•We fabricated various ternary devices by adding squaraine derivatives with different energy levels.•The large potential barrier between additional material and host material disrupts the charge carrier transport and leads to significant recombination.•The PCE of 10% SQ-3 ternary device is enhanced by 21% resulted from improved photon harvesting and changeless charge carrier characteristics.The ternary solar cell has been proved as an elegant strategy to realize efficient bulk heterojunction (BHJ) organic solar cells (OSCs) by harvesting a larger range of photons than binary devices. In order to design such an efficient system, the charge carrier transport and recombination in ternary OPVs must be considered. We fabricated various ternary devices by adding squaraine derivatives (SQ-1, SQ-2, SQ-3, SQ-4 and SQ-5) with complementary absorption spectrum in near infrared region as the additional donor material into Poly [[9-(1-octylnonyl)-9H-carbazole-2, 7-diyl]-2, 5-thiophenediyl-2, 1, 3-benzothiadiazole-4, 7-diyl-2, 5-thiophenediyl] (PCDTBT): [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) host binary blend film in this paper. Through the charge carrier mobility and transient photovoltage (TPV) measurements, it is found that the incorporation of 10% SQ-5 with shallower Highest Occupied Molecular Orbital (HOMO) level hinders holes in transferring from SQ to PCDTBT, which leads to unbalanced charge carrier transport, significant charge recombination, and decrease of performance. On the contrary, the performance of ternary devices incorporated with 10% SQ-3 with deeper HOMO energy level is improved by 21% compared with binary devices, which can be attributed to increased photon harvesting and changeless charge carrier characteristics.Download high-res image (224KB)Download full-size imageTernary solar cells incorporated with various SQ dyes with different energy levels achieve different performance.

•Using an inverted structure to facilitate the solution-processed PLEDs.•Using ZnO/PEIE bilayer for the efficient electron injection and transportation.•Systematically investigating the hole current and the electron current within the PLEDs.•Using an ultrathin PMMA layer to tune the hole current and achieve balanced charges injection to the emission layer.In this work, an ultra-thin insulating layer, poly(methylmethacrylate) (PMMA), is incorporated between the emissive layer (EML) and hole transporting layer (HTL) within the inverted polymer light-emitting diodes (PLEDs). Such a structure helps to reduce the hole injection and balance the electrons and holes in the EML. PLEDs with optimal PMMA thickness of around 5.6 nm is observed to obtain a maximum current efficiency of 14.33 cd A−1, which corresponds to 7.07% improvement compared to that of the device without PMMA layer (13.5 cd A−1). The device with best performance exhibits a superior low driving voltage of 2.5 V at 1 cd m−2 and shows a lower efficiency roll-off current efficiency which sustains 85% of the maximum value when the current density reaches 140 mA cm−2.

•The performance of SQ-BP:PC71BM solar cells improved by adding Bis-PC71BM.•The PCE of ternary system with 5%wt Bis-PC71BM increased from 4.46% to 5.31%.•The TPV data exhibits a beneficial effect on reducing the charge recombination loss.The development of small molecule organic solar cells (SMOSCs) has attracted considerable attention and achieved comparable power conversion efficiency (PCE) with polymer solar cells. Here, we demonstrate a bulk heterojunction (BHJ) small molecular solar cell with PCE of 5.31% by incorporating Bisadduct of phenyl-C71-butyric acid methyl ester (Bis-PC71BM) as an additional acceptor material into the host binary blend of 2-[4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl]-4-[(4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl)-2,5-dien-1-ylidene]-3-oxocyclobut-1-en-1-olate (SQ-BP): [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The short circuit current (JSC) and the fill factor (FF) of ternary SMOSCs are improved by decreasing the carrier recombination loss, increasing exciton dissociation and enhancing the carrier transport. The transient photovoltage (TPV) measurement indicates that the gradient HOMO energy alignment suppresses the charge recombination and leads to the increased charge carrier lifetime in ternary SMOSCs. As a result, the PCE of ternary devices with 5 wt% Bis-PC71BM is about 20% greater than that of SQ-BP: PC71BM based binary SMOSCs.Download high-res image (248KB)Download full-size image

•A series of NaScF4:Yb3+/Er3+ UCNPs have been synthesized by a simple hydrothermal process.•The out colour from green to red in NaScF4:Yb3+/Er3+ are obtained by adjusting the reactions time.•The mechanism of the colour tuning is due to the defects of different samples.A series of water-soluble NaScF4:Yb3+/Er3+ upconversion nanoparticles (UCNPs) have been synthesized by a facile hydrothermal route. The samples display a high degree of uniformity and crystallization. The upconversion (UC) emissions from green to red in NaScF4:Yb3+/Er3+ nanoparticles are successfully obtained by adjusting the reaction time from 12 h to 2 h. The UC emission peaks at 541 nm, and 652 nm of all the samples excited by 980 nm correspond to the transitions of 4S3/2/2H11/2 → 4I15/2 and 4F9/2 → 4I15/2 of Er3+ions, respectively. The green UC emission at 541 nm decreases while the red emission at 652 nm increases gradually when the reaction time changes from 12 h to 2 h. This work provides a novel and facile way of tuning colour from green to red in NaScF4:Yb3+/Er3+ UCNPs. These water-soluble nanoball structures NaScF4:Yb3+/Er3+ UCNPs promise to be novel biological probes and possess other applications in many fields.

Upconversion phosphors (UCPs) that are free from interference from biological sample autofluorescence have attracted attention for in vivo and in vitro bioapplications. However, UCPs need to be water-dispersible, nanosized, and highly luminous to realize broad applications. Therefore, the aim of this research is to develop UCPs that meet these comprehensive criteria for in vitro diagnosis. To combine nano size with high luminous intensity, β-NaYF4:Yb3+,Er3+ upconversion nanocrystals (UCNPs) codoped with Li+ and K+ are prepared that display high upconversion intensities as well as small size. The strongest green and red emissions of the Na0.9Li0.07K0.03YF4:Yb3+,Er3+ nanocrystals are increased by 7 and 10 times, respectively, compared with those of the undoped NaYF4:Yb3+,Er3+ nanocrystals. A mild sol–gel surface modification method is used to produce water-phase dispersions and allow covalent biomolecule conjugation. The bioactivated UCNPs are used as a bioreporter and integrated with a classical lateral flow assay to establish an assay to accomplish simultaneous dual-target detection of Yersinia pestis and Burkholderia pseudomallei. The assay achieves a sensitivity of 103 CFU/test without cross-interference between two targets. The research provides a way to produce UCNPs with comprehensive properties for use as excellent optical reporters in in vivo and in vitro bioapplications.Keywords: covalent biomolecule conjugation; dual-target detection; Li+ and K+ codoping; NaYF4:Yb,Er nanocrystals; upconversion fluorescence;

We developed a colloidal synthesis of CsPbBr3 perovskite nanocrystals (NCs) at a relative low temperature (90 °C) for the bright blue emission which differs from the original green emission (∼510 nm) of CsPbBr3 nanocubes as reported previously. Shapes of the obtained CsPbBr3 NCs can be systematically engineered into single and lamellar-structured 0D quantum dots, as well as face-to-face stacking 2D nanoplatelets and flat-lying 2D nanosheets via tuning the amounts of oleic acid (OA) and oleylamine (OM). They exhibit sharp excitonic PL emissions at 453, 472, 449, and 452 nm, respectively. The large blue shift relative to the emission of CsPbBr3 bulk crystal can be ascribed to the strong quantum confinement effects of these various nanoshapes. PL decay lifetimes are measured, ranging from several to tens of nanoseconds, which infers the higher ratio of exciton radiative recombination to the nonradiative trappers in the obtained CsPbBr3 NCs. These shape-controlled CsPbBr3 perovskite NCs with the bright blue emission will be widely used in optoelectronic applications, especially in blue LEDs which still lag behind compared to the better developed red and green LEDs.Keywords: blue emission; CsPbBr3 perovskite; lamellar structures; nanoplatelets; nanosheets; quantum dots; shape control

In this paper, we present a smart two-step treated method to simultaneously improve the work function, conductivity, and transmittance of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). With the two-step treated PEDOT:PSS, the short-circuit current density of polymer solar cells (PSCs) based on PTB7-Th:PC71BM increases from 13.41 to 22.10 mA/cm2, and the power conversion efficiency increases from 7.35% to 9.82% with 33% improvement. The underlying mechanisms on performance improvement of PSCs can be summarized as follows: (1) two-step treated PEDOT:PSS with the improved work function and the conductivity, which contributes significantly to the charge collection of PSCs; and (2) two-step treated PEDOT:PSS with higher transmittance, which is of benefit to the light absorption of the active layer in PSCs.Keywords: conductivity; PEDOT:PSS; transmittance; two-step treated method; work function

The impact of two kinds of additives, such as 1,8-octanedithiol (ODT), 1,8-diiodooctane (DIO), diphenylether (DPE), and 1-chloronaphthalene (CN), on the performance of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) based polymer solar cell are investigated. The polymer solar cells (PSCs) of PffBT4T-2OD:PC71BM by using CN show a more improved PCE of 10.23%. The solubility difference of PffBT4T-2OD in DIO and CN creates the fine transformation in phase separation and favorable nanoscale morphology. Grazing incidence X-ray diffraction (GIXRD) data clearly shows molecular stacking and orientation of the active layer. Interestingly, DIO and CN have different functions on the effect of the molecular orientation. These interesting studies provide important guidance to optimize and control complicated molecular orientations and nanoscale morphology of PffBT4T-2OD based thick films for the application in PSCs.

•The color tuning and mechanism of upconversion emission from green to red in NaLuF4:Yb3+/Ho3+ nanocrystals by codoping with Ce3+.•Sliced TRES spectra of 500–700 nm UC emissions, the peak intensity is changed with the time increased.•Two efficient cross relaxation processes between Ho3+ and Ce3+ are found to be dominant UC pathways for tuning the emission color from green to red in single NaLuF4:Yb3+/Ho3+ nanocrystals.The upconversion (UC) luminescence nanocrystals of hexagonal phase NaLuF4:Yb3+/Ho3+ were prepared by a solvothermal process at 300 °C. The visible upconversion emission from green to red in Yb3+ and Ho3+ codoped β-NaLuF4 nanoparticles is successfully achieved by tridoping with Ce3+ ions (0–12 mol%) and the red emission intensity is enhanced gradually with the increasing Ce3+ concentration. In this work, results of XRD, SEM, EDS and TRES upconversion data demonstrate that Ce3+ ions are successfully incorporated into NaLuF4:Yb3+/Ho3+ nanoparticles. UC emissions at 541 nm and 644 nm of all prepared nanoparticles under 980 nm excitation correspond to the transitions of 5S2/5F4 → 5I8 and 5F5 → 5I8 of Ho3+ ions respectively. The decay curves of 541 nm emission under 980 nm pulse excitation are detected. The 541 nm emission decays fast when Ce3+ concentration increases. All results show that tuning from green to red upconversion can be realized in NaLuF4:Yb3+/Ho3+ nanocrystals via tridoping with different concentration of Ce3+ ions.

•Preparation of device capable of stored charges with insulator PMMA in OLEDs.•Mechanism analysis with transient EL measurement.•Realize the stored charges induced AC-EL which is distinct from other similar ELs.•Demonstrate AC-EL induced by stored charges with series of pulses in transient way.AC-driven organic light-emitting diodes (OLEDs) can overcome some reliability-related drawbacks to traditional DC-OLEDs. They imply the use of insulating layers in the device. In this work OLEDs containing an insulating layer of poly (methyl methacrylate) (PMMA) in storing charges with the thickness of 2, 6, 8, 10 nm have been prepared and investigated. The emission mechanisms of the device are analyzed considering transient and AC electroluminescence (EL) measurements. We show that charges are stored in the PMMA layer as surface charges and bulk charges. The former contribute to the occurrence of EL spike after the driving pulse with a decay tail for about 80 μs to 10nm PMMA device, and the latter can be released to emit light under reversed voltage more than 2 V because they are immobile unless under the stronger reversed field. Stored charges commonly are harmful for the performance of OLEDs devices due to quenching, nonradiative transition and the thermal energy accumulation even degradation. Whereas when operating under alternating current (AC) stress, we not only obtain the EL peak from injection charges under forward voltage, but also obtain another peak below the built-in voltage 4.3 V, whose peak point lies in −0.2 V. It turns to originate from stored charges so they become beneficial instead of weakening EL for reusing to produce light. All the results pave the way to realize AC driven OLEDs devices using these stored charges, to uncover the AC EL mechanisms and to improve their EL performance.

•The effect of DIO on charge generation and charge transport were studied carefully.•Positive effects of DIO for charge generation were proved by the results of IQE and Jph.•Negative effects of DIO for charge transport were investigated according to the TOF-SIMS.To obtain higher device performance, the ideal bulk heterojunction (BHJ) morphology should feature both nanophase separation to increase charge generation and bi-continuous percolating networks to increase charge transport. In this paper, solvent additive, 1,8-diiodooctane (DIO), was used in PTB7-Th:PC71BM blend to improve BHJ morphology. The effect of DIO on charge generation and charge transport were studied carefully. Experimental study indicated that the effect of DIO on charge generation and charge transport are conflicted. Positive effects of DIO, which were induced by nanophase separation for charge generation in BHJ, are proved by the results of internal quantum efficiency (IQE) and photocurrent density (Jph), and negative effects of DIO on charge transport has been investigated according to the time-of-flight secondary ion mass spectrometer (TOF-SIMS).The addition of DIO resulted in smaller domains and a more finely interpenetrating BHJ morphology which were good to charge generation. The addition of DIO also caused donor material (PTB7-Th) migrates or diffuses toward the low work function cathode which was unfavorable for charge transport.

•The non-doped PhOLED with the emitting layer of [CBP/Ir(ppy)3]n/CBP are prepared.•The delay EL measurements are used to elucidate the light emission mechanism in non-doped PhOLEDs.•The carrier transport and recombination processes depends on the number of non-doped EML.In this paper, the non-doped PhOLED based on 4,4′-bis(9-carbazolyl)-1,1′-biphenyl(CBP) and fac-tris(2-phenylpyridine) iridium(Ir(ppy)3) with the emitting layer of [CBP/Ir(ppy)3]n/CBP in which n is equal to 2,3,4 and 5, respectively, are prepared. The electroluminescence and the luminance-voltage-current density characteristics of devices are detected. The wavelength range of these devices is varied from 517 nm to 540 nm. And the delay EL measurements are used to elucidate the carrier recombination and light emission mechanism in non-doped PhOLEDs. In this technique, the devices are driven using a square pulse driving scheme, with a forward bias pulse width of 1 ms, which is sufficiently long for prompt EL to reach its steady-state intensity. The delay EL results show that changing the number of the non-doped EML leads to marked changes in the charge-trapping and host–host TTA patterns, which suggests that the carrier transport and recombination processes depends on the number of non-doped EML. When the number of non-doped EML is less than 3, only the trapped carrier recombination signal are detected in the delay EL measurement. For the devices with more non-doped EML than 3, both the trapped carrier recombination and host–host TTA signal are detected. All these results are discussed and give the evidence for the electroluminescence mechanism of prepared devices.The delay EL results show that changing the number of the non-doped EML, the carrier transport and recombination processes is affected.

•Tetragonal rare-earth ions codoped LiScF4 upconversion nanocrystals have been synthesized.•The phase, morphology and UC emission of LiScF4:20%Yb3+, 2%Er3+ nanocrystals can be influenced by reaction temperature and time.•LiScF4:20%Yb3+, 2%Er3+ nanocrystals emit yellow color emission under 980 nm excitation.•The UC mechanism in the codoped LiScF4 samples is studied.Tetragonal rare-earth ions codoped LiScF4 nanocrystals have been synthesized by a modified solvothermal method. The results revealed that the phase and morphology can be tailored through varying the synthesis conditions, such as reaction temperature and time. Meanwhile, the UC fluorescence emission spectra were measured. It turned out that the UC emission intensity can be significantly influenced by reaction temperature and time. Different from the NaYF4:20%Yb3+,2%Er3+ nanocrystals that usually emit green emission, yellow color emission can be observed in the LiScF4:20%Yb3+,2%Er3+ samples under 980 nm excitation, which illustrates that the obtained new phase LiScF4 is suitable as a promising host for efficient UC fluorescence generation and tunable UC emission spectra. Moreover, the UC mechanism was investigated in detail.

To enhance the light harvesting of polymer solar cells (PSCs), amphipathic Al core and PPh3 protective shell (Al@PPh3) nanoparticles (NPs) synthesized by a simple and facile wet chemical process are incorporated into the anode buffer layer of the PTB7:PC71BM blend PSCs. The optimized power conversion efficiency (PCE) of 6.29% is achieved, which is enhanced about 20% compared with the pristine device. It is attributed to the localised surface plasmon resonance (LSPR) effects of Al@PPh3 NPs incorporated in the buffer layer and the light absorption of devices is enhanced.

Multiple interfaces are necessary for exciton separation in bulk heterojunction (BHJ) solar cells and continuous pathways for carrier transportation in donor:acceptor blend films, especially along the vertical direction, for efficient charge collection. Therefore film morphology is critically important to satisfy both in the construction of high performance organic solar cells (OSCs). In this work, the cooperative effect of solvent additives and solvent flux treatment on film morphology was confirmed. Furthermore, the correlation between a single processing parameter and the resulting morphology has been investigated. Our results show that film morphology can be tuned by changing the volume fraction of the solvent additive. Beyond that, after methanol fluxing, the OSC performance improves significantly, as short circuit current density (JSC) increases from 13.85 mA cm−2 to 15.17 mA cm−2 and fill factor (FF) from 62.9% to 65.7%, simultaneously. As a result, power conversion efficiency (PCE) increases from 6.79% to 7.67%. The favorable morphology was further investigated using time-of-flight secondary-ion mass spectroscopy (TOF-SIMS), and atomic force microscopy (AFM).

An asymmetrical squaraine dye (Py-3) with its two electron-donating aryl groups directly linked to the electron-withdrawing squaric acid core possesses an ideal bandgap of 1.33 eV, together with an intense and broad absorption band in the range 550–950 nm. Hence, the resulting solution-processed solar cells display an impressive Jsc of 12.03 mA cm−2 and a PCE of 4.35%.

We demonstrate bulk heterojunction (BHJ) organic photovoltaics (OPVs) with a power conversion efficiency (PCE) of 6.39% by incorporating a small molecular compound 2-[4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl]-4-[(4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl)-2,5-dien-1-ylidene]-3-oxocyclobut-1-en-1-olate (SQ-BP) as the additional donor material into a poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) host binary blend. Incorporating SQ-BP into the PCDTBT:PC71BM host blend film increases the photon harvesting of a ternary photovoltaic device with a broad absorption spectrum from 300 nm to 750 nm, which results in an increased short-circuit current density (Jsc). In addition to efficient photon harvesting, Förster resonance energy transfer (FRET) between PCDTBT and SQ-BP is also the reason for the increase in Jsc. As a result, the PCE of ternary devices with 10 wt% SQ-BP is about 30% greater than that of PCDTBT:PC71BM-based binary OPVs.

•Preparation of device capable of stored charges with insulator PMMA in OLEDs.•Mechanism analysis with transient EL measurement.•Realize the optical application of stored charges by transient method, and few related papers have been reported.Organic light-emitting diodes (OLEDs) device capable of stored charges with poly (methyl methacrylate) (PMMA) layer is studied by transient electroluminescence measurements. The mechanism and optical application of stored carriers are elucidated. A spike after a driven pulse is found in the device with PMMA layer, which is attributed to the drifting back of accumulated electrons and trapped ones in shallow states, and the detrapping of latter may result in a long decay tail. A reversed post-pulse is applied to release the electrons in deep traps as they are immobile unless under a strong reversed field. Since the stored charges can lead to a great loss of carriers and weaken the performance of device, we find a way to use them in the form of light emitting with an enhanced intensity more than 3 times as against steady-state. So we have a good reason to believe if in a proper way, we can make full use of the stored charges in optical application.

Two solution-processed asymmetrical squaraines (ASQs) with cyclopenta[b]indolinyl (1a) and cyclopenta[b]indolyl (1b) as end cappers have been designed and synthesized. Although the internal molecular structure variations are minimal, the presence of the cyclopenta[b]indolinyl group endows 1a more planar molecular structure, which results in a much more compact solid-state structure (density is 1.317 g cm−3 for 1a but is 1.187 g cm−3 for 1b), dramatically affecting charge transport in the thin films. The hole mobility of 1a:PC71BM blended film is about 7 times higher than that of 1b:PC71BM. Consequently, the maximum power conversion efficiency (PCE) value of the organic photovoltaic cells (OPVs) based on 1a of up to 4.1%, approximately 80% higher than that of 1b, is one of the highest PCEs achieved for ASQ-based bulk-heterojunction (BHJ) OPVs.

A novel asymmetrical squaraine ASQ-5 bearing indoline as an end capper exhibits a low bandgap of 1.43 eV and a broad absorption band in the Vis-NIR region of 550–850 nm in thin films, hence renders solution-processed organic solar cells with an impressive Jsc of up to 11.03 mA cm−2 and an excellent PCE of 4.29%.

An asymmetrically substituted squaraine ASQC bearing a 9-carbazyl substituent exhibits an extremely deep HOMO energy level of −5.46 eV and a relatively low bandgap of 1.65 eV, hence renders solution-processed organic solar cells with an impressive Voc of up to 1.12 V and a PCE of 2.82%.

Two novel types of covalently ether-linked porphyrin–phthalocyanine (Por–Pc), heterodimer and heteropentamer, connected through the meso phenyl group of the porphyrin have been synthesized for the first time. The Por–Pc heterodimer and heteropentamer have more delocalized π-electrons and therefore their conjugated degree is higher. In addition, these compounds possess better solubility and a wider light absorption than typical single porphyrins and phthalocyanines. Solar cell devices based on as-synthesized porphyrin–phthalocyanine heterodimers and heteropentamers as donor materials and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor material are prepared and show a noticeably better performance. The suitable ZnPor–(O–ZnPc)4:PCBM weight ratio for photovoltaic devices is 4:1 and the highest photovoltaic properties are achieved based on ZnPor–(O–ZnPc)4:PCBM (4:1) annealed at 140 °C in a vacuum for 20 min. The highest PCE is 2.08.

A near-ultraviolet light emitting diode (LED) consisting of ZnO nanorods/MEH-PPV heterostructure and a layer of ZnS as the modification buffer layer is reported. Specially, the ZnO nanorods are grown on the ZnS hole-injecting buffer layer by hydrothermal method. Then the devices of ITO/ZnS/ZnO/ZnOnanorods/MEH-PPV/Al are prepared. Under forward bias, not only strong near-ultraviolet (N-UV) electroluminescence (EL) at 380 nm of ZnO band edge emission and weak defect-related emissions of ZnO nanorods at 410, 510 and 760 nm are observed, but also the exciton emission of MEH-PPV at 580 nm is detected. Along with increasing the thickness of ZnS film, the emission at 580 nm strengthens. Compared with the device ITO/ZnO/ZnOnanorods/MEH-PPV/Al we have reported in the past, the experimental results show that the suitable insertion of a ZnS thin layer can enhance the N-UV EL. Under the same voltage, the light intensity can be increased up to 10 times more than that of the device without a ZnS layer. Moreover, the turn-on voltage is reduced remarkably. The effect of ZnS as the hole-injecting buffer layer with different thickness on the EL of ZnO nanorods/MEH-PPV heterostructure is investigated.Graphical abstractA near-ultraviolet light emitting diode (LED) consisting of ZnO nanorods/MEH-PPV heterostructure and a layer of ZnS as the modification buffer layer is reported. Under forward bias, the near-ultraviolet (N-UV) electroluminescence (EL) at 380 nm of ZnO band edge emission is observed. When the thickness of ZnS layer is suitable, the light intensity of the device with ZnS can be increased up to 10 times more than that of the device without a ZnS layer.Research highlights► A layer of ZnS as the modification buffer layer is used to imporve the near-ultraviolet electroluminescence of ZnO nanorods/MEH-PPV heterostructure diode. ► Under forward bias, the near-ultraviolet electroluminescence at 380nm of ZnO band edge emission is observed. ► When the thickness of ZnS layer is suitable, the light intensity of the device with ZnS can be increased up to 10 times more than that of the device without a ZnS layer.

Three electron-deficient conjugated polymers based on perylene diimide (PDI) units, namely, poly[(N,N′-didodecyl-3,4,9,10-perylene diimide-1,7-diyl)-alt-(9,9-dihexylfluorene-2,7-diyl)] (PPDIF), poly{(N,N′-didodecyl-3,4,9,10-perylene diimide-1,7-diyl)-alt-[N-(2-ethylhexyl) carbazole-3, 6-diyl]} (PPDIC) and poly{(N,N′-didodecyl-3,4,9,10-perylene diimide-1,7-diyl)-co-[N-(2-ethylhexyl) carbazole-3,6-diyl]-co-(9,9-dihexylfluorene-2,7-diyl)} (PPDICF) have been synthesized via Suzuki coupling reaction, and their chemical structures are confirmed by 1H NMR, 13C NMR and FT-IR. All these polymers show broad absorption bands in 250–700 nm, and their optical band gaps are calculated to be ~1.7 eV. Cyclic voltammetry results confirm that the objective macromolecules possess high electron affinity of ~3.9 eV. By employing poly-3-hexylthiophene (P3HT) as electron donor and PPDIC as electron acceptor, all polymer solar cells (aPSCs) with bulky heterojunction structure have been fabricated, preliminary results indicate they have one of the most highest open-circuit voltage (Voc) (0.86 V) reported so far in aPSCs with PDI-based polymers as electron acceptor.

ZnO nanorods are synthesised by a hydrothermal method on ITO glass. Then ITO/ZnO/ZnO nanorod/MEH-PPV/Al heterostructure devices are fabricated. Under DC bias, ultraviolet (UV) electroluminescence (EL) at 380 nm from ZnO band edge emission is observed. In addition, exciton emission of MEH-PPV at 580 nm and defect related emission of ZnO nanorods at 640 nm and 747 nm are also detected. Upon increasing the applied voltage, the UV EL becomes predominant and is much stronger than other emissions at 28 V. The mechanisms of ZnO band edge emission and background emission are discussed.

•One dimensional TiO2@MWCNTs core-shell photocatalyst constructed.•The TiO2 nanoparticles are highly dispersed on the MWCNTs.•The layer thickness adjusted for different nanocomposites.•The 1D heterojunction enhancing electron transfers.With the distinct electronic and optical properties, multiwall carbon nanotubes (MWCNTs) are identified as an outstanding catalyst support, which can effectively improve the performance of the TiO2 photocatalysts. Herein, the unique one dimensional TiO2@MWCNTs nanocomposites have been prepared by a facile hydrothermal method. The TiO2 coating layers are extremely uniform and the thickness is adjustable for different nanocomposites. XPS measurements confirm that intimate electronic interactions are existed between MWCNTs and TiO2 via interfacial TiOC bond and the photoluminescence intensity of the TiO2@MWCNTs nanocomposites are effectively quenched compared with pure TiO2, suggesting the fast electron transfer rates. The thickness of TiO2 coating layers of the TiO2@MWCNTs nanocomposites plays a significant role in the photocatalytic degradation of organic pollutants, such as methylene blue (MB) and Rhodamine B (RhB), and photocatalytic H2 evolution from water. Due to the formation of one dimensional heterojunction of TiO2@MWCNTs nanocomposites and the positive synergistic effect between TiO2 and carbon nanotubes, it is found that the photocatalytic activity of the system is significantly improved.

To enhance the light harvesting of polymer solar cells (PSCs), amphipathic Al core and PPh3 protective shell (Al@PPh3) nanoparticles (NPs) synthesized by a simple and facile wet chemical process are incorporated into the anode buffer layer of the PTB7:PC71BM blend PSCs. The optimized power conversion efficiency (PCE) of 6.29% is achieved, which is enhanced about 20% compared with the pristine device. It is attributed to the localised surface plasmon resonance (LSPR) effects of Al@PPh3 NPs incorporated in the buffer layer and the light absorption of devices is enhanced.

An asymmetrical squaraine dye (Py-3) with its two electron-donating aryl groups directly linked to the electron-withdrawing squaric acid core possesses an ideal bandgap of 1.33 eV, together with an intense and broad absorption band in the range 550–950 nm. Hence, the resulting solution-processed solar cells display an impressive Jsc of 12.03 mA cm−2 and a PCE of 4.35%.

Two solution-processed asymmetrical squaraines (ASQs) with cyclopenta[b]indolinyl (1a) and cyclopenta[b]indolyl (1b) as end cappers have been designed and synthesized. Although the internal molecular structure variations are minimal, the presence of the cyclopenta[b]indolinyl group endows 1a more planar molecular structure, which results in a much more compact solid-state structure (density is 1.317 g cm−3 for 1a but is 1.187 g cm−3 for 1b), dramatically affecting charge transport in the thin films. The hole mobility of 1a:PC71BM blended film is about 7 times higher than that of 1b:PC71BM. Consequently, the maximum power conversion efficiency (PCE) value of the organic photovoltaic cells (OPVs) based on 1a of up to 4.1%, approximately 80% higher than that of 1b, is one of the highest PCEs achieved for ASQ-based bulk-heterojunction (BHJ) OPVs.

An asymmetrically substituted squaraine ASQC bearing a 9-carbazyl substituent exhibits an extremely deep HOMO energy level of −5.46 eV and a relatively low bandgap of 1.65 eV, hence renders solution-processed organic solar cells with an impressive Voc of up to 1.12 V and a PCE of 2.82%.

A novel asymmetrical squaraine ASQ-5 bearing indoline as an end capper exhibits a low bandgap of 1.43 eV and a broad absorption band in the Vis-NIR region of 550–850 nm in thin films, hence renders solution-processed organic solar cells with an impressive Jsc of up to 11.03 mA cm−2 and an excellent PCE of 4.29%.

We demonstrate bulk heterojunction (BHJ) organic photovoltaics (OPVs) with a power conversion efficiency (PCE) of 6.39% by incorporating a small molecular compound 2-[4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl]-4-[(4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl)-2,5-dien-1-ylidene]-3-oxocyclobut-1-en-1-olate (SQ-BP) as the additional donor material into a poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) host binary blend. Incorporating SQ-BP into the PCDTBT:PC71BM host blend film increases the photon harvesting of a ternary photovoltaic device with a broad absorption spectrum from 300 nm to 750 nm, which results in an increased short-circuit current density (Jsc). In addition to efficient photon harvesting, Förster resonance energy transfer (FRET) between PCDTBT and SQ-BP is also the reason for the increase in Jsc. As a result, the PCE of ternary devices with 10 wt% SQ-BP is about 30% greater than that of PCDTBT:PC71BM-based binary OPVs.