High External Quantum Efficiency Research Articles

Manipulating the excited states from charge-transfer to hybridized local and charge-transfer towards high-performance blue electroluminescence

Manipulating the excited states of organic luminescent materials can efficiently improve the utilization of both singlet and triplet excitons for developing high-performance organic light-emitting diodes (OLEDs), but the issue remains difficult due to the lack of well-controlled ways. Here, we proposed a molecular design strategy of excited state manipulation from charge-transfer (CT) to hybridized local and charge-transfer (HLCT) via adjusting the cyano position on pyridine acceptor. The meta-substituted PyAn4CN is mainly composed of a CT component, while the para-substituted PyAn5CN is endowed with a HLCT component. On further extending the conjugation of PyAn5CN by inserting a benzene unit between the pyrene and anthracene core, the HLCT character is preserved in PyPhAn5CN, accompanied by a faster radiative decay. Consequently, the vacuum-evaporated OLEDs exhibit blue electroluminescence (EL) with the emission peaks in the range of 455–460 nm and high external quantum efficiency (EQE) up to 7.52%, together with well-suppressed efficiency roll-offs of 0.8% and 3.7% at the luminance of 100 and 1000 cd m-2, respectively. More importantly, the solution-processed device shows an excellent performance with EQE of 6.49%, which is one of the best results in the solution-processed HLCT OLEDs. Our results clearly indicate that the formation of HLCT state is an efficient way to realize high-efficiency blue electrofluorescence.

Hybridization of short-range and long-range charge transfer excited states in multiple resonance emitter

Multiple resonance (MR) thermally activated delayed fluorescence emitters have been actively studied as pure blue dopants for organic light-emitting diodes (OLEDs) because of excellent color purity and high efficiency. However, the reported MR emitter, 2,5,13,16-tetra-tert-butylindolo[3,2,1-jk]indolo[1′,2′,3′:1,7]indolo[2,3-b]carbazole (tDIDCz) based on bis-fused indolocarbazole framework could not demonstrate efficient triplet-to-singlet spin crossover. In this work, we report two isomeric MR emitters designed to promote triplet exciton harvesting by reconstructing the electronic structure of tDIDCz. To manage excited states, strong electron donors were introduced at the 2,5-/1,6-position of tDIDCz. As a result, 2,5-positions managed tDIDCz shows long-range charge transfer characteristics while preserving the MR nature. Quantum chemical calculation demonstrates direct spin-orbit coupling by long-range charge transfer and spin-vibronic coupling assisted reverse intersystem crossing by short-range charge transfer simultaneously contribute to triplet-to-singlet spin crossover. Consequently, high performance blue OLED recorded a high external quantum efficiency of 30.8% at a color coordinate of (0.13, 0.13).

Novel Spiro Core‐Based Hole Transport Materials for Stable Deep‐Blue OLEDs with LT95 Over 420 h

AbstractFlexible, lightweight, and cost‐effective organic light‐emitting diodes (OLEDs) show great promise for use in displays and lighting applications. However, creating highly efficient and stable deep‐blue OLEDs remains a challenge due to a lack of efficient functional materials, specifically hole transport materials (HTM). In this report, two new spiro‐HTMs are introduced with fluorene (FBP‐SFX) or dibenzofuran (DBF‐SFX) peripheral substituents. This study finds that the DBF‐SFX variant produces highly efficient deep‐blue OLEDs with a narrow emission (full‐width at half‐maximum FWHM of 25 nm) and the highest external quantum efficiency (EQE) of 33.2% among the FBP‐SFX (12.2%) and NPB (11.9%) variants. The superior performance of DBF‐SFX is attributed to its deeper highest occupied molecular orbital level (HOMO) and small trap density, which results in reduced band‐edge offset, lower turn‐on voltages, and balanced charge carrier densities. Importantly, the blue fluorescence OLED with DBF‐SFX displays exceptional device stability with LT95 over 420 h with an initial luminance of 1000 cd m−2. This is due to the stronger bond dissociation energy (BDE) and suppressed Exciton–Polaron Annihilation (EPA) using the dibenzofuran substituent. This work demonstrates a new HTM design approach using a spiro‐core architecture and dibenzofuran substituents to create efficient and long‐lasting deep‐blue OLEDs.

Multi-active region AlGaN UV LEDs with transparent tunnel junctions

In this work, we demonstrate two-junction UV LEDs enabled by transparent tunnel junctions. Low voltage-drop tunnel junctions were realized in Al0.3Ga0.7N layers through a combination of high doping and compositional grading. Capacitance and current–voltage measurements confirmed the operation of two junctions in series. The voltage drop of the two-junction LED was 2.1 times that of an equivalent single-junction LED, and the two-junction LED had higher external quantum efficiency (147%) than the single junction.

High‐Performance Self‐Assembled ZnO Nanowrinkle Network Structured Photodetectors

Herein, the effect of prebake temperature on the surface structure of zinc oxide (ZnO) nanowrinkle structures formed in a sol–gel growth process for UV photodetection is demonstrated. The sol–gel solutions are spin‐coated on glass and c‐plane sapphire substrates, and the resulting ZnO films are subjected to prebake and crystallization processes at 800 °C for an hour. In the sol–gel process, the prebake process is crucial in forming the nanowrinkle structure on the surface of the ZnO film. The maximum nanowrinkle structure of ZnO film is achieved at the prebake temperature of 150 °C. In addition to the formation of the optimized nanowrinkle structure, the UV response of the photodetector is further enhanced through the prebake temperature control. The nanowrinkle network structure significantly improves the optical absorbance and photoluminescence characteristics of the ZnO film, leading to high photocurrent, photoresponsivity, and external quantum efficiency for UV light. The results demonstrate the potential of sol–gel‐derived ZnO photodetectors with nanowrinkle network structures for UV sensing applications.

Space-confined through-space charge-transfer emitters based on CN-substituted fluorene acceptors: Design, synthesis, and thermally-activated delayed fluorescence

Space-confined through-space charge-transfer (TSCT) emitters have been extensively explored for developing thermally-activated delayed fluorescence (TADF), but their donor/acceptor units need to be expanded for tuning the emission properties. Herein we report TSCT-TADF emitters 1–3 by chemically fixing cyano-substituted fluorenes as the acceptors. For 1 and 2, 9H-fluorene-2,5-dicarbonitrile (2,5-CN-FL) and 9H-fluorene-2,7-dicarbonitrile (2,7-CN-FL) are used as the acceptors, respectively, and 1,3,6,8-tetramethyl-9H-carbazole is used as the donor. For emitter 3, 2,7-CN-FL and benzo[5,6][1,4]oxazino[2,3,4-kl]phenoxazine are used as the acceptor and the donor, respectively. Single-crystal structures and theoretical calculations reveal close, cofacial donor/acceptor alignments and thus effective TSCT in 1–3. In doped 2,8-bis(diphenylphosphoryl) dibenzo[b,d]furan films, emitters 1 and 2 show similar blue-green emission centered at around 510 nm, and emitter 3 shows yellow emission centered at 562 nm, with photoluminescent efficiencies at 0.66−0.76. Compared to emitters 1 and 2, emitter 3 shows much faster reverse intersystem crossing due to its much smaller singlet-triplet energy splitting. Organic light-emitting diodes (OLEDs) using 1–3 as the emitters afford blue-green or yellow electroluminescence with high external quantum efficiencies up to 14.9%. The work demonstrates that cyano-substituted fluorenes with a planar and rigid geometry are promising acceptors for developing TSCT-TADF emitters for OLED applications.

Enhanced Charge Balance for Efficient Electroluminescence from Cesium Copper Halides.

Cesium copper halides have the advantages of high photoluminescence quantum efficiency and good stability, making them attractive for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs). However, due to their shallow conduction band and the lack of electron transport layers compatible with it, it remains a great challenge to achieve charge balance in LED devices. This drawback manifests as the accumulation of holes at the interface between the emitting layer and electron transport layer, resulting in nonradiative recombination. Here, we demonstrate an effective approach to address this issue by suppressing hole injection, which is realized through modification of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) layer with polyethylenimine. This leads to cesium-copper-halide LEDs with a high external quantum efficiency of 5.6%, representing an advance in device architecture for efficient electroluminescence from cesium copper halides.

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.

High‐Performance Narrowband OLED with Low Efficiency Roll‐Off Based on Sulfur‐Incorporated Organoboron Emitter

AbstractMulti‐resonance (MR) based organoboron emitters exhibiting high‐efficiency narrowband thermally activated delayed fluorescence (TADF) have become a critical material component for constructing high‐performance organic light‐emitting diodes (OLEDs) with high color purity and high color gamut. However, most of the MR‐TADF devices suffer from severe efficiency roll‐off at high current density due to the relatively large singlet–triplet splitting energy, long excited state lifetime, and slow reverse intersystem crossing rate (k RISC). Herein, by utilizing a sulfur atom‐fused donor unit, 7H‐benzo[4,5]thieno[2,3‐b]carbazole, an organic boron emitter (BTC‐BNCz) capable of high efficiency and low efficiency roll‐off narrowband TADF emission is developed. Benefitting from the heavy atom effect of the sulfur atom, kRISC up to 1.6 × 105 s−1 is achieved, which could greatly reduce the undesired quenching effect. Consequently, the OLED using BTC‐BNCz as dopant exhibits high external quantum efficiency (EQE) of 27.0% with full width at half maximum (FWHM) of 35 nm. Moreover, by utilizing a TADF material with a high horizontal dipole ratio as assistant host, outstanding device performance is achieved with a maximum EQE of 35.2% and FWHM of 37 nm, featuring slow efficiency roll‐off.

Postdeposition Halide Exchange for Achieving Deep-Blue Perovskite Light-Emitting Diodes: The Role of the Organic Cations in the Chloride Source.

Postdeposition halide exchange has been a popular strategy for tuning the emission wavelength of metal halide perovskites and is particularly attractive in achieving deep-blue perovskite light-emitting diodes (PeLEDs), where the quality of the emissive layer is largely limited by the low solubility of chlorides in perovskite precursor solution. In this work, the halide exchange strategy isexamined for deep-blue PeLEDs, with a focus on understanding the role of the organic cations of the halide salt (i.e., the chloride source for ion exchange) in modifying the properties of the perovskite films and consequently the PeLED performances. By comparatively investigating the treatment effects of two model systems, namely phenethylammonium chloride and 2,2-diphenylethylammonium chloride (DPEACl), it isfound that although the two chlorides produce highly similar photoluminescence properties of the perovskite films, they create different landscapes for current flow in the PeLEDs. In particular, the bulky branch-structured DPEA cations exhibit minimal disturbance to the perovskite grains while providing highly effective inter-grain void filling and thus leakage current blocking, leading to 3D perovskite-based PeLEDs with a record high peak external quantum efficiency of 6.4% at 462nm. The study highlights the importance of organic cation selection in the halide exchange processes for PeLEDs.

Ultraefficient Non‐Doped Deep Blue Fluorescent OLED: Achieving a High EQE of 10.17% at 1000 cd m−2 with CIEy<0.08

AbstractThe pursuit for efficient deep blue material is an ever‐increasing issue in organic optoelectronics field. It is a long‐standing challenge to achieve high external quantum efficiency (EQE) exceed 10% at brightness of 1000 cd m−2 with a Commission International de L'Eclairage (CIEy) <0.08 in non‐doped organic light‐emitting diodes (OLEDs). Herein, this study reports a deep blue luminogen, PPITPh, by bonding phenanthro[9,10‐d]imidazole moiety with m‐terphenyl group via benzene bridge. The non‐doped OLED based on PPITPh exhibits an exceptionally high EQE of 11.83% with a CIE coordinate of (0.15, 0.07). The EQE still maintains 10.17% at the brightness of 1000 cd m−2, and even at a brightness as high as 10000 cd m−2, an EQE of 7.5% is still remained, representing the record‐high result among non‐doped deep‐blue OLEDs at 1000 cd m−2. The unprecedented device performance is attributed to the reversed intersystem crossing process through hot exciton mechanism. Besides, the maximum EQE of orange phosphorescent OLED with PPITPh as host is 32.02%, and remains 31.17% at the brightness of 1000 cd m−2. Such minimal efficiency roll‐off demonstrates that PPITPh is also an excellent phosphorescent host material. The result offers a new design strategy for the enrichment of high‐efficiency deep blue luminogen.

Implementation of Photosynaptic and Electrical Memory Functions in Organic Nano‐Floating‐Gate Transistors via a Perovskite‐Nanocrystal‐Based Nanocomposite Tunneling Layer

An organic nano‐floating‐gate transistor (ONFGT) with both photosynaptic and electrical memory functions is developed using a perovskite (CsPbBr3) NC‐insulating polymer (polystyrene; PS) nanocomposite and CsPbBr3 NCs as the tunneling and floating gate layers, respectively. The introduction of the CsPbBr3 NCs–PS nanocomposite layer improves the photoresponsivity of the ONFGT under ultraviolet–visible irradiation, resulting in an increase in both the photocurrent and the light‐to‐dark current ratio by 10−8 A and 104 orders of magnitude, respectively. It also exhibits high responsivity (0.804 A W−1) and external quantum efficiency (249.3%) under 400 nm irradiation. Furthermore, the photosynaptic characteristics of the ONFGT under visible‐light irradiation are investigated. To mimic biological nervous systems, the photocurrent of the device is dynamically modulated by varying the light intensity and duration. Notably, an increase in synaptic weight is observed under repeated photonic stimulations, as shown by changes in synaptic weight with each light pulse. Also, the ONFGT exhibits excellent nonvolatile memory characteristics in the dark, displaying a hysteresis window value of 2.9 V for a gate double sweep under ±5.0 V. Consequently, the perovskite NCs–insulating polymer nanocomposite tunneling layer is crucial for enabling photoresponsivity and memory characteristics in nano‐floating‐gate transistors, making them suitable for multifunctional electronic devices.

Creating an efficient and tunable near-infrared emission by using [Mg2+-Sn4+] chemical unit co-substitution in Ga2O3:Cr3+ phosphor

NIR phosphor-converted light-emitting diode (NIR pc-LED) has attracted many attentions for its promising applications in biomedical imaging, night vision, spectroscopy, and many other fields, while the discovery of broadband NIR phosphors with high external quantum efficiency (EQE) remains a challenge. Herein, a series of efficient and tunable broadband NIR-emitting Ga1.97-2xMgxSnxO3:0.03Cr3+ phosphors were synthesized via [Mg2+-Sn4+] substituting [Ga3+-Ga3+] in Ga2O3:Cr3+ system. As increase of substituting ratio x, a significant red-shift in the emission spectra from 726 to 793 nm with a full width at half maximum (FWHM) extended from 121 to 167 nm can be observed. All the samples have an EQE above 40% under 450 nm excitation; and the excitation peak in the blue light region remains unchanged, enabling these materials to be efficiently excited by blue LEDs. Finally, a NIR pc-LED device was fabricated by integrating the optimized Ga1.77Mg0·1Sn0·1O3:0.03Cr3+ phosphor on a blue LED chip, which exhibits a high NIR output power of 33.41 mW with a photoelectric conversion efficiency of 12.01% under a drive current of 100 mA. These results indicate that the obtained NIR phosphors may have potential in NIR pc-LEDs applications.

Engineering the Macrocyclic Donor Structures towards Deep-Blue Thermally Activated Delayed Fluorescence Emitters.

Deep-blue thermally activated delayed fluorescence (TADF) molecules present promising potential in organic light-emitting diodes (OLEDs), especially for display applications. Here, an efficient molecular engineering approach to modifying the donor or acceptor features of the D-π-A-configured TADF molecules for deep-blue emission is reported. By introducing oxygen and sulfone as a bridge unit onto the macrocyclic donor, two emitters, c-ON-MeTRZ and c-NS-MeTRZ, are synthesized and characterized, respectively. The reduced donor strength of c-ON-MeTRZ and c-NS-MeTRZ as compared to that of the model molecule c-NN-MeTRZ leads to blue-shifted emissions with high photoluminescence quantum yields (PLQYs) and retains TADF characters, while the new emitter c-NN-MePym with the most blue-shifted emission only exhibits a pure fluorescent nature because of the electron-accepting feature of pyrimidine that is insufficient for inducing the TADF property. In the presence of macrocyclic donors, these new emitters show high horizontal dipole ratios (Θ// = 85-89%), which are beneficial for improving the light out-coupling efficiency. Deep-blue TADF OLEDs incorporating c-ON-MeTRZ as an emitter doped in the mCPCN host achieves a high maximum external quantum efficiency (EQEmax) of 30.2% together with 1931 Commission Internationale de I'Eclairage (CIE) coordinates of (0.14, 0.13), while the counter device employing c-NS-MeTRZ as a dopant gives EQEmax of 15.4% and CIE coordinates of (0.14, 0.09). The EQEmax of c-ON-MeTRZ- and c-NS-MeTRZ-based devices can be significantly improved to 34.4 and 29.3%, respectively, with a polar host DPEPO, which stabilizes the charge transfer (CT) S1 state to give lower ΔEST for improving the reverse intersystem crossing process. The efficient TADF character, high PLQYs, and high anisotropic emission dipole ratios work together to render the superior electroluminescence (EL) efficiencies. Based on the detailed characterizations of physical properties, theoretical analyses, and comprehensive study on the corresponding devices, a clear structure-property-performance relationship has been successfully established to verify the effective molecular design strategy of modulating the macrocyclic donor characters for efficient deep-blue TADF emitters.

Doping-Free High-Performance Photovoltaic Effect in a WSe2 Lateral p-n Homojunction Formed by Contact Engineering.

Two-dimensional transition metal dichalcogenides (TMDs) are promising materials for semiconductor nanodevices owing to their flexibility, transparency, and appropriate band gaps. A variety of optoelectronic and electronic devices based on TMDs p-n diodes have been extensively investigated due to their unique advantages. However, improving their performance is challenging for commercial applications. In this study, we propose a facile and doping-free approach based on the contact engineering of a few-layer tungsten di-selenide to form a lateral p-n homojunction photovoltaic. By combining surface and edge contacts for p-n diode fabrication, the photovoltaic effect is achieved with a high fill factor of ≈0.64, a power conversion efficiency of up to ≈4.5%, and the highest external quantum efficiency with a value of ≈67.6%. The photoresponsivity reaches 283 mA/W, indicating excellent photodiode performance. These results demonstrate that our technique has great potential for application in next-generation optoelectronic devices.

Ultralow Dark Current Room‐Temperature Infrared Photodetector Based on InSb Nanosheets/MoS2 Van der Waals Heterostructure

As a narrow‐bandgap semiconductor, InSb is widely used in infrared (IR) detection due to its excellent performance and other characteristics such as ultrahigh electron mobility, extremely high quantum efficiency, and robust chemical properties. Herein, an ultralow dark current room‐temperature IR photodetector based on InSb nanosheets (NSs)/MoS2 flakes van der Waals (vdW) heterostructure is presented. Benefiting from a large surface‐to‐volume ratio and phonon scattering suppressed on the nanostructure, InSb NSs devices have high photosensitivity and low dark current density (16.67 A cm−2). To further suppress the dark current, a vdW heterojunction composed of InSb NSs and MoS2 is fabricated. When the InSb NSs/MoS2 vdW heterostructures’ photodetector work on a photovoltaic model (zero‐bias operation), the device shows a dark current density as low as 0.12 A cm−2 at room temperature, exhibiting a high external quantum efficiency (EQE) of 3.6 × 102%, the responsivity of 3.8 A W−1, and detectivity of 1.2 × 109 cm Hz1/2 W−1 under 1310 nm laser illumination. These results demonstrate that InSb NSs vdW heterostructure is a feasible scheme to realize InSb room‐temperature IR detection.

Carbene-stabilized enantiopure heterometallic clusters featuring EQE of 20.8% in circularly-polarized OLED

Bright and efficient chiral coinage metal clusters show promise for use in emerging circularly polarized light-emitting materials and diodes. To date, highly efficient circularly polarized organic light-emitting diodes (CP-OLEDs) with enantiopure metal clusters have not been reported. Herein, through rational design of a multidentate chiral N-heterocyclic carbene (NHC) ligand and a modular building strategy, we synthesize a series of enantiopure Au(I)-Cu(I) clusters with exceptional stability. Modulation of the ligands stabilize the chiral excited states of clusters to allow thermally activated delayed fluorescence, resulting in the highest orange-red photoluminescence quantum yields over 93.0% in the solid state, which is accompanied by circularly polarized luminescence. Based on the solution process, a prototypical orange-red CP-OLED with a considerably high external quantum efficiency of 20.8% is prepared. These results demonstrate the extensive designability of chiral NHC ligands to stabilize polymetallic clusters for high performance in chiroptical applications.

Visible–infrared dual-band detection with a polarization sensitivity based on GeSe/Ge heterojunction field effect transistor

Electronic and optoelectronic devices based on two-dimensional (2D)/three-dimensional (3D) semiconductor heterostructures, combining their respective advantages, have attracted wide attention. In this work, we fabricate a mixed-dimensional GeSe/Ge heterojunction field effect transistor (HJFET), which combines high carrier mobility of 2D GeSe and near-infrared detection of 3D bulk Ge. A significant on/off ratio of 5 × 102 and a transconductance of 0.23 μS are obtained, indicating a convincing gate control ability. Under 532 nm illumination, the HJFET exhibits an excellent photoresponse with high responsivity, detectivity, and external quantum efficiency (88.4 A/W, 2.25 × 1012 Jones, and 3280%), and it also can detect the infrared light of 1550 nm due to the absorption of Ge gate. The photogenerated electrons at 532 nm flow to Ge back gate when HJFET works at the reverse voltage bias, which prolongs the lifetime of photogenerated holes in the GeSe channel, thus increasing photocurrent and obtaining better the detection properties. Additionally, the transistor also exhibits polarization-sensitive behavior with a dichroic ratio of 2.37, which can be attributed to the strong anisotropic absorption property of GeSe in armchair and zigzag directions. These results indicate that the device has promising potential as a multifunctional optoelectronic unit, including on/off characteristic, broadband photodetection, and polarization sensitivity.

Dimethyl-dihydroindenocarbazole-anthracene-phenanthroimidazole based hybridized local and charge-transfer molecules as efficient nondoped deep-blue emitters for highly efficient fluorescent organic light-emitting diodes

The pursuit of hybridized local and charge transfer (HLCT) excited state-based emitters is a promising strategy to achieve high external quantum efficiency in blue organic light-emitting diodes (OLEDs). Two isomeric dimethyl-dihydroindenocarbazole-anthracene-phenanthroimidazole-based emissive molecules (PhAnsIn and PhAnoIn) were designed and explored based on the HLCT scheme. All molecules possessed the HLCT excited-state characters, according to the photophysical investigation and density functional theory calculations. Consequently, PhAnsIn and PhAnoIn showed good blue emission with peaks at 457 and 464 nm and photoluminescence quantum yield of 80.6% and 56.5% in neat films, respectively. The fabricated blue OLEDs with PhAnsIn and PhAnoIn as emitters also realized the corresponding blue emission with electroluminescence peaks at 458 and 457 nm, respectively. The nondoped devices based on PhAnsIn and PhAnoIn exhibited maximum external quantum efficiencies of 8.2% and 8.5% with CIE coordinates of (0.14, 0.12) and (0.14, 0.11), respectively.

Color Stable Deep Blue Multi-Resonance Organic Emitters with Narrow Emission and High Efficiency.

The development of highly efficient and deep blue emitters satisfying the color specification of the commercial products has been a challenging hurdle in the organic light-emitting diodes (OLEDs). Here, deep blue OLEDs with a narrow emission spectrum with good color stability and spin-vibronic coupling assisted thermally activated delayed fluorescence are reported using a novel multi-resonance (MR) emitter built on a pure organic-based molecular platform of fused indolo[3,2,1-jk]carbazole structure. Two emitters derived from 2,5,11,14-tetrakis(1,1-dimethylethyl)indolo[3,2,1-jk]indolo[1',2',3':1,7]indolo[3,2-b]carbazole (tBisICz) core are synthesized as the MR type thermally activated delayed fluorescence emitters realizing a very narrow emission spectrum with a full-width-at-half-maximum (FWHM) of 16nm with suppressed broadening at high doping concentration. The tBisICz core is substituted with a diphenylamine or 9-phenylcarbazole blocking group to manage the intermolecular interaction for high efficiency and narrow emission. The deep blue OLEDs achieve high external quantum efficiency (EQE) of 24.9%, small FWHM of 19nm, and deep blue color coordinate of (0.16, 0.04) with good color stability with increase in doping concentration. To the authors' knowledge, the EQE in this work is one of the highest values reported for the deep blue OLEDs that achieve the BT.2020standard.