Amplification of circularly polarized luminescence (CPL) is demonstrated in a triplet–triplet annihilation-based photon upconversion (TTA-UC) system. When chiral binaphthyldiamine acceptors are sensitized with an achiral Pt(II) octaethylporphine (PtOEP) in solution, upconverted circularly polarized luminescence (UC-CPL) were observed for the first time, in which the positive or negative circularly polarized emission could be obtained respectively, following the molecular chirality of the acceptors (R/S). More interestingly, one order of magnitude amplification of the dissymmetry factor glum in UC-CPL was obtained in comparison with the normal promoted CPL. The multistep photophysical process of TTA-UC including triplet–triplet energy transfer (TTET) and triplet–triplet annihilation (TTA) have been suggested to enhance the UC-CPL, which provided a new strategy to design CPL materials with a higher dissymmetry factor.

•Two asymmetric blue-green emitting materials based on t-APE were firstly designed and synthesized.•These two materials possess high thermal stability, morphological durability, and bipolar characteristics.•The blue-green and white OLEDs based on these two materials show preferable performance.1-(9-Anthryl)-2-phenylethene (t-APE) is a blue-green material with high fluorescence quantum yield (Фf 0.44). However, it is easily crystallized. Herein, Two asymmetric blue-green emitting materials based on t-APE, (E)-9-(4-(2-(anthracen-9-yl)vinyl)phenyl)-10-(naphthalen-1-yl)anthracene (6) and (E)-9-(4-(2-(anthracen-9-yl)vinyl)phenyl)-10-(naphthalen-2-yl)anthracene (7) were firstly designed and synthesized. The two compounds possess high thermal stability, morphological durability, and bipolar characteristics. The non-doped blue-green organic light-emitting diodes (OLEDs) using 6 and 7 as emitting layers showed emission at 495 nm, full width at half maximum of 80 nm, maximum brightness of 13,814, 10,579 cd m−2, maximum current efficiency of 3.62, 7.16 cd A−1, and Commission Internationale de L'Eclairage (CIE) coordinate of (0.20, 0.43), respectively. Furthermore, when employing 6 and 7 as blue-green emitting layers and rubrene doped in tris-(8-hydroxyquinolinato)aluminum (Alq3) as the orange emitting layers to fabricate white OLEDs (WOLEDs), the WOLEDs exhibit a maximum brightness of 10,984, 14,652 cd m−2, maximum current efficiency of 2.04, 2.70 cd A−1, and CIE coordinate of (0.30, 0.40), (0.37, 0.47), Color Rendering Index (CRI) of 65, 60, stable EL spectra, respectively. This study demonstrates that the t-APE-type derivatives have the excellent properties for the emitting materials of OLEDs.The new two t-APE-type derivatives are applied to OLEDs devices showing that t-APE-type derivatives have the excellent properties for the emitting materials of OLEDs.Download high-res image (207KB)Download full-size image

•Anthraquinone dyes based on phenylamine/triphenylamines was synthesized.•The prepared dyes exhibited remarkable solvatochromic fluorescence.•The dyes showed large Stokes shifts (210–306 nm) in different organic solvents.•The nanometer cavity structure of prepared dye 3 was observed.Five donor-acceptor anthraquinone dyes based on phenylamine/triphenylamines with different substituted groups were synthesized by Suzuki reaction in good yields, and the photophysical properties were studied in organic solvents with different polarity. The title dyes exhibited remarkable solvatochromic fluorescence (>190 nm emission shift in polar media), which was derived from intramolecular charge transfer (ICT) character that revealed by DFT/TD-DFT calculation. And large Stokes shifts (210–306 nm) were observed in different organic solvents, along with rich color changes from blue to green, yellow, orange and even purple-red. The Stokes shifts were linearly dependent on the solvent polarity function ET(30). Interestingly, it was found from the single-crystal X-ray diffraction analysis that dye 3 displayed two different interleaved channel structures, which was seldom seen in organic compounds and could be used as host for complexation potentially. Electrochemical characterization suggested that the different substituted phenylamine groups attached to anthraquinone unit could lead to tunable potentials and energy levels.

With the dramatic development of the power conversion efficiency (PCE) of perovskite solar cells (PSCs), the device lifetime has attracted extensive research interest and concern. To enhance device durability, developing dopant-free hole-transporting materials (HTMs) with a high performance is a promising strategy. Herein, three new HTMs with a N,N′-diphenyl-N,N′-di(m-tolyl)benzidine (TPD) core: TPD-4MeTPA, TPD-4MeOTPA and TPD-4EtCz are designed and synthesized, showing suitable energy levels and excellent film-formation properties. PCEs of 15.28% were achieved based on pristine TPD-4MeOTPA as the HTM, which is a little lower than that of the p-doped 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD)-based device (17.26%). Importantly, the devices based on the new HTMs show relatively improved stability compared to devices based on spiro-OMeTAD when aged under ambient air with 30% relative humidity in the dark.

•Two novel and low-cost thiophene-based hole transporting materials were designed and synthesized.•The newly developed Z26 based perovskite solar cell exhibited a remarkable PCE of 20.1%.•The devices show relatively better stability than that of spiroOMeTAD under ambient air and illumination.•The cost of the new HTMs are much cheaper than that of spiroOMeTAD.The exploration of alternative low-cost molecular hole-transporting materials (HTMs) for both highly efficient and stable perovskite solar cells (PSCs) is a relatively new research area. Two novel HTMs using the thiophene core were designed and synthesized (Z25 and Z26). The perovskite solar cells based on Z26 exhibited a remarkable overall power conversion efficiency (PCE) of 20.1%, which is comparable to 20.6% obtained with spiroOMeTAD. Importantly, the devices based-on Z26 show better stability compared to devices based on Z25 and spiroOMeTAD when aged under ambient air of 30% or 85% relative humidity in the dark and under continuous full sun illumination at maximum power point tracking respectively. The presented results demonstrate a simple strategy by introducing double bonds to design hole-transporting materials for highly efficient and stable perovskite solar cells with low cost, which is important for commercial application.Two novel and low-cost thiophene-based hole transporting materials were designed and synthesized. The newly developed Z26 based perovskite solar cell exhibited a remarkable PCE of 20.1% along with enhanced stability under ambient air and illumination.Download high-res image (149KB)Download full-size image

•Two simple piperazine derivates HTMs with p-π conjugated structure were synthesized.•Two HTMs exhibit good thermal stabilities, suitable HOMO levels and wide band gaps.•The solution-processed PSC based on dopant-free Me-QTPA achieved a PCE of 9.07%.•The PSCs with dopant-free Me-QTPA remain almost constant after 600 h with a contact angle of 101.6° to water.Two simple hole-transporting materials, Me-QTPA and Me-BPZTPA, which consist of p-π conjugated structure, have been synthesized and studied in solid-state perovskite solar cells. Me-QTPA and Me-BPZTPA show outstanding thermal stabilities and appropriate HOMO levels; in addition, these two materials show wide band gaps, thus they can block the electron transport and hence suppress the carrier recombination. The solution-processed CH3NH3PbI3-based device using dopant-free Me-QTPA and Me-BPZTPA can achieve a power conversion efficiency of 9.07% and 8.16%, respectively. The perovskite solar cells with dopant-free Me-QTPA show better performance than the cells with dopant-free spiro-OMeTAD, especially in long-term stability. The power conversion efficiency for the perovskite solar cells with dopant-free Me-QTPA remains almost constant after 600 h. The dopant-free Me-QTPA layer shows strong hydrophobicity with a contact angle of 101.6° to water, which indicates that Me-QTPA has a promising long-term stability at room temperature.Molecular structure of the p-π conjugated Me-QTPA; J-V curves and configuration schematic diagram for the perovskite solar cell fabricated with dopant-free Me-QTPA.Download high-res image (106KB)Download full-size image

Based on Y-type titanylphthalocyanine nanoparticles (Y-TiOPc NPs) with an average diameter of 2.5 ± 0.6 nm, a trap-assisted ultrasensitive near-infrared organic photodetector (NIR OPD) has been successfully fabricated using the dip-coating process. The prepared OPD exhibited an obvious photomultiplication phenomenon with the highest external quantum efficiency (EQE) of 354200%, an excellent photosensitivity with the maximum photoresponsivity (R) of 2227 A W−1, and an outstanding low-light detection with the highest normalized detectivity (D*) of 3.1 × 1014 Jones under 780 nm illumination with a low intensity of 0.1 μW cm−2 at +15 V μm−1. Such performances were attributed to the ultrasmall Y-YiOPc NPs with remarkable photosensitivity and a high surface-to-volume ratio which can enhance external hole tunneling injection assisted by trapped-electrons at the photoactive layer/ITO interface. The high EQE and R properties of the device, as well as the prompt, steady and reproducible photocurrent response during repeated on/off cycles of illumination, suggested that the prepared OPD was desired for ultrasensitive NIR detection. Therefore, the ultrasmall Y-TiOPc NPs proposed in this study showed great promising application in the large-area and low-cost solution process of ultrasensitive NIR OPDs.

•Firstly present the microemulsion phase transfer method for preparing Y-TiOPc NCs.•Y-TiOPc NCs with ultrasmall and high crystal stability are prepared by this method.•Y-TiOPc NCs show high solvent-stabilized dispersibility and ultra-photosensitivity.•Y-TiOPc NCs could be used in other solution-processed photoelectric devices.A microemulsion phase transfer method was developed to prepare Y-type titanylphthalocyanine nanocrystals (Y-TiOPc NCs) with an average diameter of 2.3 ± 0.8 nm. The purification and crystal transformation of TiOPc could be achieved in the one-step process by establishing a stable H2O/o-dichlorbenzene microemulsion at high shear rate. The photoelectric characteristics of the ultrasmall Y-TiOPc NCs were evaluated by acting as the photoactive materials in organic photoreceptors, which afforded an impressive photosensitivity of E1/2 = 0.064 μJ/cm2. The dispersion of the Y-TiOPc NCs in a solution of polyvinyl butyral, methylethylketone and cyclohexanone (PVB/MEK/CYC) showed excellent dispersibility (zeta potential: –50.0 mV) at least 60 days and suffered no photoelectric penalty. The excellent solvent-stabilized dispersibility mainly relied on electrostatic repulsion force resulting from the high charge-mass ratio due to ultrasmall particle size.Y-TiOPc NCs featured by ultrasmall particle size of 2.3 ± 0.8 nm, high crystal stability, excellent solvent-stabilized dispersibility and ultra-photosensitivity were successfully prepared by the microemulsion phase transfer method.

We report two simple triphenylamine-based hole-transporting materials (HTMs) containing vinyl derivatives, 3,6-di(2-(4-(N,N-di(p-tolyl)amino)phenyl)vinyl)-2-thiophene (apv-T) and 3,6-di(2-(4-(N,N-di(p-tolyl)amino)phenyl)vinyl)-9-ethyl-carbazole (apv-EC) for the perovskite solar cells. According to theoretical calculation and experimental results, their HOMO energy levels are similar to that of conventional spiro-OMeTAD, which is supposed to be favorable for the hole transportation in the device. Up to 12% of light-to-electricity conversion efficiency has been achieved for the mesoporous TiO2/CH3NH3PbI3/apv-EC/Au solar cell without using p-type dopants. Time-resolved photoluminescence (PL) measurement and Electrochemical Impedance Spectra (EIS) further reveal that relatively high hole mobility of the apv-EC and weak recombination occurred at TiO2/CH3NH3PbI3/apv-EC interfaces of the device are crucial to the good performance in comparison with the apv-T. Advantages such as easy synthesis, low cost and relatively good cell performance provide a potential application as the replacement of the expensive spiro-OMeTAD.

CH3NH3PbI3 perovskite solar cells with 2TPA-n-DP (TPA = 4,4′-((1E, 1′E,3E,3′E)-[1,1′-biphenyl]-4,4′-diylbis(buta-1,3-diene-4,1-diyl)); DP = bis(N,N-di-p-tolylaniline); n = 1, 2, 3, 4) as hole-transporting materials (HTMs) have been fabricated. After optimization of the mesoporous TiO2 film thickness, devices based on 2TPA-2-DP with power conversion efficiencies (PCEs) of up to 12.96% have been achieved, comparable to those of devices with (2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene) (spiro-OMeTAD) as HTM under similar conditions. Further time-resolved photoluminescence (PL) measurements showed a fast charge transfer process at the perovskite/2TPA-2-DP interface. With the aid of electrochemical impedance spectra, a study of the electron blocking ability of 2TPA-2-DP in the device reveals that the presence of 2TPA-2-DP can greatly increase charge transfer resistance at the HTM/Au interface in the device, thus reducing the recombination. Furthermore, the perovskite solar cells based on these four HTMs exhibit good stability after testing for one month.

In this paper, we reported a novel non-aqueous electrorheological (ER) fluid structured by TiO2 nano-particle-modified poly (methyl methacrylate) (PMMA/TiO2) dispersed in low viscosity Isopar L and its electrorheological behaviors were researched. Titanium dioxide nano-particles modified with poly (methyl methacrylate) were prepared via in situ polymerization and characterized by Fourier transform infrared, thermogravimetry, and transmission electron microscopy. The thickness of the cladding layer of nano-titanium dioxide surface was about 2∼3 nm, and the cladding rate was 1.437 %. A non-aqueous electrorheological (ER) fluid was constituted by PMMA/TiO2 particles dispersed in Isopar L. The influence of the electric field intensity, the mass concentration of the PMMA/TiO2, and the temperature on the electrorheological properties of ER fluid were discussed, respectively. The research results showed that the ER fluid performed a well rheological property when an external electric field was applied, and with the increase of the electric field intensity, from 0 to 4.5 kV/mm, the shear stress was increased from about 3 to 30 Pa. Meanwhile, the electrorheological effect and shear stress were also strengthened with temperature elevated, and the mass concentration of PMMA/TiO2 particles increased in dispersed system, respectively.

Two new triphenylamine-based hole-transporting materials (HTMs) containing butadiene derivatives are employed in CH3NH3PbI3 perovskite solar cells. Up to 11.63% of power conversion efficiency (PCE) has been achieved. Advantages such as easy synthesis, low cost and relatively good cell performance exhibit a possibility for commercial applications in the future.

A thin wide band gap organic semiconductor N,N,N′,N′-tetraphenyl-benzidine layer has been introduced by spin-coating to engineer the metal–semiconductor interface in the hole-conductor-free perovskite solar cells. The average cell power conversion efficiency (PCE) has been enhanced from 5.26% to 6.26% after the modification and a highest PCE of 6.71% has been achieved. By the aid of electrochemical impedance spectroscopy and dark current analysis, it is revealed that this modification can increase interfacial resistance of CH3NH3PbI3/Au interface and retard electron recombination process in the metal–semiconductor interface.Keywords: metal−semiconductor (M−S) interface; modification; N,N,N′,N′-tetraphenyl-benzidine (TPB); perovskite solar cell;

•A novel ER fluid is prepared by PLMA/TiO2 dispersed in low-viscosity isoparaffin.•PLMA/TiO2 ER fluid shows perfect electrorheological behavior under electric field.•PLMA/TiO2 ER fluid is successfully used for electrophoretic displays.•The maximum contrast ratio of a micro-cup device is 6.2 and response time is 288 ms.In this paper, we reported a new non-aqueous electrorheological (ER) fluid structured by TiO2 nano-particle modified poly(lauryl methacrylate) (PLMA/TiO2) dispersed in low viscosity isoparaffin and studied its electrorheological behaviors. Moreover, the ER fluid was applied to electrophoretic display at the first time. PLMA/TiO2 particles were prepared via graft copolymerization using γ-methacryloxypropyltrimethoxysilane and lauryl methacrylate, successively. The thickness of the cladding layer of nano titanium dioxide surface was about 2.9 nm. When an external electric field was applied to this dispersed system, from 0 to 4.5 kV/mm, the ER fluid showed a good rheological property and the viscosity of ER fluid was increased from 20 to 160 mPa s. The shear stress strengthened with PLMA/TiO2 particles weight fraction increase in dispersed system. As a white medium, the ER fluid was mixed with carbon black to prepare a micro-cup electrophoretic display device, which could successfully realize electrophoretic display for white and black state under an electric field. The maximum contrast ratio of the micro-cup device was 6.2, and response time was 288 ms, and the clock micro-cup device could maintain display state than 24 h in the absence of electric fields.

Four novel blue luminescent hole transporting materials with N,N′-di(p-tolyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine as the core, containing triphenylamine units and olefinic linkers were synthesized and characterized by FT-IR, 1H NMR and HRMS. Their optical, electrochemical and thermal properties were investigated. Quantum-chemical calculations were performed to obtain their optimized structures and the electron distribution of the molecular orbital energy levels, and the experimental findings suggest that monosubstituted compounds have a similar energy gap to the bisubstituted compounds. The UV–Vis and photoluminescence spectra indicate that these compounds are blue luminescent materials. Cyclic voltammetry measurements show that the four compounds embody suitable highest occupied molecular orbital levels (in a range of −5.08 ∼ −5.14 eV) for hole injection. All of the compounds have excellent thermal stability, with decomposition temperatures above 400 °C and glass transition temperatures above 100 °C, which is of benefit to form stable amorphous glassy states.Graphical abstractHighlights► Four novel blue luminescent hole transporting materials containing triphenylamine units and olefinic linkers were synthesized and characterized. ► The synthesized compounds exhibit blue emissions, good solubility, the appropriate highest occupied molecular orbital energy level and high thermal stability. ► Quantum chemical calculations suggest that the energy gap can be effectively reduced by enlarge any part of conjugated structure. ► The new compounds offer potential for application in organic light-emitting devices.

Two new blue luminescent hole transporting materials (HTM) containing triphenylamine, carbazole units and olefinic linkers (TM1 and TM2) were synthesized via Wittig reaction and characterized by 1H NMR, FT-IR, and HRMS. The compounds show good solubility in common organic solvents such as dichloromethane, chloroform, tetrahydrofuran and dimethyl formamide. Their optical, electrochemical and crystalline properties were investigated by using UV–Vis, photoluminescence (PL) spectra, cyclic voltammetry (CV) and differential scanning calorimetry (DSC), respectively. Quantum-chemical calculation was performed to obtain their optimized structures and the electron distribution of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. The UV–Vis absorption and PL spectra of the two compounds in solid state were found to be similar to that when they were in dilute THF, which suggests that these compounds remain as an amorphous state in solid films. CV measurements show that the two compounds embody suitable HOMO levels (in a range of −5.28 to −5.23 eV) for hole injection, which is consistent with the calculation consequence. Two compounds possess high glass-transition temperature (Tg) at 96.61 and 90.74 °C for TM1 and TM2, respectively, suggesting the two compounds could form stable amorphous glassy states. The experimental results show that the synthesized compounds have great potential for application in organic light-emitting devices (OLEDs).Graphical abstractHighlights► Two novel hole transporting materials were synthesized and characterized. ► Synthesized compounds exhibited good optoelectronic and thermal properties. ► Quantum chemical calculations have been utilized to support the experimental. ► Synthesized compounds have great potential for application in OLEDs.

Titanylphthalocyanine (TiOPc) as hole transporting material (HTM) was successfully synthesized by a simple process with low cost. Perovskite solar cells using the TiOPc as HTM were fabricated and characterized. TiOPc as HTM plays an important role in increasing the power conversion efficiency (PCE) by minimizing recombination losses at the perovskite/Au interface because TiOPc as HTM can extract photogenerated holes from the perovskite and then transport quickly these charges to the back metal electrode. In the research, the β-TiOPc gives a higher PCE than α-TiOPc for the devices due to sufficient transfer dynamics. The β-TiOPc was applied in perovskite solar cells without dopping to afford an impressive PCE of 5.05% under AM 1.5G illumination at the thickness of 40 nm which is competitive with spiro-OMeTAD at the same condition. The present work suggests a guideline for optimizing the photovoltaic properties of perovskite solar cells using the TiOPc as the HTM.J–V curve of FTO/TiO2/CH3NH3PbI3/spiro-OMeTAD/Au solar cell (left) and the molecular structure of TiOPc (right).Download high-res image (113KB)Download full-size image

Two electron-rich, solution-processable phenonaphthazine derivatives, 5,12-bis{N-[4,4′-bis-(phenyl) -aminophen-4′′-yl]}-phenonaphthazine (BPZTPA) and 5,12-bis{N-[4,4′-bis(methoxy-phenyl)aminophen-4′′-yl]} -phenonaphthazine (MeO-BPZTPA) have been designed and employed in the fabrication of perovskite solar cells. BPZTPA and MeO-BPZTPA exhibit excellent thermal stabilities, hole mobilities (∼10−4 cm2/(V .s)) and suitable HOMO levels (−5.34 and −5.29 eV, respectively) relative to the valence band of the CH3NH3PbI3 and Au work function, showing their potential as alternative hole-transporting materials (HTMs). Meanwhile, the corresponding mesoporous TiO2/CH3NH3PbI3/HTM/Au devices are investigated, and the best power conversion efficiency of 10.36% has been achieved for MeO-BPZTPA without using p-type dopant.Download high-res image (172KB)Download full-size image

Based on Y-type titanylphthalocyanine nanoparticles (Y-TiOPc NPs) with an average diameter of 2.5 ± 0.6 nm, a trap-assisted ultrasensitive near-infrared organic photodetector (NIR OPD) has been successfully fabricated using the dip-coating process. The prepared OPD exhibited an obvious photomultiplication phenomenon with the highest external quantum efficiency (EQE) of 354200%, an excellent photosensitivity with the maximum photoresponsivity (R) of 2227 A W−1, and an outstanding low-light detection with the highest normalized detectivity (D*) of 3.1 × 1014 Jones under 780 nm illumination with a low intensity of 0.1 μW cm−2 at +15 V μm−1. Such performances were attributed to the ultrasmall Y-YiOPc NPs with remarkable photosensitivity and a high surface-to-volume ratio which can enhance external hole tunneling injection assisted by trapped-electrons at the photoactive layer/ITO interface. The high EQE and R properties of the device, as well as the prompt, steady and reproducible photocurrent response during repeated on/off cycles of illumination, suggested that the prepared OPD was desired for ultrasensitive NIR detection. Therefore, the ultrasmall Y-TiOPc NPs proposed in this study showed great promising application in the large-area and low-cost solution process of ultrasensitive NIR OPDs.

Two new triphenylamine-based hole-transporting materials (HTMs) containing butadiene derivatives are employed in CH3NH3PbI3 perovskite solar cells. Up to 11.63% of power conversion efficiency (PCE) has been achieved. Advantages such as easy synthesis, low cost and relatively good cell performance exhibit a possibility for commercial applications in the future.