Doped Devices Research Articles

Efficient Triplet Harvesting via Hot Exciton Utilization in Solution Processed OLEDs Employing Tetraphenyl Buta‐1,3‐Diene Based AIE Emitters

AbstractHigh photoluminescence quantum yield (PLQY) especially in solid‐state together with harvesting radiative triplet excitons are essential to achieve efficient organic light‐emitting diodes (OLEDs). Herein, the aggregation induced emission (AIE) active tetraphenyl buta‐1,3‐diene (TPB) moiety has been employed and tactfully modified to obtain orthogonally oriented donor‐acceptor (D‐A‐π‐A‐D) type derivatives (namely, TPB‐CHO‐TPA and TPB‐CN‐TPA) which possess additionally the hybridized local and charge transfer (HLCT) type excited‐state. Moreover, computational studies have revealed the possibility of triplet harvesting through hot exciton mechanism in these designed emitters. These key features along with excellent solubility in most of the organic solvents have encouraged to utilize these as light emitting materials for solution processed non‐doped and doped OLED devices. The optimal OLED device using TPB‐CHO‐TPA exhibits yellow light emission (ELmax = 572 nm and CIEx,y = 0.48, 0.51) having maximum external quantum efficiency (EQEmax) of 7.6% with power and current efficiency of 6.1 lm W−1 and 8.9 cd A−1 where the calculated exciton utilization efficiency (EUE) approaches to 97%, indicating efficient triplet harvesting in electroluminescence process. This work signifies a novel design strategy for AIE‐based HLCT type emitters having efficient hot exciton utilization which can pave the way for future development of TPB based highly efficient OLED devices.

Glycolic acid doped PFN-Br as cathode interface to achieve high-efficiency in organic solar cells

Small compounds are often utilized to adjust the cathode interface of organic solar cells (OSCs) due to their low batch change, easy synthesis, unambiguous chemical structure, and low cost. In this work, the alcohol-soluble small molecule material Glycolic acid was doped into the electron transport material Poly(9, 9-bis(3′-(N, N-dimethyl)-N-ethylammoniumpropyl-2, 7-fluorene)-alt-2, 7-(9, 9-dioctylfluorene)) dibromide (PFN-Br) to modify the performance of the cathode interface layer (CIL). The CIL doped with Glycolic acid has better surface morphology, which is conducive to charge transport and extraction. In addition, the introduction of Glycolic acid improves the hydrophilicity of CIL, makes the metal electrode have good contact with CIL, and helps to improve the stability of the OSCs. Additionally, it suppresses the device's trap-assisted recombination and bimolecular recombination, hastening exciton dissociation and charge collection. As a result, the power conversion efficiency (PCE) of OSCs based on PM6: Y6 blend film has risen from 15.26 % to 15.91 %. After 312 hours of stability testing, the aforementioned doped devices still have device performance higher than standard device. Furthermore, based on PBDB-T: IT-M mix film, the PCE of the doped device and reference device was 11.29 % and 10.55 %, respectively. This study suggests that using the alcohol-soluble small-molecule material Glycolic acid can increase the organic solar cells' (OSCs') efficiency. This study provides a new method for manufacturing high-performance OSCs.

Enhancing Carrier Behavior via Controlled Molecular Film Formation Engineering Leads to Significant Improvement in Electroluminescence

The quality of organic thin films critically influences carrier dynamics in organic semiconductors. In neat/doped films, even tiny voids can be penetrated by water or oxygen molecules to create charge‐trap states called water/oxygen‐induced traps that significantly hinder carrier mobility. While the water/oxygen‐induced traps in non‐doped films and crystalline states have been investigated comprehensively, there is a lack of thorough examination regarding their properties in the doped state. Therefore, there is a high demand for a molecular design strategy that effectively modulates the molecular stacking behavior in doped films and practical devices and enhances the quality of these films. Herein, we proposed a versatile molecular design principle that enables the formation of "nano‐cluster" structures on both the surface and interior of doped films in target molecule 10‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐1'‐(4‐fluorophenyl)‐10H‐spiro[acridine‐9,9'‐xanthene] (DspiroO‐F‐TRZ), which is modified with a fluorophenyl group. These "nano‐cluster" structures exhibit more uniform shapes within doped films and effectively reduce defective state densities while enhancing carrier injection and transport properties, ultimately improving device performance. Notably, TADF‐OLED based on DspiroO‐F‐TRZ demonstrates nearly twice as much efficiency as its control counterpart due to contributions from 'nano‐cluster' structure enhancements toward improved electroluminescence performance.

Enhancing Carrier Behavior via Controlled Molecular Film Formation Engineering Leads to Significant Improvement in Electroluminescence.

The quality of organic thin films critically influences carrier dynamics in organic semiconductors. In neat/doped films, even tiny voids can be penetrated by water or oxygen molecules to create charge-trap states called water/oxygen-induced traps that significantly hinder carrier mobility. While the water/oxygen-induced traps in non-doped films and crystalline states have been investigated comprehensively, there is a lack of thorough examination regarding their properties in the doped state. Therefore, there is a high demand for a molecular design strategy that effectively modulates the molecular stacking behavior in doped films and practical devices and enhances the quality of these films. Herein, we proposed a versatile molecular design principle that enables the formation of "nano-cluster" structures on both the surface and interior of doped films in target molecule 10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1'-(4-fluorophenyl)-10H-spiro[acridine-9,9'-xanthene] (DspiroO-F-TRZ), which is modified with a fluorophenyl group. These "nano-cluster" structures exhibit more uniform shapes within doped films and effectively reduce defective state densities while enhancing carrier injection and transport properties, ultimately improving device performance. Notably, TADF-OLED based on DspiroO-F-TRZ demonstrates nearly twice as much efficiency as its control counterpart due to contributions from 'nano-cluster' structure enhancements toward improved electroluminescence performance.

Design and investigation of electrostatic doped heterostructure vertical Si(1-x)Gex/Si nanotube TFET

Researchers are inclining toward heterostructures suitable lattice matching, in Tunnel FETs to eliminate the difficulties of decreased On-Current, subthreshold swings, and ambipolar behavior. Nowadays, Electrostatic doping (ED) is a scrutinized substitute device for creating areas with a high electron or hole density to the conventional doped devices. This manuscript proposes an Electrostatic Doped Heterostructure Vertical Si(1-x)Gex/Si Nanotube Tunnel Field Effect with performance scanned by analyzing the different device parameters, considering the energy band diagram, concentrations of electrons, holes, potential, and electric field. In comparison to the Nanowire TFETs, the area, and rate of tunneling of the proposed device stand superior with a better ION/IOFF ratio of 1.56∗1013 and a lower OFF-current of about ∼10−18A/μm. The device exhibits a Drain current (IDS) of 2.39∗105A/μm. The architecture of the suggested device possessing Si(1-x)Gex/Si structure exhibits enhanced characteristics like improved steepness of the sub-threshold slope, ION/IOFF ratio, drain current, and lowered OFF-current.

High‐Efficiency Hybrid White Organic Light‐Emitting Diodes with Extremely Low Efficiency Roll‐Off and Superior Color Stability Enabled by an Emitting System with Imidazole‐Biphenyl Derivatives

AbstractHybride white organic light‐emitting diodes (WOLEDs) have experienced great success as a prospective technology for the new generation lighting source. Nevertheless, WOLEDs exhibiting excellent effciency and good color stability at high operation brightness are still rare. Herein, a simple but efficient blue molecule, pyrenoimidazole‐biphenyl (PPyIM), which exhibits promising external quantum efficiency (EQE) of 7.6% and 7.2% at the luminescence of 1000 −and 5000 cd m−2 in nondoped blue OLED, is first developed. And then, phenanthroimidazole‐biphenyl (PPIM) with analogous molecular skeleton of PPyIM is chosen as the host of phosphorescent dye PO‐01, and the resulting doped device achieves excellent EQE of 26.5% at the high luminescence of 5000 cd m−2. Furthermore, adopting PPyIM as nondoped blue emissive layer, the two‐color hybrid WOLED exhibites stable warm white emission with CIE coordinates of (0.454, 0.439), color rendering index (CRI) of 45, and correlated color temperature (CCT) of 2996 K. The maximum EQE reaches 23.5%, and the EQE still maintains 21.2% even at the luminance of 5000 cd m−2. Notably, this device exhibits exceptionally stable warm white emission, the CIE coordinates variation is only (0.004, 0.003) in the wide luminance range from 400 to 10000 cd m−2, representing the best outcome for hybrid WOLEDs to date.

Arylimidazole-terminated phenylene ethynylene molecules as organic luminescent materials

Three phenylene ethynylene derivatives substituted by arylimidazole groups (benzo[d]imidazole, phenanthro[9,10-d]imidazole and pyreno[4,5-d]imidazole) at both ends were successfully synthesized and characterized for organic electroluminescence devices. The photophysical, electrochemical, and thermal stability of the compounds were systematically investigated to reveal their structure-property relationships. All compounds presented a X-shaped structure, and exhibited excellent thermal stability and intense emission in solution and solid states. Furthermore, the solution-processed doped devices using the blend of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) with the phenylene ethynylene derivatives as emitting layers emitted deep-blue emission with maximum external quantum efficiency (EQEmax) of 0.63 % for the benzo[d]imidazole-terminated derivative and blue emission with EQEmax of 1.93 % and 1.45 % for the phenanthro[9,10-d]imidazole- and pyreno[4,5-d]imidazole-terminated derivatives, respectively, suggesting that these compounds have a great potential as the organic emitters for deep-blue and blue devices.

Efficient and ultra-high luminance orange-red organic light emitting diode (OLED) based on triphenylamine-benzothiadiazole-phenoxazine hybrid molecule with hybrid local and charge-transfer (HLCT) characteristic

Due to the energy gap law, red emission needs relatively narrow energy gap, thus the nonradiative transition rate (knr) grows exponentially and eventually impacts the materials fluorescent efficiency. Here, an orange-red emission donor-acceptor-π-donor (D-A-π-D’) material N, N-diphenyl-4-(7-(4-(10-phenyl-10 H-phenoxazin-3-yl) phenyl) benzo [c] (Huang et al., 2019; Park et al., 2008; Caspar et al., 1982) [1,2,5] thiadiazol-4-yl) aniline (TBphPP) was designed and synthesized. Introducing a benzene π-bridge between the strong donor 10-phenyl-10H-phenoxazin (PPOX) and acceptor 2,1,3-benzothiadiazole (BTZ) not only is able to stretch the molecular conjugation so as to increase the proportion of LE state in hybrid local and charge-transfer (HLCT) state but also increase the overlap area of the electron cloud to improve luminous efficiency. As a result, the non-doped organic light-emitting diode (OLED) of TBphPP exhibited high luminance of 17,886 cd m−2 and relatively high exciton utilization efficiency (EUE) of 44 % with a standard red electroluminescent peak at 620 nm. Importantly, the optimized doped device based on TBphPP achieved high performance that the maximum external quantum efficiency (EQEmax) was up to 9.86 % with a higher EUE of 66.2 % and the efficiency roll-off (ηroll-off) at 100,000 cd m−2 was only 3.55 %. Simultaneously, it has reached ultra-high luminescence of 180,583 cd m−2, high current efficiency of 29.02 cd A−1 and power efficiency of 16.47 l m W−1. To our knowledge, the TBphPP device with such ultra-high luminance and high efficiency is one of the best performance orange-red materials based on HLCT characteristic.

A comparative study on the gas sensing performance of SnO2 and GO-SnO2 sensor devices.

Using Modified Hummer’s technique, eco-friendly carbon derivative (GO) nanoparticles were obtained from polyethylene terephthalate (PET) precursor. Nanocomposite of GO-SnO2 and undoped SnO2 were synthesized using the coprecipitation method. The as-prepared nanoparticles were subjected to diverse analytical processes employing Transmission electron microscopy (TEM) to study the internal morphological properties of the nanoparticles. Energy dispersive X-ray spectroscopy (EDX) was used to examine elemental quantifications of the nanopowders. Fourier-transform infrared (FTIR) spectroscopy was used to analyze bond structures and functional groups. Dynamic responses of various gas sensor devices to 20 ppm concentrations of methane (CH4) and hydrogen (H2) were investigated as a function of time at room temperature. The GO-SnO2 nanocomposite sensing device demonstrated an ideal detection response with values of 5.00 and 5.08, corresponding to methane and hydrogen analyte gases. The doped SnO2 sensor device outperformed the pure SnO2, accounting for the GO-SnO2 > SnO2 order. Regarding the target gases, the synthesized nanocomposite demonstrated stability and selectivity in the following order of magnitude: H2 > CH4. The GO doping effect was found to have introduced surface defects, increased pores, and enabled more oxygen-active sites to be formed on the sensor device’s surface for dynamic gas sensing response, providing a comparatively enhanced sensor response.

Effective N‐Doping of Non‐Fullerene Acceptor via Sequential Deposition Enables High‐Efficiency Organic Solar Cells

AbstractCharge transport in the active layer, which can be effectively modulated by molecular doping of organic semiconductors, significantly affects the photovoltaic performance of organic solar cells (OSCs). However, it is difficult to control the dopant distribution in the bulk heterojunction (BHJ) films, which hinders efficient doping in OSCs. Herein, an effective n‐doping strategy is developed via sequential deposition (SD) of D18 donor and doped acceptor. The favorable vertical component distribution in SD films helps to optimize carrier transport pathways. The SD method confines the n‐dopant N‐DMBI to the acceptor layer, allowing positive effects of molecular doping. Consequently, the doped SD device exhibits superior charge transport with suppressed charge recombination, lower trap density, and enhanced charge extraction compared to the undoped one, resulting in a high power conversion efficiency of 19.55% for D18/L8‐BO binary OSCs. In addition, the doping does not affect the thermal stability of the devices, with the doped SD device retaining over 90% of its initial efficiency after 1200 h of heating at 80 °C. The universality of the SD doping method is also verified in other non‐fullerene acceptor systems. These results demonstrate the great potential of SD doping strategy for building high‐performance OSCs with enhanced charge transport.

Low-cost dopant-free fluoranthene-based branched hole transporting materials for efficient and stable n-i-p perovskite solar cells

It has been widely recognized that hole transporting materials (HTMs) play a key role in the rapid progress of perovskite solar cells (PVSCs). However, common organic HTMs such as spiro-OMeTAD not only suffer from high synthetic costs, but also usually require the additional chemical doping process to improve their hole transport ability, which unfortunately induces the terrible stability issue. Therefore, it is urgent to develop low-cost dopant-free HTMs for efficient and stable PVSCs. In this work, we have successfully developed a new class of efficient dopant-free fluoranthene-based HTMs (TPF1–5) with quite low lab synthetic costs by combining donor-acceptor and branched structure designs. The detailed structure-property study revealed that tuning the twisted arms at different substitution sites would regulate the intermolecular interactions and film-forming ability, thereby significantly affecting the performance of the HTMs. By applying these HTMs in conventional PVSCs, the dopant-free TPF1-based devices not only achieved the best efficiency of 21.76%, which is comparable to that of the doped spiro-OMeTAD control devices, but also showed much better operational stability, which maintained over 87% of the initial efficiency under maximum power point tracking after 1038 h.

Regulating SnZn defects and optimizing bandgap in the Cu2ZnSn(S,Se)4 absorption layer by Ge gradient doping for efficient kesterite solar cells

In recent years, the primary reasons for low efficiency Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have been attributed to SnZn defects and related defect clusters, as well as the balance of absorption layer bandgap for short-circuit current density (Jsc) and open-circuit voltage (Voc). Ge gradient has been theoretically proven to be an effective strategy to change traditional flat bandgap structure and suppress SnZn defects and related defect clusters for improving the device performance of CZTSSe solar cells. However, the potential of Ge gradient has not been fully verified. In this work, Ge doping effectively reduces the formation of SnZn defects and [2CuZn + SnZn] defect clusters in the CZTSSe absorption layer. In addition, it can be found that the construction of the V-type bandgap is the best solution for balancing between Voc and Jsc. By using the bandgap grading strategy, the disparity between the recombination barrier of the junction and the optical bandgap's minimum value is widened, thereby obtaining a large Voc. The V-type doped device has the highest efficiency when Voc is 0.45 V, which can reach 8.03%. This Ge graded substitution method provides an alternative absorption layer structure for improving Voc and the preparation of future high-efficiency kesterite photovoltaic devices.

Non‐uniform doping dependent electrical parameters of dual‐metal gate all around junctionless accumulation‐mode nanowire FET (DMGAA‐JAM‐NWFET)

AbstractThis paper presents an analytical analysis of a dual‐metal gate all around junctionless accumulation‐mode nanowire FET (DMGAA‐JAM‐NWFET) possessing a horizontal‐like non‐uniform doping profile. The 2‐D electrostatic potential distribution is evaluated using Poisson's equation under the applicable boundary conditions. Also, the impact of straggle length parameter and the peak doping concentration upon the device behavior is also examined. For authenticating the obtained analytical outcomes, TCAD simulations were also performed. Both the results were contrasted and found to be in good agreement. The outcomes obtained for non‐uniform doped DMGAA‐JAM‐NWFET are also compared with that of uniformly doped DMGAA‐JAM‐NWFET and finer electrical characteristics were noticed for non‐uniformly doped device.

New-type 2D iodine materials with tunable electronic transport impacted by the doping of nonmetal elements

Special structures and good characteristics make 2D iodine structures more appealing and valuable at high pressures. The electrical transport of such 2D iodine structures is theoretically studied here, taking the doping of nonmetal elements into account. Most doped devices show considerably greater equilibrium conductance than the original device. Devices with the dopants in lower atomic numbers show higher conductance. The transmission spectrum all around EF can be improved by the doping of nonmetal elements. Essentially, DDOS can well explain the variations in electron transmission probability caused by the doping of nonmetal atom for most doped devices, serving as one main inherent factor in electron transport. The influence of nonmetal dopants on transmission eigenstates varies according to the main group, essentially depending on the number of transferring channels and the strength of transmission eigenstates. Influenced by the bias, the conductance of such innovative devices fluctuates but with varied amplitudes. Every doping mode can enhance the conductance by applying the bias and such biases for all doping modes must cover lower biases. Unlike the dopants in larger atomic numbers, the devices with the dopants in smaller atomic numbers show much difference in size between the voltage interval that enhances and the voltage interval that weakens. The current grows linearly with bias. Nonmetal doping enables the current to increase at low voltages and decrease at high voltages, compared with the undoped device. The improved and attenuated effect on the current is good for doped devices with nonmetal elements in smaller atomic numbers, but poor in higher atomic numbers. These discoveries contribute significantly to our understanding of the effects of defects and elemental adsorption on electrical characteristics and give strong evidence for the use of new-type 2D iodine materials in controlled electronics and sensors.

Highly efficient deep blue electroluminescent material with high and towards balanced carrier transmission performance based on hybrid local and charge-transfer (HLCT) excited state

Deep blue electroluminescent materials play a decisive role in organic light-emitting diodes (OLEDs). Herein, three novel deep blue molecules based on hybridized local and charge-transfer (HLCT) excited state were reported, namely CZFPY, CZFPI and TPAFPI. Single-crystal analysis of TPAFPI shows abundant intermolecular interactions, which restricts molecular rotation and suppresses structural vibrations, promotes TPAFPI achieved a high photoluminescence quantum yield (PLQY) up to 72 % in solid state. More importantly, these abundant intermolecular interactions significantly increase its carrier mobilities, with hole and electron mobilities as high as 1.2 × 10−5 cm2 V−1 s−1 and 5.4 × 10−6 cm2 V−1 s−1, respectively. Consequently, the non-doped OLED based on TPAFPI achieved excellent device performance, the maximum current efficiency (CEmax) is 12.4 cd/A, the maximum power efficiency (PEmax) is 14.0 lm W−1, the maximum external quantum efficiency (EQEmax) is 7.2 % with high device stability, the efficiency roll-off is only 4.7 % at 1000 cd m−2. What is more, the doped device of TPAFPI exhibits a higher EQEmax of 10.1 % with a higher color purity, the Commission International de L’Eclairage (CIE) coordinate is (0.15, 0.06), matching the National Television Standards Committee (NTSC) standard. The comprehensive performance of TPAFPI-based doped device is at the highest level in the field of deep blue OLEDs (0.06 ≤ CIEy ≤ 0.09).

Synthesis and characterization of Ag-doped CdS quantum dots for enhanced photovoltaic performance of quantum dot sensitized solar cells

In this work, Ag-doped and undoped CdS quantum dots (QDs) were prepared via successive ionic layer adsorption and reaction (SILAR) technique, followed by their characterization. The synthesized QDs were employed in the devices based on iodide/triiodide (I−/I3−) and polysulfide (Sx2−/S2−) electrolytes, while carbon (C) and platinum (Pt) were used as counter electrodes (CEs). The structural properties of the synthesized QDs were examined using X-ray diffraction (XRD), while to analyze the elemental composition of the samples, energy-dispersive X-ray (EDX) spectroscopy technique was employed. To study absorption properties, UV–Visible spectroscopy was performed. The influence of Ag on passivation of defects in CdS QDs was investigated via photoluminescence spectroscopy. Photovoltaic performance and impedance spectroscopic measurements on the fabricated QDSSCs were made under an AM1.5G illumination and dark, respectively. The photovoltaic studies on the devices revealed an increase of efficiency by 131 %, 161 %, 151 %, and 93 % for Ag–CdS QDs/Iodolyte/Pt, Ag–CdS QDs/Polysulfide/Pt, Ag–CdS QDs/Iodolyte/C, Ag–CdS QDs/Polysulfide/C type devices, respectively. The doped device with a polysulfide electrolyte and C as counter electrode (CE) revealed superior performance, exhibiting an efficiency of 1.72 %, followed by the doped polysulfide-based device with Pt as CE, revealing 1.67 % efficiency. The stability test conducted on the fabricated devices demonstrated a long-term stability for the doped device containing polysulfide electrolyte and C as CE, retaining 80 % of its initial efficiency for 12 days, and then falling to 0 % in 22 days. Moreover, the impedance spectroscopic measurements revealed lowest series resistance (Rs) and Series Capacitance (Cs) for the superior performance device.

Rational design of hybridized local and charge-transfer (HLCT) emitters towards blue OLEDs with high luminance and low efficiency roll-off

Organic blue emitters have been get more and more attention by scientists and industries in the field of organic light-emitting diodes (OLEDs). The design of efficient blue emitters, especially deep-blue ones, is still a challenge because of their intrinsic wide band-gaps and unbalanced carrier mobilities. Herein, two donor‒π‒acceptor (D‒π‒A) type molecules with phenanthro[9,10-d]imidazole (PI) as A and pyridinyl as π-bridge were designed and synthesized by fine-turning the D moieties, namely mPTPA and mP3PCZ, respectively. Theoretical calculation and single-crystal analysis showed that there exist intramolecular hydrogen bond (IHB) interactions inducing small torsion angles between pyridinyl and adjacent phenyls. The rigid 9-phenyl-9H-carbazole (PCZ) and IHB interactions makes mP3PCZ exhibiting planar configuration along the long-axis of the molecule, which could increase the orbital overlap and oscillator strength (fos). The solvatochromic effect manifested that both two emitters have hybridized local and charge-transfer (HLCT) characteristics, and the excited state of mP3PCZ exhibited LE-dominated HLCT state which is beneficial for high photoluminescence efficiency. Ultimately, the non-doped devices based on mPTPA and mP3PCZ achieved maximum luminance larger than 12000 cd m−2. Furthermore, the doped device based on mP3PCZ exhibited maximum external quantum efficiency of 5.14% with low efficiency roll-off, and with the corresponding deep-blue Commission international de l’éclairage (CIE) coordinate of (0.166, 0.085).

Improved detection performance of self-driven InZnO / p-GaN heterojunction UV photodetector by lanthanum doping

By using the sol-gel spin-coating method, La-InZnO films with different La (0 at%, 2 at%, 4 at%, and 6 at%) doping concentrations were grown on p-GaN / sapphire film templates, and self-driven p-GaN / n-ZnO heterojunction ultraviolet (UV) detectors were prepared. The effects of La doping concentration on the microstructure, optical, and electrical properties of synthesized La-InZnO films were studied. In addition, the optical sensing characteristics and photoelectric response performance of four p-n heterojunction UV detectors were compared. La doping can decrease the content of oxygen vacancies. It also reduces the carrier concentration and mobility of the films. At zero bias voltage, the 2 at% doped device has the best performance, with a peak responsivity of 46 mA/W at 366 nm, a high spectral selectivity full width at half maximum (FWHM) of only 6.92 nm, and a fast response with the rise and decay times of 1.15 ms and 2.42 ms, respectively. This study demonstrates a feasible method for improving the performance of self-driven heterojunction UV detectors.

Achieving Efficient Near‐Ultraviolet/Deep‐Blue OLEDs and Sensitized Narrowband Green/Yellow OLEDs Utilizing Emitters with Planarized Intramolecular Charge Transfer

AbstractHigh‐quality near‐ultraviolet/deep‐blue organic emitters are urgently needed but still rare. Here, three V‐shape donor‐acceptor‐donor (D‐A‐D) emitters based on pyrazine cores, namely, VDMP‐PhCz, VDMP‐36PhCz, and VDMP‐TPA, are designed and synthesized. Their doped devices using a high‐polar host show remarkable electroluminescence (EL) performances with maximum external quantum efficiency (EQE) values up to 7.37%, 7.55%, and 9.03%, and corresponding CIE coordinates of (0.160,0.040), (0.161,0.039), and (0.149,0.072), respectively. Supported by theoretical calculations and experimental results, the high EL performances of these emitters are achieved by their planarized intramolecular charge transfer (PLICT) features, high triplet‐excitons utilization from “hot exciton” channels, and high horizontal dipole orientations. Furthermore, these PLICT‐based emitters can also function as efficient hosts for green or yellow multi‐resonance (MR) narrowband emissive guests, providing high EQEs of over 32% with alleviated efficiency roll‐offs.

Donor–Acceptor Molecules with Locked sp3 Carbon Link for Highly Efficient Near Ultraviolet Organic Light‐Emitting Diodes

AbstractTo achieve high‐performance near ultraviolet (NUV) organic light‐emitting diodes (OLEDs), highly stable and fluorescent emitters with good triplet utility are essential. The challenge in making such molecules stems from the fact that a wide bandgap and strong luminescence are two conflicting requirements. Herein, a new strategy is proposed for NUV emitters featuring donor–acceptor moieties linked by a rigid sp3 carbon atom to weaken the conjugation and reduce nonradiative processes. The resultant emitters exhibit excellent NUV luminescence, high thermal and electrochemical stabilities, and hybridized local and charge‐transfer excited‐state characteristics. A nondoped device emits NUV light (414 nm, Commission Internationale de L'eclairage coordinates [CIEx,y] = 0.157, 0.058) with a maximum luminance, current efficiency, and external quantum efficiency (EQE) of 7979 cd m−2, 2.53 cd A−1, and 6.60%, respectively. The device also shows a small efficiency roll‐off of 6.8% at 1000 cd m−2. A doped device acquires a high efficiency and color purity with a maximum EQE of 7.64%, CIEx,y of (0.158, 0.049), and emission peak of 406 nm, representing one of the best values among NUV OLEDs. This research provides an effective method to achieve high‐performance NUV OLEDs and also offers flexibility in material design.