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Meer BB, Sharma D, Tak S, Bisen GG, Shirsat MD, Girija KG, Ghosh SS. Effect of thermal annealing on an emissive layer containing a blend of a small molecule and polymer as host for application in OLEDs. RSC Adv 2023; 13:33668-33674. [PMID: 38020036 PMCID: PMC10652355 DOI: 10.1039/d3ra06271f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Accepted: 11/04/2023] [Indexed: 12/01/2023] Open
Abstract
In order to improve the performance of OLEDs, a host-guest mixture was used as an emissive layer. To have better host properties, a mixture of different materials with suitable properties can also be used as a host. In this study, we used a mixture of a polymer and a small molecule as the host and studied the effect of thermal annealing on the emissive layer properties by using Ir(ppy)3 as the emitter. UV-visible absorption, steady-state and time-resolved photoluminescence, scanning electron microscopy, atomic force microscopy, and optical microscopic studies were performed to study the film properties. Devices were fabricated and their current-voltage and luminance-voltage characteristics were studied. Charge-carrier mobility in the devices was studied by dark CELIV and transient electroluminescence methods. We show that, below the glass transition temperature of the polymer, the small molecules formed aggregates due to thermal annealing, which was beneficial for the device performance in the lower-temperature range, mainly due to the improved electron mobility. However, this aggregate formation was detrimental in the higher-temperature range, as it led to inefficient energy transfer due to the increased pure phase formation. At temperatures above the glass transition temperature of the polymer, the small molecules were seen to be distributed more uniformly into the polymer matrix. However, as a result of the degradation of the polymer property due to degradation of the primary chain of the phenyl ring of the polymer, this uniform distribution was not of any use and the device performance deteriorated.
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Affiliation(s)
- Bushra Basharatali Meer
- Optoelectronics Laboratory, Department of Physics, Kavayitri Bahinabai Chaudhari North Maharashtra University Jalgaon-425001 Maharashtra India
| | - Dhruv Sharma
- Optoelectronics Laboratory, Department of Physics, Kavayitri Bahinabai Chaudhari North Maharashtra University Jalgaon-425001 Maharashtra India
| | - Swapnil Tak
- Optoelectronics Laboratory, Department of Physics, Kavayitri Bahinabai Chaudhari North Maharashtra University Jalgaon-425001 Maharashtra India
| | - Gauri Govardhan Bisen
- Optoelectronics Laboratory, Department of Physics, Kavayitri Bahinabai Chaudhari North Maharashtra University Jalgaon-425001 Maharashtra India
| | - Mahendra D Shirsat
- RUSA Centre for Advanced Sensor Technology, Department of Physics, Babasaheb Ambedkar Marathwada University Aurangabad-431004 Maharashtra India
| | | | - Sanjay Sanatan Ghosh
- Optoelectronics Laboratory, Department of Physics, Kavayitri Bahinabai Chaudhari North Maharashtra University Jalgaon-425001 Maharashtra India
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Soldano C, Laouadi O, Gallegos-Rosas K. TCTA:Ir(ppy) 3 Green Emissive Blends in Organic Light-Emitting Transistors (OLETs). ACS OMEGA 2022; 7:43719-43728. [PMID: 36506198 PMCID: PMC9730476 DOI: 10.1021/acsomega.2c04718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Accepted: 11/07/2022] [Indexed: 06/17/2023]
Abstract
Organic light-emitting transistors are photonic devices combining the function of an electrical switch with the capability of generating light under appropriate bias conditions. Achieving high-performance light-emitting transistors requires high-mobility organic semiconductors, optimized device structures, and highly efficient emissive layers. In this work, we studied the optoelectronic response of green blends (TCTA:Ir(ppy)3) with varying doping concentrations in the limit of field-effect within a transistor device configuration. Increasing the dye concentration within the blend leads to a quenching of the photoluminescence signal; however, when implemented in a multilayer stack in a transistor, we observed an approximately 5-fold improvement in the light output for a 10% Ir(ppy)3 doping blend. We analyzed our results in terms of balanced charge transport in the emissive layer, which, in the limit of field-effect (horizontal component), leads to an improved exciton formation and decay process. While the performances of our devices are yet to achieve the state-of-the-art diode counterpart, this work demonstrates that engineering the emissive layer is a promising approach to enhance the light emission in field-effect devices. This opens the way for a broader exploitation of organic light-emitting transistors as alternative photonic devices in several fields, ranging from display technology to flexible and wearable electronics.
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Sanderson S, Vamvounis G, Mark AE, Burn PL, White RD, Philippa BW. Understanding the performance differences between solution and vacuum deposited OLEDs: A computational approach. J Chem Phys 2022; 156:214703. [DOI: 10.1063/5.0091142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Solution-processing of organic light-emitting diode films has potential advantages in terms of cost and scalability over vacuum-deposition for large area applications. However, solution processed small molecule films can have lower overall device performance. Here, novel molecular dynamics techniques are developed to enable faster simulation of solvent evaporation that occurs during solution processing and give films of thicknesses relevant to real devices. All-atom molecular dynamics simulations are then used in combination with kinetic Monte Carlo transport modeling to examine how differences in morphology stemming from solution or vacuum film deposition affect charge transport and exciton dynamics in films consisting of light-emitting bis(2-phenylpyridine)(acetylacetonate)iridium(III) [Ir(ppy)2(acac)] guest molecules in a 4,4′-bis( N-carbazolyl)biphenyl host. While the structures of the films deposited from vacuum and solution were found to differ, critically, only minor variations in the transport properties were predicted by the simulations even if trapped solvent was present.
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Affiliation(s)
- Stephen Sanderson
- College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
| | - George Vamvounis
- College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
| | - Alan E. Mark
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Paul L. Burn
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
- Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Ronald D. White
- College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
| | - Bronson W. Philippa
- College of Science and Engineering, James Cook University, Cairns, QLD 4878, Australia
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Wang V, Javey A. A Resonantly Driven, Electroluminescent Metal Oxide Semiconductor Capacitor with High Power Efficiency. ACS NANO 2021; 15:15210-15217. [PMID: 34436863 DOI: 10.1021/acsnano.1c05729] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Electroluminescence can be generated from a wide variety of emissive materials using a simple, generic device structure. In such a device, emissive materials are deposited by various means on a metal oxide semiconductor capacitor structure across which alternating current voltage is applied. However, these devices suffer from low external efficiencies and require the application of high voltages, thus hindering their practical usage and raising questions about the possible efficiencies that can be achieved using alternating current driving schemes in which injection of bipolar charges does not occur simultaneously. We show that appropriately chosen reactive electrical components can be leveraged to generate passive voltage gain across the device, allowing operation at input voltages below 1 V for devices across a range of gate oxide thicknesses. Furthermore, high power efficiencies are observed when using thermally activated delayed fluorescence emitters deposited by a single thermal evaporation step, suggesting that the efficiency of a light-emitting device with simplified structure can be high.
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Affiliation(s)
- Vivian Wang
- Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California 94720, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Ali Javey
- Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California 94720, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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Electronic and transport properties of the dual-emitter organometallic compound IrQ(ppy)2. J Organomet Chem 2021. [DOI: 10.1016/j.jorganchem.2021.121814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Sanderson S, Vamvounis G, Mark AE, Burn PL, White RD, Philippa BW. Unraveling exciton processes in Ir(ppy) 3:CBP OLED films upon photoexcitation. J Chem Phys 2021; 154:164101. [PMID: 33940818 DOI: 10.1063/5.0044177] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Emissive layers in phosphorescent organic light-emitting diodes commonly make use of guest-host blends such as Ir(ppy)3:CBP to achieve high external quantum efficiencies. However, while the Ir(ppy)3:CBP blend has been studied experimentally, crucial questions remain regarding how exciton diffusion is dependent on the distribution of the guest in the host, which can currently only be addressed at the atomic level via computational modeling. In this work, kinetic Monte Carlo simulations are utilized to gain insight into exciton diffusion in Ir(ppy)3:CBP blend films. The effects of both guest concentration and exciton density on various system properties are analyzed, including the probability of singlet excitons being converted to triplets, and the probability of those triplets decaying radiatively. Significantly, these simulations suggest that triplet diffusion occurs almost exclusively via guest-guest Dexter transfer and that concentration quenching of triplets induced by guest-guest intermolecular dipole-dipole interactions has a negligible effect at high exciton densities due to the prevalence of triplet-triplet annihilation. Furthermore, results for vacuum deposited morphologies derived from molecular dynamics simulations are compared to the results obtained using a simple cubic lattice approximation with randomly distributed guest molecules. We show that while differences in host-based processes such as singlet diffusion are observed, overall, the results on the fate of the excitons are in good agreement for the two morphology types, particularly for guest-based processes at low guest concentrations where guest clustering is limited.
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Affiliation(s)
- Stephen Sanderson
- College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
| | - George Vamvounis
- College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
| | - Alan E Mark
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Paul L Burn
- Centre for Organic Photonics & Electronics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Ronald D White
- College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
| | - Bronson W Philippa
- College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
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Li P, Lu ZH. Interface Engineering in Organic Electronics: Energy‐Level Alignment and Charge Transport. SMALL SCIENCE 2020. [DOI: 10.1002/smsc.202000015] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Affiliation(s)
- Peicheng Li
- Department of Materials Science and Engineering University of Toronto Toronto M5S 3E4 Canada
| | - Zheng-Hong Lu
- Department of Materials Science and Engineering University of Toronto Toronto M5S 3E4 Canada
- Department of Physics Center for Optoelectronics Engineering Research Yunnan University Kunming 650091 P. R. China
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Bangsund JS, Van Sambeek JR, Concannon NM, Holmes RJ. Sub-turn-on exciton quenching due to molecular orientation and polarization in organic light-emitting devices. SCIENCE ADVANCES 2020; 6:eabb2659. [PMID: 32821834 PMCID: PMC7413727 DOI: 10.1126/sciadv.abb2659] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 06/25/2020] [Indexed: 05/20/2023]
Abstract
The efficiency of organic light-emitting devices (OLEDs) is often limited by roll-off, where efficiency decreases with increasing bias. In most OLEDs, roll-off primarily occurs due to exciton quenching, which is commonly assumed to be active only above device turn-on. Below turn-on, exciton and charge carrier densities are often presumed to be too small to cause quenching. Using lock-in detection of photoluminescence, we find that this assumption is not generally valid; luminescence can be quenched by >20% at biases below turn-on. We show that this low-bias quenching is due to hole accumulation induced by intrinsic polarization of the electron transport layer (ETL). Further, we demonstrate that selection of nonpolar ETLs or heating during deposition minimizes these losses, leading to efficiency enhancements of >15%. These results reveal design rules to optimize efficiency, clarify how ultrastable glasses improve OLED performance, and demonstrate the importance of quantifying exciton quenching at low bias.
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