Doped Devices Research Articles

Solution-Processable Anion-doped Conjugated Polymer for Nonvolatile Organic Transistor Memory with Synaptic Behaviors

Brain-inspired synaptic transistors have been considered as a promising device for next-generation electronics. To mimic the behavior of a biological synapse, both data processing and nonvolatile memory capability are simultaneously required for a single electronic device. In this work, a simple approach to realize a synaptic transistor with improved memory characteristics is demonstrated by doping an ionic additive, tetrabutylammonium perchlorate (TBAP), into an active polymer semiconductor without using any extra charge storage layer. TBAP doping is first revealed to improve the memory window of a derived transistor memory device from 19 to 32 V (∼68% enhancement) with an on/off current ratio over 103 at VG = -10 V. Through morphological analysis and theoretical calculations, it is revealed that the association of anion with polymers enhances the charge retention capability of the polymer and facilitates the interchain interactions to result in improved memory characteristics. More critically, the doped device is shown to successfully mimic the synaptic behaviors, such as paired-pulse facilitation (PPF), excitatory and inhibitory postsynaptic currents, and spike-rate dependent plasticity. Notably, the TBAP-doped device is shown to deliver a PPF index of up to 204% in contrast to the negligible value of an undoped device. This study describes a novel approach to prepare a synaptic transistor by doping conjugated polymers, which can promote the future development of artificial neuromorphic systems.

Stimuli-Responsive Aggregation-Induced Delayed Fluorescence Emitters Featuring the Asymmetric D-A Structure with a Novel Diarylketone Acceptor Toward Efficient OLEDs with Negligible Efficiency Roll-Off.

Multifunctional luminescent materials with aggregation-induced delayed fluorescence (AIDF) are capable of suppressing concentration-caused emission quenching and exciton annihilation when used as organic light-emitting diode (OLED) emitters. In this contribution, three stimuli-responsive AIDF luminogens, pipd-BZ-PXZ, pipd-BZ-PTZ, and pipd-BZ-DMAC, featuring a D-A asymmetric framework based on a fused N-heterocycle diarylketone acceptor (imid-azo[1,2-a]pyridin-2-yl(phenyl)methanone pipd) are designed and synthesized. Interestingly, pipd-BZ-PTZ forms two different kinds of crystals (G-crystal and O-crystal) with distinct intermolecular interactions between pipd moieties. The G-crystal with a looser packing mode presents significant morphology-dependent stimuli-responsive behavior with a shifted emission wavelength of 56 nm. Generated by a strong intramolecular charge transfer effect, pipd-BZ-PXZ and pipd-BZ-PTZ exhibit orange to red emission in solution and neat films. Both nondoped and doped devices are fabricated for comparison. Nondoped devices present moderate performance with external quantum efficiencies and current efficiency that reach 7.04% and 19.86 cd A-1, respectively, and the corresponding efficiency roll off at 1000 cd m-2 is as small as 2.3%, which is among the best records of AIDF-OLEDs with an emission wavelength over 570 nm. Doped devices show better performance with corresponding efficiencies of up to 55.41 cd A-1 and 15.77%.

Engineering substrate doping in bulk planar junctionless transistor: Scalability and variability study

In this work two dimensional sentaurus simulations are used to study the impact of substrate doping on scalability and the variability of the bulk planar junctionless transistor (BPJLT). The results shows that, although increasing substrate doping density in BPJLT reduces the off-state current, subthreshold slope and the drain induced barrier lowering, the on-state current of the device is almost constant. To improve digital logic circuit performance of nanoscale BPJLT, novel δ-layer BPJLT (δ-BPJLT) is being proposed by incorporating p-type δ- layer below the uniformly doped device layer containing source, channel and the drain regions of BPJLT. It has been found that, the δ-layer below the device layer leads to reduction in the off-state current, process induced variability and the short-channel effects of the BPJLT. This is mainly because of the screening effect due to δ-layer under the device layer which significantly reduces the variations induced because of random dopant fluctuations.

Large rectification ratio induced by nitrogen and boron doping in adjacent armchair graphene nanoribbons

The rectification behavior of two and three separated armchair graphene nanoribbons (AGNRs) which one of them plays the role of channel and others play the role of side gates is investigated. The tight-binding density functional approach (DFTB) and non-equilibrium Green function method (NEGF) are employed for calculations. The nitrogen (N) and boron (B) atoms are used to dope the side gates. The results show that these devices have low threshold voltage and their rectification ratios are higher than one doped AGNR device, with the maximum value of 3.18 × 108. Also, without doping the channel, it can become to n-type or p-type semiconductor, only by doping the side gates. The current-voltage characteristics of these devices are similar and have little dependence on side gates width.

Photo- and electro-luminescence properties of the organic bipolar molecules containing phenothiazine and phenanthoimidazole moieties

Three new organic bipolar molecules containing phenothiazine and phenanthoimidazole moieties, 10-butyl-3-(phenanthroimidazol-2-yl)phenothiazine (PI-PTZ), 10-butyl-3-((4-(tert-butyl)phenyl)phenanthroimidazol-2-yl)phenothiazine (PPI-PTZ) and 10-butyl-3,7-bis((4-(tert-butyl)phenyl)phenanthroimidazol-2-yl)phenothiazine (PPI-PTZ-PPI), were successfully synthesized for organic light-emitting devices. Their thermal stabilities, photophysical and electrochemical properties were investigated systematically. These compounds exhibited strong blue or blue-green emissions with photoluminescence quantum efficiency (Φf) of 41.48 %, 40.51 % and 61.52 % in chloroform solutions, while their Φf in the solid thin films decreased to 37.53 %, 34.05 % and 47.77 %, respectively. Furthermore, the vacuum-processed doped devices based on these compounds were fabricated, in which the devices based on the compound PPI-PTZ-PPI exhibited the best electroluminescence performance with a maximum brightness of 30,180 cd/m2, a maximum current efficiency of 10.65 cd/A and a maximum external quantum efficiency (EQE) of 4.0 %.

Highly Emissive Dinuclear Platinum(III) Complexes.

Dinuclear Pt(III) complexes were commonly reported to have short-lived lowest-lying triplet states, resulting in extremely weak or no photoluminescence. To overcome this obstacle, a new series of dinuclear Pt(III) complexes, named Pt2a-Pt2c, were strategically designed and synthesized using donor (D)-acceptor (A)-type oxadiazole-thiol chelates as bridging ligands. These dinuclear Pt(III) complexes possess a d7-d7 electronic configuration and exhibit intense phosphorescence under ambient conditions. Among them, Pt2a exhibits orange phosphorescence maximized at 618 nm in degassed dichloromethane solution (Φp ≈ 8.2%, τp ≈ 0.10 μs) and near-infrared (NIR) emission at 749 nm (Φp ≈ 10.1% τp ≈ 0.66 μs) in the crystalline powder and at 704 nm (Φp ≈ 33.1%, τp ≈ 0.34 μs) in the spin-coated neat film. An emission blue-shifted by more than 3343 cm-1 is observed under mechanically ground crystalline Pt2a, affirming intermolecular interactions in the solid states. Time-dependent density functional theory (TD-DFT) discloses the lowest-lying electronic transition of Pt2a-Pt2c complexes to be a bridging ligand-metal-metal charge transfer (LMMCT) transition. The long-lived triplet states of these dinuclear platinum(III) complexes may find potential use in lighting. Employing Pt2a as an emitter, high-performance organic light-emitting diodes (OLEDs) were fabricated with NIR emission at 716 nm (η = 5.1%), red emission at 614 nm (η = 8.7%), and white-light emission (η = 11.6%) in nondoped, doped (in mCP), and hybrid (in CzACSF) devices, respectively.

Inverted pyramid Er3+ and Yb3+ Co-doped TiO2 nanorod arrays based perovskite solar cell: Infrared response and improved current density

In this study, a Yb3+, Er3+ co-doped TiO2 inverted pyramid nanorod (NR) array and a compact TiO2 film are simultaneously fabricated as the mesoporous support layer and electron-blocking layer, respectively, by a one-pot hydrothermal method. The scanning electron microscopy results show that the incorporation of Er3+ and Yb3+ causes changes not only in the growth rate of the NRs, but also in the TiO2 NR morphology. The Er3+, Yb3+ co-doped TiO2 NRs exhibit an inverted pyramidal morphology, which is beneficial for perovskite permeation and light utilization. Notably, the Er3+, Yb3+ co-doping causes changes in the band gap of TiO2 and leads to 25% increase in the current density. The electrochemical impedance spectroscopy results show that the device based on the doped TiO2 NRs has a higher recombination resistance and a lower transfer resistance than those of the undoped device, and thereby, the doped device exhibits a lower electron recombination rate. In addition, the upconversion Er and Yb co-doped device exhibits 25% higher current density and 17% higher photon-to-electron conversion efficiency, as revealed by the J-V test results. Moreover, the optimized efficiency of the TiO2 NR array-based perovskite solar cell is determined to be 10.02%. Furthermore, the Er and Yb co-doped device exhibits a near-infrared response, an efficiency of 0.1% is achieved under infrared light (800–1100 nm) irradiation. This upconversion material can widen the photovoltaic responses of solar cells into the near-infrared region and improve the utilization of sunlight.

Reversible writing of high-mobility and high-carrier-density doping patterns in two-dimensional van der Waals heterostructures

A key feature of two-dimensional materials is that the sign and concentration of their carriers can be externally controlled with techniques such as electrostatic gating. However, conventional electrostatic gating has limitations, including a maximum carrier density set by the dielectric breakdown, and ionic liquid gating and direct chemical doping also suffer from drawbacks. Here, we show that an electron-beam-induced doping technique can be used to reversibly write high-resolution doping patterns in hexagonal boron nitride-encapsulated graphene and molybdenum disulfide (MoS2) van der Waals heterostructures. The doped MoS2 device exhibits an order of magnitude decrease of subthreshold swing compared with the device before doping, whereas the doped graphene devices demonstrate a previously inaccessible regime of high carrier concentration and high mobility, even at room temperature. We also show that the approach can be used to write high-quality p–n junctions and nanoscale doping patterns, illustrating that the technique can create nanoscale circuitry in van der Waals heterostructures. An electron beam technique can be used to write high-resolution doping patterns in graphene and MoS2 van der Waals heterostructures, and could allow doped circuit designs to be created.

Hydrogen bond-modulated molecular packing and its applications in high-performance non-doped organic electroluminescence

Suitable intermolecular hydrogen bonding enables the formation of a fixed 3D supramolecular framework and suppresses the exciton nonradiative decays and quenching.

Efficient TADF-OLEDs with ultra-soluble Copper(I) halide complexes containing non-symmetrically substituted bidentate phosphine and PPh3 ligands

High efficiency copper(I) halide complexes containing rigid diphosphine ligand have attracted much attention. However, rigid bidentate phosphine ligands were rarely reported so far and limited to structural symmetric diphosphines. Here, a series of four-coordinate mononuclear copper(I) halide complexes containing non-symmetrically substituted bidentate phosphine and PPh3 Ligands, CuX(dpts)(PPh3) [dpts = 2-trimethylsilyl-3,4-bis(diphenylphosphine)thiophene, X = I (1), Br (2), Cl (3)] and in comparison to CuX(dppt)(PPh3) [dppt = 3,4-bis(diphenylphosphino)thiophene, X = I (4), Br (5), Cl (6)], were synthesized, and their molecular structures and photophysical properties were investigated. The introduction of trimethylsilyl group into diphosphine ligand, not only greatly improves the solubility of the complexes, but also quantum efficiency, and fine-tunes the emission color as well. These complexes exhibit intense bluegreen to yellowish green emissions in powder state at room temperature and have peak wavelengths at 485–535 nm with microsecond lifetimes (τ = 4.8–48.9 μs, Φ = 0.03–0.52). The emission of the complexes 1–6 mainly originates from MLCT (metal to ligand charge transfer), XLCT (halide to ligand charge transfer) and intraligand transitions. Solution-processed, nondoped and doped devices of complex 2 exhibit yellow green emission with CIE(x,y) of (0.43, 0.51). The nondoped device gives a maximum external quantum efficiency (EQE) of 7.74% and a maximum luminance of 234 cd/m2. These promising results open the door to solution-processed, efficient TADF (thermally activated delayed fluorescence) OLED (organic light-emitting diode) devices with ultra-soluble and abundant copper emitters.

Asymmetrically twisted phenanthrimidazole derivatives as host materials for blue fluorescent, green and red phosphorescent OLEDs

The electroluminescent properties of asymmetrically twisted phenanthrimidazole derivatives comprised of fluorescent anthracene or pyrene unit namely, 1-(1-(anthracen-10-yl)naphthalen-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (ANSPI), 1-(1-(pyren-1-yl) naphthalene-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (PNSPI), 4-(2-(4-(anthracen-9-yl) styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (ASPINC) and 4-(2-(4-(pyren-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PSPINC) for blue OLEDs have been analyzed. The asymmetrically twisted conformation interrupt π-conjugation effectively results in deep-blue emission. The pyrene containing PSPINC based non-doped blue device (476 nm) shows maximium efficiencies (current efficiency (ηc)-4.23 cd/A; power efficiency (ηp)-2.86 lm/W; external quantum efficiency (ηex)-3.48%: CIE (0.16, 0.17) at 3.10 V. Among the doped blue devices, An(PPI)2:ASPINC shows high efficiencies (ηc-12.13 cd/A; ηp-5.98 lm/W; ηex-6.79%; L-23986 cd m−2; EL-458 nm) at 3.15 V with CIE (0.15, 0.17) than An(PPI)2:PSPINC based device which is inconsistent with non-doped device performances. The green and red PhOLEDs show higher efficiencies with Ir(ppy)3: ASPINC (ηc-50.6 cd/A; ηp-53.4 lm/W; ηex-17.0%; L-61581 cd m−2; EL-501 nm, CIE (0.31, 0.60) at 3.32 V and (bt)2Ir(dipba): ASPINC (ηc-15.2 cd/A; ηp-16.5 lm/W; ηex-14.5%; L-13456 cd m−2; EL-610 nm), CIE (0.63, 0.36) at 3.20 V, respectively. The complete energy transfer between the host and dopant molecules improved the efficiency of PHOLEDs.

Structural Modification of Doped Tunnel Field Effect Transistor for Enhanced Conduction Current and Lower Subthreshold Swing

The material solubility in the source region and abrupt source/channel junction profile are the major concern which is responsible for the improvement of the electrical characteristics of conventional physical doped tunnel field effect transistor (PD-TFET). For this, an additional negatively polarised electrode is mounted in P+ (source) – N (channel) – N+ (drain) structure over the source region to overcome material solubility. This improves the electrical characteristics of the device. Along with this, we have implanted a low workfunction metal layer (ML) in the oxide layer under the gate electrode for creating more abruptness at the junction to improve the subthreshold swing (SS) of the device. Thus, the proposed concept improves the DC/RF performance of the doped TFET device. Further to this, the optimization of metal layer workfunction and misalignment of metal layer in TFET have been performed to get optimum device characteristics. In addition to this, for the suppression of ambipolar behaviour, gate electrode is shorted from the drain side. Due to short length of gate electrode tunneling barrier width at the drain/channel junction increases, hence the tunneling probability decreases which reduces the ambipolar current to parasitic current. Shortening of gate electrode also improves the RF performance.

Functionalized coumarin derivatives containing aromatic-imidazole unit as organic luminescent materials

Three new coumarin derivatives containing aromatic-imidazole unit (i.e., benzo[d]imidazole, phenanthro[9,10-d]imidazole and pyreno[4,5-d]imidazole), 3-(1-phenyl-1H-benzo[d]imidazole-2-yl)-7-(diethylamino)coumarin (BI–C), 3-(1-(4-(tert-butyl)phenyl)-1H-phenanthro[9,10-d]imidazole-2-yl)-7-(diethylamino)coumarin (PI–C) and 3-(9-(4-(tert-butyl)phenyl)-9H-pyreno[4,5-d]imidazole-10-yl)-7-(diethylamino)coumarin (PyI-C), were successfully prepared for organic light-emitting devices. These compounds show good thermal properties and strong emissions from greenish-blue to green lights owing to the extended π-conjugation of the rigid polyaromatic imidazole skeleton, and have high photoluminescence quantum efficiency of 94%, 97% and 98% in chloroform solutions. Among these compounds, the doped organic light-emitting device fabricated from the compound PI-C exhibited the maximum luminous efficiency of 6.07 cd/A and maximum EQE of 2.78%.

Extraction and conversion of exhaust heat from automobile engine in to electrical energy

The ever increasing demand for energy is leading to rapid depletion of our resources. Inspite of the advancement in renewable technology. It is therefore important that the available energy conserved and utilized efficiently. In automobiles about 60-70% of energy out of the total heat supplied by fuel is dissipated as waste heat and just about 30 to 40 percent is transformed into useful mechanical work [1-3].This paper focus on the recovery and utilization of waste heat into useful electrical energy by using Seebeck effect where in Thermoelectric Generators (TEG) are placed on the exhaust surface for converting heat directly into electrical energy. Thermoelectric generators are highly doped semiconductor solid state devices. The voltage throughput of the thermoelectric generator is given to a dc super lift converter circuit. The output of the super lift converter is used for battery charging.

Modeling of Fringing Capacitances of Ion-Implanted Double-Gate Junctionless FETs Using Conformal Mapping

This article reports an analysis of the fringing capacitances of an ion-implanted double-gate (DG) junctionless (JL) field-effect transistors (FETs). The actual nonintegrable Gaussian function of the ion-implanted channel has been replaced by an integrable Gaussian-like vertical channel doping profile to model the fringing capacitances of the DG JLFET. The boundary conditions for the source and drain depletion regions of the uniformly doped channel has been modified according to the nonuniformly doped channel using the conformal mapping technique. In this method, the gate-oxide capacitance is transformed to the source and drain fringing capacitances using an empirical multiple coefficient ${m}$ whose value is determined by matching the model result with the ATLAS TCAD simulation data for their best fitting. It is shown that unlike the uniformly doped device, the fringing capacitances are different for the front and back gates. Furthermore, the nonlinear bias-dependent potential profile along the channel leads to different fringing capacitances at the source and drain of the proposed device. The dependence of the fringing capacitances (and ${m}$ ) on the doping profile and bias conditions are investigated in detail. Accordingly, analytical expressions for the fringing capacitances are extracted. The model results are verified by the TCAD simulations.

Effect of Ir(pq)2acac doping on CBP in phosphorescence organic light-emitting diodes

Doping is one of the most powerful methods amongst the various performance improvement ways. Doping affects the energy levels of the host layer by the energy level of the dopant. This allows the energy bandgap to be adjusted to a desired level and thus generates light corresponding to that energy level. Alternatively, it can act as an energy barrier between the interfaces to change the flow of carriers. In this study, the voltage dependences of undoped and doped devices were observed. Bis(2-phenylquinoline) iridium(III) (acetylacetonate) (Ir(pq)2acac) was doped in 4,4′-N, N′-dicarbazole-biphenyl (CBP) as the emission layer. The light intensity changes with the doping concentration, and the efficiency was also studied. When a high voltage was applied, the effect of triplet-triplet annihilation (TTA) adversely affected the electron-hole recombination. We analyzed the optimal operating conditions and the effect of doping concentration on OLEDs.

Performance limits of vertical GaN of conventional doped pn and natural polarization superjunction devices

We have determined and evaluated the specific on-resistance (Ron,sp) vs breakdown voltage (BV) trade-off limits of vertical GaN-based conventional doped pn superjunction (SJ) and natural polarization superjunction (PSJ) devices using analytical models and numerical simulations. We have obtained much better performance on the vertical natural polarization superjunction devices based on the AlGaN/GaN and AlInN/GaN heterostructures instead of the conventional superjunction devices with alternating doped p/n pillars. Our results show that the drift-region Ron,sp of vertical GaN-based superjunction devices is one to more than four orders of magnitude lower than the 1D limit of GaN conventional unipolar devices at the same BV. For 1 and 10 kV devices, the optimized specific on-resistance of the drift region is about 10 and 300 times lower for conventional superjunction devices, but 1000 and 20 000 times lower for natural polarization superjunction devices.

Through-space charge transfer in luminophore based on phenyl-linked carbazole- and phthalimide moieties utilized in cyan-emitting OLEDs

Two new carbazole-containing aromatic imides were synthesized by three-step synthetic pathway with the moderate yields up to 76%. The compounds were investigated theoretically. TD-DFT computational studies revealed low singlet-triplet energy differences. The compounds were found to have relatively high thermal stability with 5% mass loss temperatures in the range of 280–310 °C. Phthalimide-based compound exhibited aggregation-induced emission enhancement and thermally activated delayed fluorescence with photoluminescence quantum efficiency of 20% in the solid state. Structure-properties relationship of this compound was investigated and it was found that charge-transfer through space mechanism is responsible for the emission. Series of green-emitting doped and non-doped electroluminescent devices were fabricated based on the carbazole-phthalimide derivative were fabricated to reveal best-performing mCP-doped device demonstrating maximum external quantum efficiency of 2.4% with current efficiency of 6.6 cd/A and power efficiency of 4.0 lm/W with maximum brightness of 8300 cd/m2.

Preparation and luminescence properties of isoquinoline-nucleated polycyclic aromatics

Two isoquinoline-nucleated polycyclic aromatic compounds, 4,5-diphenyl-7H-dibenzo[de,g]quinolin-7-one (A) and 3,4-diphenyl-6H-phenanthro[3,4,5-defg]quinolin-6-one (B), were synthesized in high yields through three-component reaction of phenanthrene diketone or pyrene diketone, ammonium acetate and 1,2-diphenylethyne in one-pot. Their structures, thermal stabilities, photophysical properties and energy levels are investigated systematically. Both compounds emit very weak fluorescence in acetone, but their luminescence intensity increased significantly when the water content reaches 50% for A and 40% for B, exhibiting aggregation-induced emission (AIE) characteristics, and showing that the AIE effect of the compound A is stronger than that of the compound B. The vacuum-processed doped devices based on the compound B showed green emission with a maximum brightness of 2162 cd/m2, a maximum current efficiency of 2.97 cd/A and a maximum external quantum efficiency (EQE) of 2.23%.

Efficient Passivation with Lead Pyridine‐2‐Carboxylic for High‐Performance and Stable Perovskite Solar Cells

AbstractStability has become the main obstacle for the commercialization of perovskite solar cells (PSCs) despite the impressive power conversion efficiency (PCE). Poor crystallization and ion migration of perovskite are the major origins of its degradation under working condition. Here, high‐performance PSCs incorporated with pyridine‐2‐carboxylic lead salt (PbPyA2) are fabricated. The pyridine and carboxyl groups on PbPyA2 can not only control crystallization but also passivate grain boundaries (GBs), which result in the high‐quality perovskite film with larger grains and fewer defects. In addition, the strong interaction among the hydrophobic PbPyA2 molecules and perovskite GBs acts as barriers to ion migration and component volatilization when exposed to external stresses. Consequently, superior optoelectronic perovskite films with improved thermal and moisture stability are obtained. The resulting device shows a champion efficiency of 19.96% with negligible hysteresis. Furthermore, thermal (90 °C) and moisture (RH 40–60%) stability are improved threefold, maintaining 80% of initial efficiency after aging for 480 h. More importantly, the doped device exhibits extraordinary improvement of operational stability and remains 93% of initial efficiency under maximum power point (MPP) tracking for 540 h.