s theoretical capacity at the first scanning cycle. This finding gives an understanding to improve the practical specific capacity of lithium battery and a very clear direction to design new compounds in future so as to make full use of the theoretical capacities.Download high-res image (102KB)Download full-size image

•The structure-property relationship of fused-ring electron acceptors is briefly discussed.•The principle of molecular design is presented.•A novel non-fullerene acceptor material DNIT-TT2T is designed and synthesized.•OSCs based on P3HT:DNIT-TT2T are investigated, exhibiting high Voc.In this work, the structure-property relationship of fused-ring electron acceptors is briefly discussed and the principle of molecular design is presented. Based on this principle, perylene diimide (PDI) was cracked by inserting thiophene and thieno[3,2-b]thiophene (TT) to design and synthesize a novel A-D-A (acceptor-donor-acceptor) small molecule DNIT-TT2T, which served as a non-fullerene acceptor material in our fabricated organic solar cells (OSCs). DNIT-TT2T shows excellent thermal stability, it possesses a broad absorption by covering the wavelength range of 300–600 nm and relatively high LUMO energy level of −3.75 eV, which is close to the theoretically calculated value. The power conversion efficiency (PCE) of OSCs based on the blend of P3HT donor and DNIT-TT2T acceptor (1:1, w/w) is found to be 1.25%, with a high open-circuit voltage (Voc) of 0.88 V, indicating that 1,8-naphthalimide (NI) based molecules are promising acceptors for non-fullerene polymer solar cells and excellent photovoltaic properties can be achieved by rationally designing the molecules.Download high-res image (253KB)Download full-size image

Two novel thieno[3,2-b]thiophene (TT)/3,4-ethylenedioxythiophene (EDOT)-based compounds of 2,5-(EDOT–TT–EDOT) type bearing electron-withdrawing side groups (4-cyanophenyl or 4-pyridyl) at 3,6-positions of the TT moiety have been synthesized. Their electropolymerization leads to electroactive conjugated polymers, P(CNPh-ETTE) and P(Py-ETTE), which possess electrochromic properties changing the color from purple to pale grey-blue or from sand brown to pale grey-green, respectively. Cyclic voltammetry and spectroelectrochemical experiments reveal that functionalization with electron-withdrawing side groups decreases the HOMO and LUMO energy levels and contracts the band gap of materials. Both new polymers demonstrated extremely short response times of 0.9–1.1 s for bleaching and 0.34–0.35 s for coloring. P(CNPh-ETTE) and P(Py-ETTE) polymers showed reasonably good contrast (16–23%) and coloration efficiency (120–190 cm2 C−1) in the visible region (at the maxima of their π–π* transitions, 540/570 nm), and high contrast and coloration efficiency in the near-infrared region (50–62% and 324–440 cm2 C−1 at 1500 nm, respectively). While the stability of the pyridine-functionalized polymer, P(Py-ETTE), was shown to be low (with unstable charge–discharge characteristics, presumably due to the protonation of the pyridine ring during the redox process), P(CNPh-ETTE) demonstrated superior electrochromic performance retaining 91–96% of its electroactivity after 2000 cycles between −0.5 and +1.0 V. DFT calculations on these and related EDOT–TT–EDOT polymers reported by us early have been presented and analyzed to understand the structure–property relationships in this class of electrochromic polymers.

A couple of novel electrochromic materials poly(2,3,4,5-tetrakis(2,3-hydrothieno[3,4-b]dixin-5-yl)-1-methyl-1H-pyrrole) (P(t-EDOT-mPy)) and poly(5,5′,5′′,5′′′-(thiophene-2,3,4,5-tetrayl)tetrakis(2,3-dihydrothieno[3,4-b][1,4]dioxine)) (P(t-EDOT-Th)) are electrodeposited via multi-position polymerization of their tetra-EDOT substituted monomers t-EDOT-mPy and t-EDOT-Th, respectively. Compared with the linear 2D structured poly(thiophene) (Eg=2.2 eV) and poly(2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)thiophene) (Eg=1.7 eV), P(t-EDOT-Th) (Eg=1.62 eV) has the lowest band gap. Hence, we speculate that the band gaps of the two polymers, having 3D structures, are decreased in contrast to non-substituted polymers or bi-EDOT substituted polymers, thiophene and 1-methyl-1H-pyrrole. The results indicated that P(t-EDOT-Th) thin films are more stable and show higher transmittance amid two polymers, which may find their utilization in organic optoelectronics.

Thieno[3,2-b]thiophene (TT) monomers end-capped with 3,4-ethylenedioxythiophene (EDOT) moieties are electropolymerized to form π-conjugated polymers with distinct electrochromic (EC) properties. Steric and electronic factors (electron donor and acceptor substituents) in the side groups of the TT core, as well as the structure of the polymer backbone strongly affect the electrochemical and optical properties of the polymers and their electrochromic characteristics. The studied polymers show low oxidation potentials, tunable from–0.78 to +0.30 V (vs. Fc/Fc+) and the band gaps from 1.46 to 1.92 eV and demonstrate wide variety of color palettes in polymer films in different states, finely tunable by structural variations in the polymer backbone and the side chains. EC materials of different colors in their doped/dedoped states have been developed (violet, deep blue, light blue, green, brown, purple-red, pinkish-red, orange-red, light gray, cyan and colorless transparent). High optical contrast (up to 79%), short response time (0.57–0.80 s), good cycling stability (up to 91% at 2000 cycles) and high coloration efficiency (up to 234.6 cm2 C–1) have been demonstrated and the influence of different factors on the above parameters of EC polymers have been discussed.

In-plane isotropic charge transport in single crystals is desirable in large-area single-crystal thin-film transistor (FET) arrays because it is independent of crystal direction. However, most organic semiconductors show anisotropic charge transport, while only a few show isotropic or moderately isotropic charge transport characteristics. We report a highly isotropic charge transport semiconductor material, 2,6-bis(4-methoxyphenyl)anthracene (BOPAnt), and demonstrate BOPAnt-based single-crystal FETs with a high mobility of 13–16 cm2 V−1 s−1 and an anisotropic mobility ratio (μmax/μmin) of approximately 1.23, the lowest value yet reported. Using the single-crystal structure of BOPAnt, the rectangular diffraction patterns of the molecular lattice parameters in single-crystal thin films were analysed by transmission electron microscopy and polarized optical microscopy. The highly isotropic properties are attributed to the molecular structure enhancement by incorporation of methoxyphenyl units; our analysis revealed an orthorhombic lattice arrangement in the solid state, with the molecules packed in an unusual fashion in this particular stacking mode. In addition, hole mobility calculations combining the transfer integrals and the reorganization energy are used to explain the charge-transport properties.

Tetracene, one of the polyacene derivatives, shows eminent optical and electronic properties with relatively high stability. To take advantage of the intrinsic properties of the tetracene molecule and explore new semiconductors, herein, we report the design and synthesis of two novel p-channel tetracene derivatives, 2-(4-dodecyl-phenyl)-tetracene (C12-Ph-TET) and 2-phenyl-tetracene (Ph-TET). Top contact OTFTs were fabricated using these two materials as semiconductor layers, with charge mobilities up to 1.80 cm2 V−1 s−1 and 1.08 cm2 V−1 s−1, respectively. Our molecular modeling results indicate that the introduction of phenyl into tetracene can improve the efficient charge transport in electronic devices as a result of the increased electronic coupling between the two neighboring planes of the molecules. AFM images of the thermally evaporated thin films of these two materials show large grains, which correspond to the high mobilities of these devices. Consequently, the mobility of our OTFTs based on C12-Ph-TET is the highest for OTFTs based on tetracene derivatives reported to date. The single crystal analyses show the existence of π–π stacking interactions within the molecules with the introduction of mono-phenyl substituents, which is the main cause of the increased mobility. The impressive properties of these two materials indicate that the introduction of alkyl-phenyl and phenyl group could be an excellent method to improve the properties of the organic semiconductor materials.

Herein, thin film and single crystal phototransistors based on 2,6-bis(4-methoxyphenyl)anthracene (BOPAnt) are systematically studied. High quality BOPAnt single crystals are grown via the PVT (physical vapor transport) method to fabricate bottom gate top contact phototransistors. The thin film phototransistor shows a photoresponsivity of 9.75 A W−1 under 1 mW cm−2 blue LED illumination, whereas under the same conditions the single crystal based phototransistor displays a photoresponsivity of 414 A W−1. Furthermore, using low power monochromatic light with the wavelength of 350 nm, the photoresponsivity of 3100 A W−1 under 0.11 mW cm−2 illumination and EQE of 9.5 × 105% are obtained for the BOPAnt single crystal phototransistor with the channel length of 65 μm. The much higher photoresponsivity of the single crystal based phototransistor is due to its much higher exciton diffusion length compared to that of the thin film device, which is also evident by the large Von shift towards the positive voltage direction. The photoswitching behaviors of the single crystal based phototransistor are also studied. It is observed that after a short warming up period, the single crystal based phototransistor shows stable switching behavior.

One of the most striking features of organic semiconductors compared with their corresponding inorganic counterparts is their molecular diversity. The major challenge in organic semiconductor material technology is creating molecular structural motifs to develop multifunctional materials in order to achieve the desired functionalities yet to optimize the specific device performance. Azo-compounds, because of their special photoresponsive property, have attracted extensive interest in photonic and optoelectronic applications; if incorporated wisely in the organic semiconductor groups, they can be innovatively utilized in advanced smart electronic applications, where thermal and photo modulation is applied to tune the electronic properties. On the basis of this aspiration, a novel azo-functionalized liquid crystal semiconductor material, (E)-1-(4-(anthracen-2-yl)phenyl)-2-(4-(decyloxy)phenyl)diazene (APDPD), is designed and synthesized for application in organic thin-film transistors (OTFTs). The UV–vis spectra of APDPD exhibit reversible photoisomerizaton upon photoexcitation, and the thin films of APDPD show a long-range orientational order based on its liquid crystal phase. The performance of OTFTs based on this material as well as the effects of thermal treatment and UV-irradiation on mobility are investigated. The molecular structure, stability of the material, and morphology of the thin films are characterized by thermal gravimetric analysis (TGA), polarizing optical microscopy (POM), (differential scanning calorimetry (DSC), UV–vis spectroscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). This study reveals that our new material has the potential to be applied in optical sensors, memories, logic circuits, and functional switches.Keywords: anthracene; azo-compound; liquid crystal; organic thin-film transistors; photoresponsive;

A novel exciplex-forming host is applied so as to design highly simplified reddish orange light-emitting diodes (OLEDs) with low driving voltage, high efficiency, and an extraordinarily low efficiency roll-off, by combining N,N-10-triphenyl-10H-spiro [acridine-9,9′-fluoren]-3′-amine (SAFDPA) with 4,7-diphenyl-1,10-phenanthroline (Bphen) doped with trivalent iridium complex bis(2-methyldibenzo[f,h]quinoxaline) (acetylacetonate)iridium(III) (Ir(MDQ)2(acac)). The reddish orange OLEDs achieve a strikingly high power efficiency (PE) of 31.80 lm/W with an ultralow threshold voltage of 2.24 V which is almost equal to the triplet energy level of the phosphorescent reddish orange emitting dopant. The power efficiency of the device with the exciplex-forming host is enhanced, achieving 36.2% mainly owing to the lower operating voltage by the novel exciplex forming cohost, compared with the reference device (23.54 lm/W). Moreover, the OLEDs show extraordinarily low current efficiency (CE) roll-off to 1.41% at the brightness from 500 to 5000 cd/m2 with a maximal CE of 32.87 cd/A (EQEmax = 11.01%). The devices display a good reddish orange color (CIE of (0.628, 0.372) at 500 cd/m2) nearly without color shift with increasing brightness. Co-host architecture phosphorescent OLEDs show a simpler device structure, lower working voltage, and a better efficiency and stability than those of the reference devices without the cohost architecture, which helps to simplify the OLED structure, lower the cost, and popularize OLED technology.Keywords: efficiency roll-off; exciplex-forming host; hole-transport-material-free; OLED; reddish orange phosphorescence;

In inverted planar heterojunction (PHJ) perovskite solar cells (PSCs), the interface layer between the electron transporting layer and the cathode plays a very important role in achieving high power efficiency. Herein, we present the synthesis of a new water/alcohol soluble small molecular cationic compound based on the naphthalene diimide functionalized pyridinium salt, N,N′-bis(1-n-hexylpyridinium-4-ylmethyl)-1,4,5,8-naphthalenetetracarboxydiimide (PN6). PN6 exhibits a large band gap (2.95 eV), high electron mobility (7.1 × 10−5 cm2 V−1 s−1), deep LUMO energy level (−4.07 eV) and can easily form highly transparent thin films. By introducing it as a cathode interface layer in PHJ PSCs, PN6 can effectively decrease the work function of the cathode, boosting all the photovoltaic parameters of the fabricated devices. By using PN6 in the ITO/NiOx/perovskite/PC61BM/PN6/Ag device structure, a power conversion efficiency (PCE) of 17.27% is obtained. Moreover, it is observed that the performance of PHJ PSCs with the PN6 interface layer is insensitive to the interlayer thickness and even at a thickness of 30 nm; the PCE of the device can still reach up to 15.37%, which makes it compatible with large-area roll-to-roll processing technology. These results demonstrate that the naphthalene diimide functionalized pyridinium salt can be a new category of water/alcohol soluble cathode interface material for high performance PHJ PSCs.

During the past few years, two-dimensional (2D) layered materials have emerged as the most fundamental building blocks of a wide variety of optoelectronic devices. The weak van der Waals (vdW) interlayer forces allow the 2D monolayers to isolate and restack into arbitrary stacking heterojunctions. The recently developed chemical vapor deposition (CVD) technique shows great promise for the production of large domain building blocks of 2D heterostructures with vertical and lateral stacking and much better device performance. This review is the first of its kind to discuss the research progress of flexible FETs based on graphene/semiconductor heterostructures, in which graphene acts as both electrode and semiconductor material.

Three new spirofluorene-based hole transport materials, Spiro-S, Spiro-N, and Spiro-E, are synthesized by replacing the para-methoxy substituent in 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-MeOTAD) with methylsulfanyl, N,N-dimethylamino and ethyl groups. Their properties as hole transport materials in perovskite solar cells are investigated. The impact of replacing the para-methoxy substituent on bulk properties, such as the photophysical properties, HOMO/LUMO energy level, hole extraction properties and morphologies of perovskite thin films are investigated. Their optoelectronic and charge-transport properties and performance in perovskite solar cells are compared with the current benchmarked and structurally-related hole transport material (HTM) Spiro-MeOTAD. Surprisingly, the methylsulfanyl substituted spirofluorene shows the highest power conversion efficiency of 15.92% among the investigated spirofluorenes, which is an over 38% increase in PCE compared with that of Spiro-MeOTAD under similar device fabrication conditions.

N,N′-Bis(4-trifluoromethoxyphenyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide (NDI-POCF3) and N,N′-bis(4-trifluoromethoxybenzyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide (NDI-BOCF3) have similar optical and electrochemical properties with a deep LUMO level of approximately 4.2 eV, but exhibit significant differences in electron mobility and molecular packing. NDI-POCF3 exhibits nondetectable charge mobility. Interestingly, NDI-BOCF3 shows air-stable electron transfer performance with enhanced mobility by increasing the deposition temperature onto the octadecyltrichlorosilane (OTS)-modified SiO2/Si substrates and achieves electron mobility as high as 0.7 cm2 V–1 s–1 in air. The different mobilities of those two materials can be explained by several factors including thin-film morphology and crystallinity. In contrast to the poor thin-film morphology and crystallinity of NDI-POCF3, NDI-BOCF3 exhibits larger grain sizes and improved crystallinities due to the higher deposition temperature. In addition, the theoretical calculated transfer integrals of the intermolecular lowest unoccupied molecular orbital (LUMO) of the two materials further show that a large intermolecular orbital overlap of NDI-BOCF3 can transfer electron more efficiently than NDI-POCF3 in thin-film transistors. On the basis of fact that the theoretical calculations are consistent with the experimental results, it can be concluded that the p-(trifluoromethoxy) benzyl (BOCF3) molecular architecture on the former position of the naphthalene tetracarboxylic diimides (NDI) core provides a more effective way to enhance the intermolecular electron transfer property than the p-(trifluoromethoxy) phenyl (POCF3) group for the future design of NDI-related air-stable n-channel semiconductor.

A series of three polymers based on a thieno[3,2-b]thiophene core is synthesized and polymerized via electrochemical polymerization. The addition of benzene and thiophene rings as two different types of substituents on the 3,6-position of the thieno[3,2-b]thiophene core brings about a variance in color changing, optical contrast and morphological demeanor. Electrochromical studies demonstrate that P1 and P2 switch between deep blue neutral and colorless transparent oxidized states, while P3 switches between violet and light green transmissive states. Amid the three polymers, P1 shows the highest optical contrast (71%) in the visible region with complete coloring and bleaching in just 1.10 s and 1.80 s, respectively. In addition, all three polymers reveal about 60% of the transmittance change in the near-IR region, which endows them with commendable applications in NIR electrochromic devices. AFM images depict an augmented surface roughness due to the introduction of alkyl chains in the thieno[3,2-b]thiophene core, which gives rise to a better stability of the polymer thin film.

Two thieno[3,2-b]thiophene based polymers (poly[2,5-bis(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)thieno[3,2-b]thiophene] (P(2,5-BTE)) and poly[3,6-bis-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)thieno[3,2-b]thiophene] (P(3,6-BTE))) were synthesized by an electrochemical method. By alternating the 3,4-ethylenedioxythiophene (EDOT) position along the polymer backbone we studied the electrochemical and optical properties by comparing the 2,5- and 3,6-positions on the thieno[3,2-b]thiophene unit. The theoretically calculated bandgaps and ultraviolet-visible spectrum peaks of the two dimers are in good agreement with the polar energy and peak range in the ultraviolet-visible and near-infrared (UV-Vis-NIR) spectrum, which helps us to comprehend the process of electrochemical polymerization and indicates that P(2,5-BTE) has a more conjugated structure than P(3,6-BTE). With the increase in voltage, both of the polymers gradually transform to their quinoid structures. Effective color tuning by changing the position of the EDOT units is the noteworthy property of P(2,5-BTE) and P(3,6-BTE), which makes them suitable electrochromic materials.

•The non-doped EML is economical and promising for OLEDs due to easy fabrication and low reagent consumption process.•We report a novel wide color-range tunable and low efficiency roll-off fluorescent OLED using two undoped ultrathin EML.•The CT-OLEDs are tunable from cold white to warm white with CCT 6932 K and 3072 K, respectively.We demonstrated a novel wide color-range tunable, highly efficient and low efficiency roll-off fluorescent organic light-emitting diode (OLED) using two undoped ultrathin emitters having complementary colors and an interlayer between them. The OLED can be tuned to emit sky blue (0.22, 0.30), cold white (0.29, 0.33), warm white (0.43, 0.42) and yellow (0.40, 0.45) according to the Commission Internationale de L’Eclairage (CIE) 1931 (x, y) chromaticity diagram. The device fabrication was simplified by eliminating doping process in the emission layers. The influence of interlayer thickness on luminous efficiency, efficiency roll-off and color tuning mechanism is thoroughly studied. The recombination zone is greatly broadened in the optimized device, which contributes to stable energy transfer to both emitters and suppressed concentration quenching. With a threshold voltage of 2.82 V, the color tunable organic light emitting diode (CT-OLED) shows a maximum luminance of 39,810 cd/m2, a peak external quantum efficiency (EQE) 6% and the efficiency roll-off as low as 11.1% at the luminance from 500 cd/m2 to 5000 cd/m2. This structure of CT-OLED has great advantages of easy fabrication and low reagent consumption. The fabricated CT-OLEDs are tunable from cold white (0.30, 0.36) to warm white (0.43, 0.42) with correlated color temperature (CCT) 6932 K and 3072 K, respectively, demonstrating that our proposed approach helps to meet the need for lighting with various CCTs.

In the quest to develop novel solution-processable neutral green electrochromic polymers, the donor–acceptor (D–A) polymer PBOTT-BTD has been synthesized through direct C–H arylation polycondensation, using 3,6-bis(hexyloxy)thieno[3,2-b]thiophene instead of conventional D units and benzo[c][1,2,5]thiadiazole as the A unit. PBOTT-BTD films obtained through spray-coating were investigated systematically; this green polymer turned blue in the oxidized state, realizing a conversion between two primary colors. PBOTT-BTD exhibited rapid response times, desirable contrasts in both the visible and near-infrared (NIR) regions, favorable efficiencies, and reasonable optical memory and stability, making it a promising candidate for use as a new green electrochromic conjugated polymer. Accordingly, PBOTT-BTD might have applicability not only as an electrochromic material but also in NIR or optical memory devices, perhaps even in supercapacitor applications; the use of thieno[3,2-b]thiophene units presenting alkoxy groups might also allow the preparation of novel D–A conjugated polymers when matched with various acceptor units.

Tetracene, one of the polyacene derivatives, shows eminent optical and electronic properties with relatively high stability. To take advantage of the intrinsic properties of the tetracene molecule and explore new semiconductors, herein, we report the design and synthesis of two novel p-channel tetracene derivatives, 2-(4-dodecyl-phenyl)-tetracene (C12-Ph-TET) and 2-phenyl-tetracene (Ph-TET). Top contact OTFTs were fabricated using these two materials as semiconductor layers, with charge mobilities up to 1.80 cm2 V−1 s−1 and 1.08 cm2 V−1 s−1, respectively. Our molecular modeling results indicate that the introduction of phenyl into tetracene can improve the efficient charge transport in electronic devices as a result of the increased electronic coupling between the two neighboring planes of the molecules. AFM images of the thermally evaporated thin films of these two materials show large grains, which correspond to the high mobilities of these devices. Consequently, the mobility of our OTFTs based on C12-Ph-TET is the highest for OTFTs based on tetracene derivatives reported to date. The single crystal analyses show the existence of π–π stacking interactions within the molecules with the introduction of mono-phenyl substituents, which is the main cause of the increased mobility. The impressive properties of these two materials indicate that the introduction of alkyl-phenyl and phenyl group could be an excellent method to improve the properties of the organic semiconductor materials.

A smart polymer is developed by in situ fabrication of polyacrylamide hydrogel with polyiodide. The resulting PAM hydrogel doped with polyiodide showed a high sensitivity to temperature and humidity. Its special humidity-response behavior with high responsivity makes the described hydrogel a highly promising material for building temperature- and humidity-control switches.

Herein, thin film and single crystal phototransistors based on 2,6-bis(4-methoxyphenyl)anthracene (BOPAnt) are systematically studied. High quality BOPAnt single crystals are grown via the PVT (physical vapor transport) method to fabricate bottom gate top contact phototransistors. The thin film phototransistor shows a photoresponsivity of 9.75 A W−1 under 1 mW cm−2 blue LED illumination, whereas under the same conditions the single crystal based phototransistor displays a photoresponsivity of 414 A W−1. Furthermore, using low power monochromatic light with the wavelength of 350 nm, the photoresponsivity of 3100 A W−1 under 0.11 mW cm−2 illumination and EQE of 9.5 × 105% are obtained for the BOPAnt single crystal phototransistor with the channel length of 65 μm. The much higher photoresponsivity of the single crystal based phototransistor is due to its much higher exciton diffusion length compared to that of the thin film device, which is also evident by the large Von shift towards the positive voltage direction. The photoswitching behaviors of the single crystal based phototransistor are also studied. It is observed that after a short warming up period, the single crystal based phototransistor shows stable switching behavior.

Three new spirofluorene-based hole transport materials, Spiro-S, Spiro-N, and Spiro-E, are synthesized by replacing the para-methoxy substituent in 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-MeOTAD) with methylsulfanyl, N,N-dimethylamino and ethyl groups. Their properties as hole transport materials in perovskite solar cells are investigated. The impact of replacing the para-methoxy substituent on bulk properties, such as the photophysical properties, HOMO/LUMO energy level, hole extraction properties and morphologies of perovskite thin films are investigated. Their optoelectronic and charge-transport properties and performance in perovskite solar cells are compared with the current benchmarked and structurally-related hole transport material (HTM) Spiro-MeOTAD. Surprisingly, the methylsulfanyl substituted spirofluorene shows the highest power conversion efficiency of 15.92% among the investigated spirofluorenes, which is an over 38% increase in PCE compared with that of Spiro-MeOTAD under similar device fabrication conditions.

In-plane isotropic charge transport in single crystals is desirable in large-area single-crystal thin-film transistor (FET) arrays because it is independent of crystal direction. However, most organic semiconductors show anisotropic charge transport, while only a few show isotropic or moderately isotropic charge transport characteristics. We report a highly isotropic charge transport semiconductor material, 2,6-bis(4-methoxyphenyl)anthracene (BOPAnt), and demonstrate BOPAnt-based single-crystal FETs with a high mobility of 13–16 cm2 V−1 s−1 and an anisotropic mobility ratio (μmax/μmin) of approximately 1.23, the lowest value yet reported. Using the single-crystal structure of BOPAnt, the rectangular diffraction patterns of the molecular lattice parameters in single-crystal thin films were analysed by transmission electron microscopy and polarized optical microscopy. The highly isotropic properties are attributed to the molecular structure enhancement by incorporation of methoxyphenyl units; our analysis revealed an orthorhombic lattice arrangement in the solid state, with the molecules packed in an unusual fashion in this particular stacking mode. In addition, hole mobility calculations combining the transfer integrals and the reorganization energy are used to explain the charge-transport properties.

In inverted planar heterojunction (PHJ) perovskite solar cells (PSCs), the interface layer between the electron transporting layer and the cathode plays a very important role in achieving high power efficiency. Herein, we present the synthesis of a new water/alcohol soluble small molecular cationic compound based on the naphthalene diimide functionalized pyridinium salt, N,N′-bis(1-n-hexylpyridinium-4-ylmethyl)-1,4,5,8-naphthalenetetracarboxydiimide (PN6). PN6 exhibits a large band gap (2.95 eV), high electron mobility (7.1 × 10−5 cm2 V−1 s−1), deep LUMO energy level (−4.07 eV) and can easily form highly transparent thin films. By introducing it as a cathode interface layer in PHJ PSCs, PN6 can effectively decrease the work function of the cathode, boosting all the photovoltaic parameters of the fabricated devices. By using PN6 in the ITO/NiOx/perovskite/PC61BM/PN6/Ag device structure, a power conversion efficiency (PCE) of 17.27% is obtained. Moreover, it is observed that the performance of PHJ PSCs with the PN6 interface layer is insensitive to the interlayer thickness and even at a thickness of 30 nm; the PCE of the device can still reach up to 15.37%, which makes it compatible with large-area roll-to-roll processing technology. These results demonstrate that the naphthalene diimide functionalized pyridinium salt can be a new category of water/alcohol soluble cathode interface material for high performance PHJ PSCs.