Electron Injection Barrier Research Articles

Exploring the Effect of Electron Withdrawing Groups on Optoelectronic Properties of Pyrazole Derivatives as Efficient Donor and Acceptor Materials for Photovoltaic Devices

Abstract Multifunctional pyrazole derivative, i.e. 3-amino-1-(5-hydroxy-3-methyl-1H-pyrazol-4-yl)-1H-benzo[f]chromene-2-carbonitrile (PBCC) has been synthesized and characterized. To shed light on various properties of interests, the ground state geometry was optimized by adopting Density Functional Theory (PBE/TZ2P). The effect of different functionals on the absorption wavelengths was studied by using Time-Domain DFT (TDDFT), e.g. GGA functional PBE, hybrid functionals B3LYP and PBE0, rang separated functionals CAM-B3LYP, LCY-PBE and CAMY-B3LYP, Dispersion Corrections PBE-D3 and B3LYP-D3. Among all these functionals PBE and PBE-D3 were found to be good choices which reproduced the absorption spectra of the PBCC. With the aim to enhance the electro-optical, charge transfer and photovoltaic properties, five new derivatives were designed by di-substituting the –F, –Cl, –Br, –COOH and –CN at benzochromene moiety. The electron injection barrier, band gap alignment and related calculated photovoltaic parameters revealed that PBCC and its newly designed derivatives would be proficient to be used in photovoltaic devices. These compounds can be used as donor materials in dye-sensitized solar cells (DSSCs) with favorable type-II band alignment. Moreover, PBCC and most of its derivatives might also be good choice as efficient acceptors with poly(dithieno[3,2-b:2,3-d]pyrrole thiophene) (PDTPr-T) and donor materials with Phenyl-C61-butyric acid methyl ester (PC61BM) in organic solar cells.

Low temperature processed efficient and stable perovskite solar cell

MA0.6FA0.4PbI3 material based efficient and stable perovskite solar cells (PSCs) are fabricated by electron transport layer (ETL) interfacial modification. The highest power conversion efficiency (PCE) of device was ~ 17%. Cesium acetate and cesium carbonate were used with low temperature processed sol-gel ZnO ETL for interface modifications. Low leakage current and enhanced dark injection current are observed from dark current-voltage measurement. From the electrochemical impedance spectroscopy (EIS) measurement higher recombination resistance and lower interfacial contact resistance are observed in the PSC devices. Mott-Schottky analysis also shows the higher flat-band potential and enhanced device performance with cesium acetate ETL. Cesium acetate related ZnO ETL has large grain size which leads to reduce the device series resistance and contact resistance in PSC compared to cesium carbonate ETL related device. Perovskite film on cesium acetate ETL has better surface morphology, topography and hydrophobicity characterization compared to perovskite film grown on cesium carbonate ETL film. The material work function and electron injection barrier are also investigated by X-Ray photoelectron spectroscopy (XPS) measurement and ultraviolet photoelectron spectroscopy (UPS). From electrochemical impedance spectroscopy measurements the charge transport behaviour and trap-assisted carrier recombination are estimated. Fabricated PSCs device stability has been measured for a month-long degradation study. The PSC device stability is observed four times higher with cesium acetate PSCs compared to cesium carbonate ETL related PSCs. The overall device PCE is around 82% higher with cesium acetate compared to cesium carbonate devices.

Tunable Schottky barriers in ultrathin black phosphorus field effect transistors via polymer capping

It is still a great challenge to avoid the degradation of ultrathin black phosphorus (BP) since its discovery in 2014. Various methods have been explored to stabilize the properties of ultrathin BP through capping technology or chemical passivation. Besides, the large metal–semiconductor contact resistance is also one of the critical issues. The two problems hinder the further development of ultrathin BP devices. Herein, we demonstrate that polymethyl methacrylate (PMMA) capping can not only enhance the durability of the ultrathin BP effectively and nondestructively, but also tune the effective Schottky barriers (SBs) formed at the interfaces between the metal and semiconductor dramatically. Particularly, the Schottky barrier (SB) for electron injection from metal to semiconductor is decreased by ~13 meV and the performance of the BP field effect transistor (FET) is strongly enhanced with the current on/off ratio increased by 6.8 times for the hole conduction after the PMMA capping. In addition, after the electron beam irradiation to the PMMA layer, the charge neutral point of the BP FET exhibits remarkable negative shift resulting in the electron dominated semiconductor channel at zero gate voltage. Furthermore, through partially capping the BP channel, a prototype of BP p-n diode was demonstrated with a maximum rectification factor of 21.3. The diode performs quite well with just a quarter of the BP channel capped by the PMMA layer. Our findings suggest that the PMMA capped ultrathin BP would be a promising choice for future device applications.

New types of organic semiconductors based on diketopyrrolopyrroles and 2,1,3-benzochalcogenadiazoles: a computational study.

A comprehensive computational study is performed on model compounds based on 2,1,3-benzochalcogenadiazoles and diketopyrrolopyrroles of A-π-A'-π-A architecture (A and A' represent 2,1,3-benzochalcogenadiazoles and diketopyrrolopyrroles, respectively, and π is the bridging unit between them including thiophene, furan, and selenophene) for their utility as organic semiconductors. The compounds were found to possess planar geometry, which is a desired property for organic semiconductors. The electronic properties, including adiabatic and vertical electron affinity (EA), adiabatic and vertical ionization potential (IP), reorganization energy (λ), hole injection barrier and electron injection barrier, transfer integral, and charge mobility, were calculated. The electron affinity is higher in the case of thiophene/selenophene as the linker for a given terminal benzochalcogenadiazole than the corresponding compounds with furan as a linker, while the ionization potential is lowest for compounds having selenophene as the linker with a given terminal benzochalcogenadiazole moiety than the compounds having furan or thiophene as a linker. The hole injection barrier in these compounds is lower than the electron injection barrier, which facilitates the hole injection from the metal electrode, while hole reorganization energy is found to be larger than the electron reorganization energy. The compounds possess hole mobilities in the range of 2.50-4.91cm2/Vs and electron mobilities in a similar range of 4.58-9.68cm2/Vs. This study reveals that compounds based on a combination of diketopyrrolopyrrole and 2,1,3-benzochalcogenadiazole units would exhibit hole transporting properties and act as potential ambipolar materials.

Flexibility of Semitransparent Perovskite Light-Emitting Diodes Investigated by Tensile Properties of the Perovskite Layer.

Organic-inorganic hybrid perovskites have been investigated extensively for use in perovskite-based solar cells and light-emitting diodes (LEDs) because of their excellent electrical and optical properties. Although the flexibility of perovskite LEDs has been studied through empirical methods such as cyclic bending tests, the flexibility of the perovskite layer has not been investigated systemically. Here, flexible and semitransparent perovskite LEDs are fabricated: a PEDOT:PSS anode and Ag nanowire cathode allow for flexible and semitransparent devices, while the use of a conjugated polyelectrolyte as an interfacial layer reduces the electron injection barrier between the cathode and the electron transport layer (SPW-111), resulting in enhanced device efficiency. Cyclic bending tests performed on the electrodes and in situ hole-nanoindentation tests performed on the constituent materials suggest that mechanical failure occurs in the perovskite MAPbBr3 layer during cyclic bending, leading to a decrease in the luminance. Tensile properties of the MAPbBr3 layer explain the critical bending radius ( rb) of the perovskite LEDs on the order of 1 mm.

Perovskite light-emitting diodes based on n-type nanocrystalline silicon oxide electron injection layer

Organometal halide perovskites featuring solution-processable characteristics, high photoluminescence quantum yield (PLQY), and color purity, are an emerging class of semiconductor with considerable potential applications in optoelectronic devices. Electron injection layer is an important component of perovskite light-emitting device, which determines the growth of perovskite film directly. In this paper, the perovskite light-emitting diodes (PeLEDs) based on n-type nanocrystalline silicon oxide (n-nc-SiO<sub><i>x</i></sub>:H) electron injection layer are designed and realized. This novel electron injecting material is prepared by the plasma enhanced chemical vapor deposition (PECVD), and its smooth surface and matched energy band result in superior perovskite crystallinity and low electron injection barrier from the electron injecting layer to the emissive layer, respectively. However, the external quantum efficiency (EQE) of PeLED is as low as 0.43%, which relates to defects and leakage current due to the incomplete surface coverage of perovskite film. The fast exciton emission decay (< 10 ns) stems from strong non-radiative energy transfer to the trap states, and represents a big challenge in fabricating high-efficiency PeLEDs. In order to obtain desirable perovskite film morphology, an excessive proportion of methylammonium bromide (MABr) is incorporated into the perovskite solution, and a volume of benzylamine (PMA) is added into the chlorobenzene antisolvent. The perovskite films suffer low PLQY and short PL lifetime if only MABr or PMA is introduced. When the molar ratio of MABr is higher than 60%, the luminescence quenching arising from Joule heating is depressed by employing PMA, contributing to a higher PLQY (> 30%) and a longer carrier lifetime. The synergistic effect of MABr and PMA increase the coverage and reduce the trap density of perovskite film, inhibit the luminescence quenching in the annealing process, and thus facilitating the perovskite film with higher quality. Finally, the n-i-p PeLED exhibits green-light emission with a maximum current efficiency of 7.93 cd·A<sup>-1</sup> and a maximum EQE up to 2.13% is obtained. These facts provide a novel electron injecting material and a feasible process for implementing the PeLEDs. With further optimizing the perovskite layer and device configuration, the performance of n-i-p type PeLEDs will be improved significantly on the basis of this electron injection material.

Charge transport in isoindigo-dithiophenepyrrole based D-A type oligomers: A DFT/TD-DFT study for the fabrication of fullerene-free organic solar cells.

In this paper, we have designed a series of isoindigo-dithiophenepyrrole based oligomers with donor-acceptor architecture. The donor and acceptor units are joined by a thiophene linkage. We have substituted the 5,5'-positions of the isoindigo acceptor unit with different +I groups, viz., -CH3, -NH2, -SH, -OH, -OCH3, and -CH=CH2, and -I groups, viz., -F, -NO2, -CN, -COCH3, -COOH, and -CF3. We have studied the structural, charge injection, and transport properties employing the density functional theory (DFT) formalism. Our study explores that the presence of bulky substituents adversely affects these properties. Values of frontier orbital energies, ionization potentials, and electron affinities are calculated for each compound to predict the ease of charge injection from metal electrodes to these compounds. Most of our compounds show the ease of hole injection ability and show a large electron injection barrier. Computation of reorganization energies followed by the charge transfer integral and charge transfer rate have also been performed. Our findings reveal that compounds substituted with +I groups possess larger hole mobilities than the compounds with -I groups. Substitution of a dimer of compound 9 with -NO2 leads to the highest hole and electron mobility. Dipole moment values have also been calculated to study the charge transport properties. We have also computed the absorption properties of the compounds using the time-dependent DFT method. Our study indicates that absorption properties are changed by the attachment of substituents and can be tuned according to the requirements. Among the studied compounds, the -OCH3 substituted dimer (dimer 6) exhibits the largest bathochromic shift with a λ max of 554 nm. From this study, we can infer that our designed compounds are promising candidates for fabrication of optoelectronic devices.

Barrier formation at BaTiO3 interfaces with Ni and NiO

Barium Titanate and Ni-based multilayer ceramic capacitors have wide commercial applicability, and interfaces are critical to the overall device behavior as they can help control unwanted leakage currents. Here we make use of photoemission methods to investigate the electrostatic barriers formed at BaTiO3/Ni(O) interfaces to understand the implications for electron injection. We find the interface Fermi level in BaTiO3 to evolve smoothly during Ni deposition with a Schottky barrier height for electrons of 0.68 eV, whereas with NiO the Fermi level evolves rapidly with an electron injection barrier of 1.49 eV. In-situ poling shows the Schottky barrier at the BaTiO3/Ni interface is not significantly altered by ferroelectric polarization, consistent with the good screening of the Ni electrode. This study presents a direct quantitative measurement of the interface barrier heights and highlights the significance of the oxidation state of the electrode.

Functionalized Zinc Porphyrins with Various Peripheral Groups for Interfacial Electron Injection Barrier Control in Organic Light Emitting Diodes.

Here, we use a simple and effective method to accomplish energy level alignment and thus electron injection barrier control in organic light emitting diodes (OLEDs) with a conventional architecture based on a green emissive copolymer. In particular, a series of functionalized zinc porphyrin compounds bearing π-delocalized triazine electron withdrawing spacers for efficient intramolecular electron transfer and different terminal groups such as glycine moieties in their peripheral substitutes are employed as thin interlayers at the emissive layer/Al (cathode) interface to realize efficient electron injection/transport. The effects of spatial (i.e., assembly) configuration, molecular dipole moment and type of peripheral group termination on the optical properties and energy level tuning are investigated by steady-state and time-resolved photoluminescence spectroscopy in F8BT/porphyrin films, by photovoltage measurements in OLED devices and by surface work function measurements in Al electrodes modified with the functionalized zinc porphyrins. The performance of OLEDs is significantly improved upon using the functionalized porphyrin interlayers with the recorded luminance of the devices to reach values 1 order of magnitude higher than that of the reference diode without any electron injection/transport interlayer.

2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate as an effective electron injecting interlayer on indium-tin oxide cathode in inverted bottom-emission organic light-emitting diodes

2-Methyl-9,10-bis(naphthalen-2-yl)anthracene doped rubidium carbonate (MADN:Rb2CO3) is used as an effective electron injecting interlayer on an indium-tin oxide (ITO) cathode for inverted bottom-emission organic light-emitting diodes (IBOLEDs). At a Rb2CO3 doping concentration of 20% in MADN, the device exhibits enhanced characteristics, some of which are turn-on voltage, luminance at a given current density, and current efficiency. The attained performance is better than that of the device using lithium fluoride (LiF) as an n-type dopant. Space-charge-limited current acknowledges improved electrical properties of Rb2CO3 doped MADN. Ultraviolet and X-ray photoelectron spectroscopy investigation unveils an interfacial dipole layer induced by charge transfer between Rb2CO3 and ITO, leading to a lowered ITO work function and an electron injection barrier. The improved electron injection and transport capabilities contribute to better charge balance in IBOLED, thus resulting in advanced luminance efficiency. In addition, the morphology stability of organic films is also amended, which benefits long-term reliability under operationally induced thermal stress. Moreover, the effectiveness of using Rb2CO3:MADN as an electron injecting layer for IBOLEDs is superior to many of its alkali-based counterparts demonstrated in the literature, with high compatibility with different types of sophisticated ITO-based IBOLEDs.

Influence of Deposition Temperature and Source Gas in PE-CVD for SiO2 Passivation on Performance and Reliability of In–Ga–Zn–O Thin-Film Transistors

In this paper, we investigated the influence of both source gas and deposition temperature in plasma-enhanced chemical vapor deposition (PE-CVD) for a SiO2 passivation layer on the electrical properties and reliability of a bottom-gate In–Ga–Zn–O thin-film transistor (IGZO TFT). Two gas chemistries consisting of SiH4–N2O–N2 and tetraethoxysilane (TEOS)–O2 were utilized as the source gases for the PE-CVD SiO2 deposition, and the deposition temperature ( ${T}_{D}$ ) was adjusted from 180 °C to 380 °C. The TFT properties were basically identical for both gas chemistries at ${T}_{D}$ of 180 °C. When ${T}_{D}$ increased to 300 °C or higher, the TFTs with the SiO2 passivation deposited by SiH4–N2O–N2 gas chemistry (SiH4-SiO2) drastically changed from the transistor to the conductor. In contrast, the TFT with TEOS-SiO2 passivation maintained its TFT characteristics even at ${T}_{D}$ of 380 °C, despite the degradation of subthreshold characteristics and a negative shift of turn-on voltage were observed due to an electron injection barrier lowering as ${T}_{D}$ increased to 310 °C or higher. We also revealed that a stacked SiO2 passivation that is deposited at a different ${T}_{D}$ is an effective technique to improve the performance and reliability of the IGZO TFT.

Electron Injection on Metal/n-Doped Semiconducting Polymer

Efficient n-type doping was not established since the dopants dose not dissolve in same organic solutions of polymer semiconductors. Evaporative Spray Deposition using Ultra-dilute Solution (ESDUS) method enabled it recently. We have already reported efficient n-type doping of poly(2-methoxy-5-(2’-methyl-hexyloxy)-p- phenylenevinylene) (MEH-PPV: LUMO: 3.1 eV, HOMO: 5.2 eV). The high doping efficiency as much as 15% was realized. In organic devices composed of non-doped organic semiconductors, electron injection barrier is basically equal to the gap between LUMO of the organic semiconductor and work function of the el ectrode. It is still open question how the barrier is formed in the n-doped polymer/electrode. The metal/semiconductor junction of n-doped polymer has not been studied yet. In this research, we have fabricated electron only devices (EOD) of an n-doped polymer semiconductor using electrodes of Al and Ca. The electron injection from Al or Ca was examined.MEH-PPV (Mw = 40,000-70,000 Aldrich) and Cesium carbonate were used as a host polymer and an n-type dopant, respectively. The asymmetric EOD using Al for bottom and top electrodes and and a top Ca electrode having a lower work function (3.0 eV) were fabricated. The current-voltage (J-V) characteristics were measured in vacuum without breaking vacuum after the top electrode deposition. J-V characteristics of asymmetric EOD (Fig. 1), Al(50nm)/MEH-PPV:Cs2CO3 (110nm)/Ca(50nm) are fabricated. The current density was drastically increased as the doping concentration increased. The asymmetric EODs, current density in the forward bias was about 1 order of magnitude larger than that in reverse bias at low doping concentration at 0, 0.2, 2.0 wt%.However, the current density was almost overlapped in forward and reverse bias at the doping concentration of 10wt%. The disappearance of the rectification property suggests that the quantum tunneling takes place due to the very thin depletion layer at Al/MEH-PPV junction at the high doping concentration. In order to evaluate depletion layer width on Al/MEH-PPV junction, C-F measurement was carried out. As a result of the calculation, the depletion layer width of the 0.2 wt% doped device was 16.3 nm, the 2.0 wt% doped device was 9.3 nm, and the 10.0 wt% doped device was 3.3 nm. These results suggest that the depletion layer narrows as the doping concentration increases and the rectification property disappears in the 10 wt% doped device by quantum tunneling. The depletion layer width when quantum tunneling was observed in the p-type organic device, Au/ZnPc:0.3%F4-TCNQ/Au, was 5.2nm. Compared with this depletion layer width of 5.2 nm at metal/p-type organic semiconductor junction, it can be said that the value of 3.3 nm calculated this time is sufficiently narrow to observe quantum tunneling.

High-Efficiency Planar Hybrid Perovskite Solar Cells Using Indium Sulfide as Electron Transport Layer

For a high-performance perovskite solar cell (PSC), the electron transport layer (ETL) plays a prominent role in the transportation of photogenerated charge carriers from the perovskite layer to electrode. Herein, indium sulfide (In2S3) nanosheets are synthesized by solvent-thermal method; In2S3 ETL is prepared by spin-spraying technique, and planar PSC is thus fabricated. The morphology observation indicates that the as-prepared In2S3 ETL is compact, smooth, pinhole-free, and with an optimal thickness of 40 nm. The photoelectrical characterization reveals that, compared to TiO2 ETL, the In2S3 ETL has lower electron trap-state density, lower potential barrier for electron injection from the perovskite layer, higher electron mobility and electron extraction ratio at the In2S3/perovskite interface, smaller contact resistance, and charge recombination. The planar device fabricated with CH3NH3PbI3 perovskite and In2S3 ETL gains an impressive power conversion efficiency (PCE) of 18.83%, and the photovoltaic de...

Mechanistic Understanding of Improved Performance of Graphene Cathode Inverted Organic Light-Emitting Diodes by Photoemission and Impedance Spectroscopy.

Modification of multilayer graphene films was investigated for a cathode of organic light-emitting diodes (OLEDs). By doping the graphene/electron transport layer (ETL) interface with Li, the driving voltage of the OLED was reduced dramatically from 24.5 to 3.2 V at a luminance of 1000 cd/m2. The external quantum efficiency was also enhanced from 3.4 to 12.9%. Surface analyses showed that the Li doping significantly lowers the lowest unoccupied molecular orbital level of the ETL, thereby reducing the electron injection barrier and facilitating electron injection from the cathode. Impedance spectroscopy analyses performed on electron-only devices (EODs) revealed the existence of distributed trap states with a well-defined activation energy, which is successfully described by the Havriliak-Negami capacitance functions and the temperature-independent frequency dispersion parameters. In particular, the graphene EOD showed a unique high-frequency feature as compared to the indium tin oxide one, which could be explained by an additional parallel capacitance element.

Electrical characterization studies and doping effects of rubidium carbonate in organic layer by admittance spectroscopy

The doping effects and electrical characteristics of rubidium carbonate (Rb2CO3) in organic bipolar charge transport material 2-methyl-9,10-di(2-naphthyl) anthracene (MADN) has been investigated. Utilizing temperature-dependent admittance spectroscopy, the electron injection barrier (so-called activation energy) is verified to be reduced from 1.33 to 0.2878 eV by the incorporation of Rb2CO3 from 0 to 33 vol%. The precision of admittance spectroscopy is further proved by photovoltaic measurement. Higher mobility has achieved using space-charge-limited current (SCLC) determination. Consequently, these enhancements in electron injection and transport yield superior device performance for organic light-emitting diodes (OLEDs).

Origin of Positive Aging in Quantum-Dot Light-Emitting Diodes.

The phenomenon of positive aging, i.e., efficiency increased with time, is observed in quantum‐dot light‐emitting diodes (QLEDs). For example, the external quantum efficiency (EQE) of blue QLEDs is significantly improved from 4.93% to 12.97% after storage for 8 d. The origin of such positive aging is thoroughly investigated. The finding indicates that the interfacial reaction between Al cathode and ZnMgO electron transport layer accounts for such improvement. During shelf‐aging, the Al slowly reacts with the oxygen from ZnMgO, and consequently, leads to the formation of AlOx and the production of oxygen vacancies in ZnMgO. The AlOx interlayer reduces the electron injection barrier while the oxygen vacancies increase the conductivity of ZnMgO and, as a result, the electron injection is effectively enhanced. Moreover, the AlOx can effectively suppress the quenching of excitons by metal electrode. Due to the enhancement of electron injection and suppression of exciton quenching, the aged blue, green, and red QLEDs exhibit a 2.6‐, 1.3‐, and 1.25‐fold efficiency improvement, respectively. The studies disclose the origin of positive aging and provide a new insight into the exciton quenching mechanisms, which would be useful for further constructing efficient QLED devices.

Oxide Layer Enhances Photocurrent Gain of the Planar MAPbI3 Photodetector

AbstractEven though the current development of hybrid perovskite photodetectors makes them competitive with their inorganic analogs, a detailed fundamental understanding of their operating principles is still lacking. Here, the performance of planar polycrystalline perovskite photodetectors fabricated on interdigitated comb electrodes made from various metals is studied. It is demonstrated that the oxide layer on Cr and Pt electrodes increases the photo current gain by an order of magnitude. It is suggested that the gain enhancement originates from the hindered extraction of photogenerated holes and the migration of ions, which creates additional hole‐traps at interfaces. These effects reduce the barrier for electron injection and enable the passage of a larger number of electrons during the prolonged lifetime of photogenerated holes.

Spontaneous Silver Doping and Surface Passivation of CsPbI3 Perovskite Active Layer Enable Light-Emitting Devices with an External Quantum Efficiency of 11.2.

Lead halide perovskite nanocrystals are currently under intense investigation as components of solution-processed light-emitting devices (LEDs). We demonstrate LEDs based on Ag doped-passivated CsPbI3 perovskite nanocrystals with external quantum efficiency of 11.2% and an improved stability. Ag and trilayer MoO3/Au/MoO3 structure were used as cathode and anode, respectively, which reduce the electron injection barrier and ensure the high transparency and low resistance of the anode. Silver ions diffuse into perovskite film from the Ag electrode, as confirmed by the elemental mapping, the presence of Ag 3d peaks in the X-ray photoelectron spectrum, and the peak shift in the X-ray diffraction patterns of CsPbI3. In addition to doping, silver ions play the beneficial role of passivating surface defect states of CsPbI3 nanocrystals, which results in increased photoluminescence quantum yield, elongated emission lifetime, and improved stability of perovskite films.

Electronic Structures and Nanofilm Growth of 2,7-Dioctyl[1]Benzothieno[3,2-b]Benzothiophene on Black Phosphorus.

The interfacial electronic structure and morphology of nanofilm of 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on black phosphorus (BP) was investigated with photoemission spectroscopy (PES) and atomic force microscopy (AFM). The heterojunction of C8-BTBT/BP is a straddling one with a hole injection barrier of 1.41 eV and electron injection barrier of 2.43 eV from BP to C8-BTBT. There is a 0.18 eV interface dipole pointing from BP to C8-BTBT, which means a relative weak interaction of substrate BP and the C8-BTBT molecules. Volmer-Weber growth mode of C8-BTBT nanofilm on BP was confirmed and the C8-BTBT molecules adopt standing up configuration.

First Example of White Organic Electroluminescence Utilizing Perylene Ester Imides

AbstractUtilizing a series of bay‐annulated perylene ester imides (PEIs) doped in polyvinylcarbzole (PVK) as emissive layer, host‐guest organic light emitting diodes were fabricated and the electroluminescence behaviors of these devices have been explored. The devices exhibited emission from both PVK as well as PEI mainly due to the partial Förster resonance energy transfer from PVK to the emissive dopant. In order to achieve better device performance, two different electron transport layers, BPhen and TPBi were used. A remarkable improvement in the emission brightness and lower turn on voltage was observed, when TPBi was used as an electron‐transporting layer instead of BPhen. Incorporation of TPBi resulted in a lower electron injection barrier of TPBi‐PVK interface, which facilitates more electron injection into the emissive layer thus resulting in an increased recombination at a comparatively lower voltage. Also, the intensity of blue emission from PVK was enhanced in the case of TPBi based devices, resulting in an overall white electroluminescence, which is of high technological importance.