Solution-processed Devices Research Articles

Long-Wavelength Light-Emitting Electrochemical Cells: Materials and Device Engineering.

Long-wavelength light-emitting electrochemical cells (LECs) are potential deep-red and near infrared light sources with solution-processable simple device architecture, low-voltage operation, and compatibility with inert metal electrodes. Many scientific efforts have been made to material design and device engineering of the long-wavelength LECs over the past two decades. The materials designed the for long-wavelength LECs cover ionic transition metal complexes, small molecules, conjugated polymers, and perovskites. On the other hand, device engineering techniques, including spectral modification by adjusting microcavity effect, light outcoupling enhancement, energy down-conversion from color conversion layers, and adjusting intermolecular interactions, are also helpful in improving the device performance of long-wavelength LECs. In this review, recent advances in the long-wavelength LECs are reviewed from the viewpoints of materials and device engineering. Finally, discussions on conclusion and outlook indicate possible directions for future developments of the long-wavelength LECs. This review would like to pave the way for the researchers to design materials and device engineering techniques for the long-wavelength LECs in the applications of displays, bio-imaging, telecommunication, and night-vision displays.

Solvent-Vapor-Assisted Self-Assembly of Semiconducting Polymers at the Air–Liquid Interface: Impact on Nanoscale Morphology and Optoelectrical Anisotropy

Rapid evaporation of volatile solvents sometimes forcefully limits the time of molecular self-organization toward the growth of highly oriented semicrystalline thin films of organic semiconducting polymers (OSPs). We are reporting a unified approach harnessing the key advantages of the “floating-film transfer method” (FTM) along with the effect of solvent-vapor-assisted controlled evaporation of the solvents to fabricate a high-quality active semiconducting layer for better-performing organic field-effect transistors. To accomplish this, regioregular poly(3-hexylthiophene-2,5-diyl) has been used as a model OSP, and the fabricated films were thoroughly characterized using several tools to understand the structure–property correlation by exploring the fundamental properties. Oriented thin films thus fabricated exhibited highly “edge-on” oriented molecular packing with reduced interlamellar spacing, dh00, and extended π-conjugation length and lower exciton bandwidth. Moreover, quantum-dot-like aggregated nanostructuring within the crystalline domains, as evidenced by high-resolution transmission electron microscopy, forms a network of interconnected conductive pathways. This leads to enhanced field-effect mobility along the polymer backbone, μ|| = 0.0498 cm2 V–1 s–1, which is around five times higher than that of the thin films prepared by conventional FTM. Thus, our study demonstrated a facile route to obtain uniaxially oriented and highly crystalline OSP films suitable for solution-processed high-performance organic electronic device applications.

Ion transfer into solution-processed electrodes can significantly shift the p–n junction and emission efficiency of light-emitting electrochemical cells

A light-emitting electrochemical cell (LEC) comprises mobile ions in its active material, which enable for in situ formation of a p–n junction by electrochemical doping. The position of this emissive p–n junction in the interelectrode gap is important, because it determines whether the emission is affected by constructive or destructive interference. An appealing LEC feature is that the entire device can be fabricated by low-cost solution-based printing and coating. Here, we show, somewhat unexpectedly, that the replacement of conventional vacuum-deposited indium-tin-oxide (ITO) for the positive anode with solution-processed poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) can result in an increase in the peak light-emission output by 75%. We demonstrate that this emission increase is due to that the p–n junction shifts from a position of destructive interference in the center of the interelectrode gap with ITO to a position of constructive interference closer to the anode with PEDOT:PSS. We rationalize the anodic p–n junction shift by significant anion transfer into the soft and porous PEDOT:PSS electrode during LEC operation, which is prohibited for the ITO electrode because of its compact and hard nature. Our study, thus, contributes with important design criteria for the attainment of efficient light emission from solution-processed LEC devices.

Molecular-Switch-Embedded Solution-Processed Semiconductors.

Recent improvements in the performance of solution-processed semiconductor materials and optoelectronic devices have shifted research interest to the diversification/advancement of their functionality. Embedding a molecular switch capable of transition between two or more metastable isomers by light stimuli is one of the most straightforward and widely accepted methods to potentially realize the multifunctionality of optoelectronic devices. A molecular switch embedded in a semiconductor can effectively control various parameters such as trap-level, dielectric constant, electrical resistance, charge mobility, and charge polarity, which can be utilized in photoprogrammable devices including transistors, memory, and diodes. This review classifies the mechanism of each optoelectronic transition driven by molecular switches regardless of the type of semiconductor material or molecular switch or device. In addition, the basic characteristics of molecular switches and the persisting technical/scientific issues corresponding to each mechanism are discussed to help researchers. Finally, interesting yet infrequently reported applications of molecular switches and their mechanisms are also described.

Photo- and electro-luminescence properties of phenothiazine/phenoxazine-functionalized pyrene-fused pyrazaacenes with aggregation-induced emission

Two pyrene-fused pyrazaacenes containing phenothiazine and phenoxazine units, 10-(phenanthro[4,5-abc]phenazin-11-yl)-10H-phenothiazine (Py-PTZ) and 10-(phenanthro[4,5-abc]phenazin-11-yl)-10H-phenoxazine (Py-PXZ), were successfully synthesized and their thermal, optical and electronic properties were investigated systematically. Both of them are nearly non-emissive in chloroform solution but become highly emissive in the mixed solution of chloroform and n-hexane and in the solid states. The solution-processed doped devices with a structure of ITO/PEDOT:PSS (30 nm)/CBP:Py-PTZ or Py-PXZ (x wt%) (25 nm)/TPBi (35 nm)/Liq (2 nm)/Al (150 nm) were fabricated, in which the Py-PTZ-based doped device exhibited a maximum luminance (Lmax) of 2570 cd/m2, a maximum current efficiency (CEmax) of 2.67 cd/A and a maximum external quantum efficiency (EQEmax) of 1.64%, and the Py-PXZ-based doped device showed Lmax, CEmax and EQEmax of 4554 cd/m2, 6.39 cd/A and 3.81%, respectively.

Organic-Inorganic Hybrid Device with a Novel Deep-Blue Emitter of a Donor-Acceptor Type, with ZnO Nanoparticles for Solution-Processed OLEDs.

Two new deep-blue emitters with bipolar properties based on an organoboron acceptor and carbazole donor were newly synthesized: 2-(9H-carbazol-9-yl)-5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho [3,2,1-de]anthracen-7-yl)-5H-benzo[b]carbazole (TDBA-BCZ) and 5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho [3,2,1-de]anthracen-7-yl)-8-phenyl-5,8-dihydroindolo[2,3-c]carbazole (TDBA-PCZ). The two emitters showed deep-blue and real-blue photoluminescence emission in their solution and film states, respectively. The doped spin-coated films were prepared using synthesized materials and showed a root-mean-square roughness of less than 0.52 nm, indicating excellent surface morphology. The doped devices, fabricated via a solution process using TDBA-BCZ and TDBA-PCZ as the dopants, showed electroluminescence peaks at 428 and 461 nm, corresponding to the Commission Internationale de L'éclairage (CIE) coordinates of (0.161, 0.046) and (0.151, 0.155), respectively. The external quantum efficiency (EQE)/current efficiency (CE) of the solution-processed forward devices, with TDBA-BCZ and TDBA-PCZ as dopants, were 7.73%/8.67 cd/A and 10.58%/14.24 cd/A, respectively. An inverted OLED device fabricated using rod-shaped ZnO nanoparticles as an electron injection layer showed a CE of 1.09 cd/A and an EQE of 0.30%.

Synthesis and characterization of thermally cross-linkable poly(iminoarylene)-based hole injection layer for solution-processed organic light-emitting diodes

A cross-linkable poly(iminoarylene), poly[(9,9-dioctyl-N-(p-tolyl)-9H-fluoren-2-amine)–co-(9,9-bis(4-(bicyclo[4.2.0]octa-1(6),2,4-trien-7-yloxy)phenyl)-N-(p-tolyl)-9H-fluoren-2-amine)] [poly(FA-co-BFA)], was synthesized as a hole injection layer (HIL) for solution-processed organic light-emitting diodes (OLEDs). Poly(FA90-co-BFA10) containing 10 mol% of benzocyclobutene (BCB) which is a thermally curable functional group was used in this study. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of poly(FA90-co-BFA10) were measured to be −5.14 and −2.31 eV, respectively. After heating at 150 °C for 40 min, the spin-cast poly(FA90-co-BFA10) film became completely crosslinked without requiring the use of additional initiators. The crosslinked thin film showed good film-forming properties and excellent solvent resistance (up to 99 %). A photo-crosslinked poly[bis(4-butypheny)-bis(phenyl)benzidine] (poly-TPD) was used as the hole-transporting layer (HTL) on top of the crosslinked poly(FA90-co-BFA10). Finally, a solution-processed red phosphorescent OLED device with the structure of indium tin oxide/poly(FA90-co-BFA10)/poly-TPD/emissive layer/TPBi/LiF/Al was fabricated and characterized. The device showed a low turn-on voltage (Von) of 3.5 V, a reasonably high current efficiency (CE) of 16.6 cd/A, and an external quantum efficiency (EQE) of 12.5 %, which are better than those of the corresponding reference device using PEDOT:PSS as the HIL. Moreover, the device fabricated using the poly(FA90-co-BFA10) HIL demonstrated a longer lifetime than that fabricated using PEDOT:PSS.

Narrowband Emissive TADF Conjugated Polymers towards Highly Efficient Solution-Processible OLEDs.

Thermally activated delayed fluorescence (TADF) conjugated polymers usually show broad emission spectra due to the large structure relaxation, which is not desirable for high-quality organic light-emitting diode (OLED) displays. Herein, through attaching multiple resonance (MR) induced emitting moiety as pendant onto the polycarbazole backbone, TADF conjugated polymers with narrowband emission are demonstrated. The obtained conjugated polymers exhibit typical TADF characteristics with narrowband emission with full-width at half-maximums (FWHMs) of 33-43 nm. The solution-processed devices employing these polymers as emissive layers realize excellent performances with maximum external quantum efficiency (EQE) of 17.5 %, emission peak at 496 nm and FWHM of 34 nm.

All Solution-Processed Inorganic, Multilevel Memristors Utilizing Liquid Metals Electrodes Suitable for Analog Computing.

Herein, we report a solution-processable memristive device based on bismuth vanadate (BiVO4) and titanium dioxide (TiO2) with gallium-based eutectic gallium-indium (EGaIn) and gallium-indium-tin alloy (GaInSn) liquid metal as the top electrode. Scanning electron microscopy (SEM) shows the formation of a nonporous structure of BiVO4 and TiO2 for efficient resistive switching. Additionally, the gallium-based liquid metal (GLM)-contacted memristors exhibit stable memristor behavior over a wide temperature range from -10 to +90 °C. Gallium atoms in the liquid metal play an important role in the conductive filament formation as well as the device's operation stability as elucidated by I-V characteristics. The synaptic behavior of the GLM-memristors was characterized, with excellent long-term potentiation (LTP) and long-term depression (LTD) linearity. Using the performance of our device in a multilayer perceptron (MLP) network, a ∼90% accuracy in the handwriting recognition of modified national institute of standards and technology database (MNIST) was achieved. Our findings pave a path for solution-processed/GLM-based memristors which can be used in neuromorphic applications on flexible substrates in a harsh environment.

Synchronous enhancement of responsivity, response time and, spectral range in solution processed CdS photodetector upon modification with PEDOT:PSS

Solution processed photodetectors with high responsivities and simple fabrication schemes are high on demand for variety of emerging opto-electronic applications. However, these devices suffer from sluggish response and recovery times. In this work, we demonstrate the simultaneous enhancement of the responsivity, response time and spectral range of detection in a solution-processed device based on organic/inorganic hybrid junction. A solution-processed flexible CdS photodetector is fabricated using a facile and economical chemical bath deposition technique. The fabricated pristine-CdS device exhibits responsivity and response time of 50 mA/W and 5.4 s. The resultant device exhibits enhanced responsivity and response time of around 740 mA/W and 0.6 s, respectively, upon modification with the PEDOT:PSS conducting polymer. These values of PEDOT-modified device are one order larger than pristine-CdS detector. Further, PEDOT:PSS modification also extends the responsivity of the device from UV-Vis to NIR spectra. NIR responsivity in the hybrid device, is imputed to the photothermal property of the PEDOT:PSS layer. Thus, the overall device spectral response is accredited to the simultaneous existence of photoelectric and photo-thermal phenomena. The observed responsivity and faster response time is ascribed primarily to the built-in potential at interface of CdS-PEDOT:PSS, which not only facilitates efficient separation of photo carriers but also leads to a reduction in the recombination of excitons. Given the simple approach and excellent enhancement in the device performance, the idea demonstrated here could be useful to design high performance opto-electronic device based on solution-processed techniques.

Efficient generation of emissive many-body correlations in copper-doped colloidal quantum wells

Colloidal quantum wells (CQWs) provide an appealing platform to achieve emissive many-body correlations for novel optoelectronic devices, given that they act as hosts for strong carrier Coulomb interactions and present suppressed Auger recombination. However, the demonstrated high-order excitonic emission in CQWs requires ultrafast pumping with high excitation levels and can only be spectrally resolved at the single-particle level under cryogenic conditions. Here, through systematic investigation using static power-dependent emission spectroscopy and transient carrier dynamics, we show that Cu-doped CdSe CQWs exhibit continuous-wave-pumped high-order excitonic emission at room temperature with a large binding energy of ∼64 meV. We attribute this unique behavior to dopant excitons in which the ultralong lifetime and the highly localized wavefunction facilitate the formation of many-body correlations. The spectrally resolved high-order excitonic emission generated at power levels compatible with solar irradiation and electrical injection might pave the way for novel solution-processed solid-state devices. • Continuous-wave-pumped high-order excitonic emission at room temperature is shown • The excitation level is compatible with solar irradiation and electrical injection • 64 meV binding energy enables spectrally resolved high-order excitonic emission Yu et al. demonstrate continuous-wave-pumped high-order excitonic emission at room temperature in Cu-doped CdSe colloidal quantum wells. The properties of dopant excitons enable an ultra-low excitation level compatible with solar irradiation or electrical injection and a binding energy of ∼64 meV, which makes the high-order excitonic emission spectrally resolvable at room temperature.

Over 16% Efficient Solution-Processed Cu(In,Ga)Se2 Solar Cells via Incorporation of Copper-Rich Precursor Film.

Solution processing of Cu(In,Ga)Se2 (CIGS) absorber is a highly promising strategy for a cost-effective CIGS photovoltaic device. However, the device performance of solution-processed CIGS solar cells is still hindered by the severe non-radiative recombination resulting from deep defects and poor crystal quality. Here, a simple and effective precursor film engineering strategy is reported, where Cu-rich (CGI >1) CIGS layer is incorporated into the bottom of the CIGS precursor film. It has been discovered that the incorporation of the Cu-rich CIGS layer greatly improves the absorber crystallinity and reduces the trap state density. Accordingly, more efficient charge generation and charge transfer are realized. As a result of systematic processing optimization, the champion solution-processed CIGS device delivers an improved open-circuit voltage of 656mV, current density of 33.15mAcm-2 , and fill factor of 73.78%, leading to the high efficiency of 16.05%.

Use of a Multiple Hydride Donor To Achieve an n-Doped Polymer with High Solvent Resistance.

The ability to insolubilize doped semiconducting polymer layers can help enable the fabrication of efficient multilayer solution-processed electronic and optoelectronic devices. Here, we present a promising approach to simultaneously n-dope and largely insolubilize conjugated polymer films using tetrakis[{4-(1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)phenoxy}methyl]methane (tetrakis-O-DMBI-H), which consists of four 2,3-dihydro-1H-benzoimidazole (DMBI-H) n-dopant moieties covalently linked to one another. Doping a thiophene-fused benzodifurandione-based oligo(p-phenylenevinylene)-co-thiophene polymer (TBDOPV-T) with tetrakis-O-DMBI-H results in a highly n-doped film with bulk conductivity of 15 S cm-1. Optical absorption spectra provide evidence for film retention of ∼93% after immersion in o-dichlorobenzene for 5 min. The optical absorption signature of the charge carriers in the n-doped polymer decreases only slightly more than that of the neutral polymer under these conditions, indicating that the exposure to solvent also results in negligible dedoping of the film. Moreover, thermal treatment studies on a tetrakis-O-DMBI-H-doped TBDOPV-T film in contact with another undoped polymer film indicate immobilization of the molecular dopant in TBDOPV-T. This is attributed to the multiple electrostatic interactions between each dopant tetracation and up to four nearby anionic doped polymer segments.

Tetradentate Pt(II) Complexes with Peripheral Hindrances for Highly Efficient Solution-Processed Blue Phosphorescent OLEDs.

Two tetradentate Pt(II) complexes with peripheral bulky-group hindrances [Pt(pzpyOczpy-B1) and Pt(pzpyOczpy-B2)] were synthesized and fully investigated for their structural and blue phosphorescent properties. Both X-ray crystallography and computational simulation revealed that bulky substituents incorporated into the C-pyrazolyl and C-pyridinyl positions lie out of the cyclometallated plane, thus alleviating the intramolecular distortions as well as reducing the intermolecular interaction in the solid state. In dichloromethane, their emission peaks at 460 nm with a narrow full width at half-maximum (FWHM) of less than 50 nm, and the photoluminescent quantum yields are over 95% with short decay lifetimes (<5 μs). Solution-processed blue devices are fabricated based on the two complexes. Device A based on Pt(pzpyOczpy-B1) shows excellent electroluminescent performances with the maximum current efficiency, power efficiency, and external quantum efficiency of 47.0 cd/A, 24.6 lm/W, and 22.9%, respectively. The understanding on inert peripheral hindrances provides an effective approach to designing Pt(II) complexes for high-quality blue phosphorescent emitters.

Delayed Fluorescence by Triplet-Triplet Annihilation from Columnar Liquid Crystal Films.

Delayed fluorescence (DF) by triplet–triplet annihilation (TTA) is observed in solutions of a benzoperylene-imidoester mesogen that shows a hexagonal columnar mesophase at room temperature in the neat state. A similar benzoperylene-imide with a slightly smaller HOMO–LUMO gap, that also is hexagonal columnar liquid crystalline at room temperature, does not show DF in solution, and mixtures of the two mesogens show no DF in solution either, because of collisional quenching of the excited triplet states on the imidoester by the imide. In contrast, DF by TTA from the imide but not from the imidoester is observed in condensed films of such mixtures, even though neat films of either single material are not displaying DF. In contrast to the DF from the monomeric imidoester in solution, DF of the imide occurs from dimeric aggregates in the blend films, assisted by the imidoester. Thus, the close contact of intimately stacked molecules of the two different species in the columnar mesophase leads to a unique mesophase-assisted aggregate DF. This constitutes the first observation of DF by TTA from the columnar liquid crystalline state. If the imide is dispersed in films of polybromostyrene, which provides an external heavy-atom effect facilitating triplet formation, DF is also observed. Organic light-emitting diodes (OLEDs) devices incorporating these liquid crystal molecules demonstrated high external quantum efficiency (EQE). On the basis of the literature and to the best of our knowledge, the EQE reported is the highest among nondoped solution-processed OLED devices using a columnar liquid crystal molecule as the emitting layer.

Synthesis and Luminescent Properties of 1,4,5-Triphenylimidazole‒Phenothiazine Fluorophores.

Two blue donor-acceptor fluorophores with 1,4,5-triphenylimidazole as the electron-transporting unit and phenothiazine as the hole-transporting unit were synthesized by grafting 1,4,5-triphenylimidazole moieties onto 3- and 3,7-position of the phenothiazine core and characterized by spectroscopic methods. Their thermal stability, photophysical, electrochemical and electroluminescence properties were systematically investigated. These compounds exhibit good thermal stability and show blue emission in dichloromethane solution and thin solid films. The solution-processed doped devices were fabricated by using these fluorophores as the emitting dopant in 1,3-bis(N-carbazolyl)benzene host, in which the device fabricated from the fluorophore containing two 1,4,5-triphenylimidazole moieties exhibited blue emission with a luminance of 648cd/m2 and external quantum efficiency of 1.48%.

Enhancing quantum efficiency in Pt-based emitters using a pendant closo-monocarborane cluster to enforce charge neutrality

The use of organometallic triplet emitters in OLED applications may be complicated when the luminescent complex bears a formal charge. By designing ligands containing pendant closo-monocarborane clusters [CB11H11]−, it is possible to neutralize the otherwise cationic cores of cyclometalated Pt(II) complexes bearing bis-carbenes, resulting in significantly enhanced photophysical properties. Herein, we report four Pt(II) complexes decorated with a monoanionic closo-monocarborane by coupling the cluster to the classic cyclometallating moiety, phenylpyridine (ppy). All four complexes were fully characterized by NMR, HR-MS, UV–Vis, and cyclic voltammetry. Complexes 1b, 1c and 2a were characterized by single-crystal X-ray diffraction. Moreover, all four complexes show interesting photophysical behaviors, with complex 1a exhibiting a photoluminescent quantum yield of 97% in a 2 wt% PMMA film. This high efficiency prompted the incorporation of 1a and 1c into an OLED device using solution processing, resulting in green emission with CIE coordinates of (0.28, 0.55) for 1a and yellow emission with CIE coordinates of (0.44, 0.50) for 1c. The measured maximum external quantum efficiency (EQEmax) was 18.51% for 1a, an EQEmax that is among the highest for solution-processed OLED devices containing Pt(II) complexes with simple cyclometalated ppy ligands.

Direct Optical Patterning of Nanocrystal-Based Thin-Film Transistors and Light-Emitting Diodes through Native Ligand Cleavage

Developing techniques of advanced patterning for colloidal nanocrystals (NCs) is essential to construct high-performance electronic/optoelectronic devices. However, conventional NC patterning methods require complicated photolithography processes and/or delicately designed photocrosslinkers. Here, we develop a direct, photoresist-free method to pattern functional NCs while avoiding any photosensitive molecules. In our approach, the solubility of NCs is switched through cleaving native organic ligands under UV light exposure. Developing with the mother solvent produces fine patterns with feature sizes (as low as 10 μm) comparable to that of conventional photolithography. Importantly, the obtained patterns of NCs allow postpatterning ligand exchange. As representatives, we demonstrate patterned NC-based thin-film transistors (TFTs) and quantum dot light-emitting diodes (QLEDs). The In2O3 NC-based TFTs are turned from inactive to active using the patterning process and display substantially enhanced electronic performances upon ligand exchange with inorganic ligands. Furthermore, exquisite fluorescence quantum dot (QD) patterns are enabled. The QLEDs fabricated with ZnCl2-treated green QD patterns exhibit electroluminescence performances that are comparable to those of unpatterned QLEDs. Our strategy offers a powerful yet simple patterning technique for fabricating low-temperature thin-film electronics and optoelectronics, which is expected to be a versatile and extensible approach for solution-processed NC-based thin-film device manufacturing.

Amine-Terminated Carbon Dots Linking Hole Transport Layer and Vertically Oriented Quasi-2D Perovskites through Hydrogen Bonds Enable Efficient LEDs.

Close attention to the interfaces of solution-processed metal halide perovskite-based light-emitting devices (LEDs) is crucial for their optimal performance. Solution processing of these devices typically leads to the formation of van der Waals interfaces with a weak connection between different functional layers, leaving great room for improvement in charge transport through strengthening of the interlayer interaction. Here, we have realized a hydrogen-bond-assisted interface that makes use of ultrasmall amine-terminated carbon dots to enhance the interaction between the hole transport layer made of PEDOT:PSS and the hybrid lead bromide perovskite emitting layer, which not only promotes the hole injection efficiency but also orients the quasi-2D perovskite crystals penetrating the vertical direction of the device without any, or very few, horizontal grain boundaries, which has a profound effect on the photophysical and transport properties of the emitting layer. As a result, LEDs based on quasi-2D perovskites show up to 24.5% external quantum efficiency, 80 000 cd m-2 brightness, and over 5-fold extended longevity.

Methoxy-substituted carbazole-based polymers obtained by RAFT polymerization for solution-processable organic light-emitting devices

New electroactive vinyl monomers, i.e., 3,6-dimethoxy-9-(4-vinylphenyl)-9H-carbazole and 3,6-dimethoxy-9-(3-vinylphenyl)-9H-carbazole were prepared by palladium catalyzed reactions of dimethoxy-9H-carbazole with 1-bromo-4-vinylbenzene or 1-bromo-3-vinylbenzene, respectively. Living radical polymerization of these monomers was carried out using 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid as a RAFT agent affording polymers with controlled molecular weight (up to Mn = 20,000) and low polydispersity (Đ<1.5). The obtained polymers exhibited delayed fluorescence caused by relaxation of excimer states. The lifetimes of long-lived components up to 2.6 μs were obtained for the excimer emission by multi-exponential fitting of photoluminescence decay curves. The polymers were tested in solution-processed OLEDs. Green thermally-activated-delayed-fluorescence OLEDs with polymers as hole transporting materials demonstrated lower turn-on voltage and enhanced charge balance in emission layer compared to device fabricated using the commercial hole-transporting material. Additionally, the phosphorescent OLEDs based on red phosphor as dopant and the synthesized polymer as a host materials were fabricated and characterized. The best device showed external quantum efficiency of 10.6%.