Thermal Management Enables Stable Perovskite Nanocrystal Light-Emitting Diodes with Novel Hole Transport Material.

The severely insufficient operational lifetime of perovskite light-emitting diodes (LEDs) is incompatible with the rapidly increasing external quantum efficiency, even as it approaches the theoretical limit, thereby significantly impeding the commercialization of perovskite LEDs. In addition, Joule heating induces ion migration and surface defects, degrades the photoluminescence quantum yield and other optoelectronic properties of perovskite films, and induces the crystallization of charge transport layers with low glass transition temperatures, resulting in LED degradation under continuous operation. Here, a novel thermally crosslinked hole transport material, poly(FCA60 -co-BFCA20 -co-VFCA20 ) (poly-FBV), with temperature-dependent hole mobility is designed, which is advantageous for balancing the charge injection of the LEDs and limiting the generation of Joule heating. The optimised CsPbI3 perovskite nanocrystal LEDs with poly-FBV realise approximately a 2-fold external quantum efficiency increase over the LED with commercial hole transport layer poly(4-butyl-phenyl-diphenyl-amine) (poly-TPD), owing to the balanced carrier injection and suppressed exciton quenching. Moreover, because of the Joule heating control provided by the novel crosslinked hole transport material, the LED utilising crosslinked poly-FBV has a 150-fold longer operating lifetime (490 min) than that utilizing poly-TPD (3.3 min). The study opens a new avenue for the use of PNC LEDs in commercial semiconductor optoelectronic devices.

Dinuclear Pt(II) Complexes with Red and NIR Emission Governed by Ligand Control of the Intramolecular Pt-Pt Distance.

Red and near-infrared (NIR) phosphorescent double-decker dinuclear Pt(II) complexes were synthesized, and their structural and spectroscopic properties were characterized. The Pt(II) complexes, which are composed of achiral ligands and are themselves chiral, were shown to exist as racemic mixtures using single-crystal X-ray crystallography. The Pt(II) complexes have different intramolecular Pt-Pt distances that are governed by the electronic characteristics of the component C^N ligands. Specifically, strengthening of π-back-donation between Pt(II) and N atom of the C^N ligand leads to shortening of the Pt-Pt distance. The results of both experimental and computational investigations show that the Pt-Pt distances in the dinuclear Pt(II) complexes significantly influence the band gap energies and corresponding emission wavelengths. Consequently, the uncovered C^N ligand based method to finely control intramolecular Pt-Pt distances in dinuclear Pt(II) complexes can be utilized as a guideline for the design of the double-decker dinuclear Pt(II) complexes with red and NIR tuned phosphorescence.

Synthesis and Characterization of Self-Polishing Polyurethane Copolymers.

Synthesizing copolymers from Zn acrylate monomers is an effective strategy employed in the self-polishing materials industry. In this study, we designed and synthesized polyurethane-based self-polishing copolymers with improved surface adhesion properties. The synthesized polyurethane copolymers were characterized using Fourier transform infrared spectroscopy and inductively coupled plasma optical emission spectrometry. The properties of Zn-based polyurethane copolymers were compared with those of Zn-free polyurethane as reference. The erosion rates of the Zn-based polyurethane SPC films were determined by measuring changes in the film thickness after dynamic immersion tests. In comparison to Zn-free polyurethane, the Zn-based polyurethane self-polishing copolymers demonstrated effective self-polishing and surface adhesion properties.

Synthesis and Characterization of Diketopyrrolopyrrole-Based Conjugated Polymers with Bithiophene and Biselenophene for Organic Thin Film Transistors.

In this study, two new thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPP)-based polymers, poly{2,5-bis(2-dodecylhexadecyl)-3,6-bis(thieno[3,2-b]thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2, 2'-bithiophene} (PTTDPP-BT) and {2,5-bis(2-dodecylhexadecyl)-3,6-bis(thieno[3,2-b]thiophen-2-yl) pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2'-selenophene} (PTTDPP-BSe), which contained bithiophene (BT) and biselenophene (BSe) units, respectively, were designed and synthesized. The introduction of BT and BSe units affected the optical, electrochemical, morphological, and charge transport properties of the polymers. Experimental results revealed that the frontier molecular orbital energy levels of PTTDPP-BT were slightly higher because of the relatively strong electron donating ability of the sulfur atom and the polymer also exhibited good solubility. The maximum mobility in the case of PTTDPP-BT at 250 °C was 0.068 cm² V-1 s-1 and that of PTTDPP-BSe was 0.029 cm² V-1 s-1 (at 200 °C).

Synthesis of Novel Polyacrylates Containing Cyclotetrasiloxane for Fouling-Release Coating Applications.

An acrylate monomer containing cyclotetrasiloxane (CTS) were designed and synthesized for anti-fouling coating applications. New acryl-based copolymers consisting of styrene and CTS, poly(styrene-co-CTS)s, were synthesized by changing molar ratios via free radical polymerization. The properties of poly(styrene-co-CTS)s were compared with those of poly(styrene) (PS) as a reference. The content of CTS in the copolymer increased its hydrophobicity also decreased whereas its surface decreased. Protein adsorption studies were conducted to evaluate their fouling-release properties.

Thermally Cross-Linkable Styrene-Based Host Materials for Solution-Processed Organic Light-Emitting Diodes.

Thermally cross-linkable host materials, DV-TPACZ, DV-TPADBCZ, and TV-TPBI, were designed and synthesized for solution-processed organic light-emitting diodes (OLEDs). The synthesized styrene-functionalized host materials were thermally cross-linked by curing at 150-200 °C without using a polymerization initiator. Excellent solvent resistance was observed for all cured host films. They exhibited low highest occupied molecular orbital energy levels of 5.4-5.7 eV, which indicated a low hole injection barrier from the hole transport layer to the emissive layer. A solution-processed red phosphorescent OLED with 5 wt% (MPHMQ)2Ir (tmd) dopant in the thermally cross-linkable DV-TPACZ host exhibited a current efficiency of 5.3 cd/A, power efficiency of 3.2 lm/W, and external quantum efficiency of 3.6%.

Synthesis and Characterization of Novel Triarylmethane-Based Dyes for Thermally Stable Blue Color Filters.

Two new triarylmethane-based dye molecules with a dimeric structure, TAM-1 and TAM-2, were designed and synthesized as potential blue color filter materials for liquid-crystal displays. The dimeric structure of TAM-1 was designed to improve the thermal stability of a well-known blue dye, Victoria Blue BO. TAM-2 was designed to further improve the solubility of TAM-1 by introducing long alkyl ester groups. The synthesized dyes TAM-1 and TAM-2 were transmissive in the wavelength range of 410-460 nm and showed good thermal stability with 5% weight degradation temperatures (T5d) of 259 °C and 289 °C, respectively, and less than 1% of weight loss at 230 °C. Moreover, TAM-2 showed excellent solubility (20.1 wt%) as opposed to Victoria Blue BO (0.03 wt%) and TAM-1 (3.5 wt%) in PGMEA.

Synthesis and Properties of Fluorinated Styrene Copolymers as Antibiofouling Coatings.

A series of polystyrene (PS) copolymers containing 2,3,4,5,6-pentafluorostyrene units with different monomer ratios were prepared for antifouling applications. PS, poly(styrene-co-pentafluorostyrene) (poly(S-co-FS)), and poly(pentafluorostyrene) (PFS) were synthesized by free-radical polymerization and characterized by 1H NMR, Fourier-transform infrared spectroscopy, and gel permeation chromatography. The surface energy of the polymer films decreased with increasing content of fluorinated styrene. Protein adsorption experiments were carried out on the synthesized polymer films using fluorescein isothiocyanate-labeled bovine serum albumin as a fluorescent protein. The photo-luminescence intensity of the protein-adsorbed polymer films decreased dramatically as the content of hydrophobic fluorinated styrene increased, suggesting that poly(S-co-FS) copolymers and PFS could be used as potential antibiofouling coatings.

Blue Phosphorescent Bipyridine-Based Iridium(III) Complex for Vacuum-Deposited Organic Light-Emitting Diodes.

We have synthesized and characterized a blue phosphorescent iridium(III) complex (dfpypy)2Ir(tftamp), which contains 2',6'-difluoro-2,3'-bipyridine (dfpypy) as the main ligand and 4-methyl-2-(3'-trifluoromethyl-1'H-1',2',4'-triazol-5'-yl)pyridine (tftamp) as the ancillary ligand. The photophysical, electrochemical, and electroluminescent (EL) properties of (dfpypy)2Ir(tftamp) were investigated. Vacuum-deposited blue and white organic light-emitting diodes (OLEDs) were fabricated using (dfpypy)2Ir(tftamp) in 1,3-bis(carbazol-9-yl)benzene (mCP) as the emitting layer. The EL spectrum of (dfpypy)2Ir(tftamp) exhibited emission maximum at 472 nm with a full-width at half-maximum (FWHM) of 81 nm and Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.27) at 100 cd · m-2. In addition, white-light-emitting devices were fabricated, which exhibited CIE coordinates of (0.42, 0.40) and a correlated color temperature (CCT) of 3,237 K at 1000 cd · m-2, close to the standard warm-white light CIE coordinates of (0.44, 0.40) and CCT of 3,000 K.

Synthesis of a Zr-Based Metal-Organic Framework with Spirobifluorenetetrabenzoic Acid for the Effective Removal of Nerve Agent Simulants.

A new microporous Zr(IV)-based metal-organic framework (MOF) containing 4,4',4″,4‴-(9,9'-spirobi[fluorene]-2,2',7,7'-tetrayl)tetrabenzoic acid (Spirof-MOF) was synthesized, characterized, and size-controlled for the adsorption and decomposition of a nerve agent simulant, dimethyl 4-nitrophenylphosphate (DMNP). Spirof-MOF showed a hydrolysis half-life (t1/2) of 7.5 min to DMNP, which was confirmed by using in situ 31P NMR spectroscopy. Additionally, size-controlled Spirof-MOFb (∼1 µm) exhibited a half-life of 1.8 min and 99% removal within 18 min for DMNP. The results show that Spirof-MOF is a new active material in removing nerve agent simulants by adsorption and hydrolytic decomposition.

Anti-Biofouling Effect of PEG-Grafted Block Copolymer Synthesized by RAFT Polymerization.

Poly(glycidyl methadrylate-block-styrene) (PGMA-b-PS), a block copolymer consisting of glycidyl methacrylate and styrene, was synthesized via reversible addition-fragmentation chain transfer living polymerization. The synthesized PGMA-b-PS was then grafted with low-molecular-weight polyethylene glycol (PEG) via epoxy ring opening to give PGMA-g-PEG-b-PS, which was evaluated as an anti-biofouling coating material. As a preliminary test for the anti-biofouling effect, a protein adsorption experiment was performed on the synthesized block copolymer surface. The block copolymers were spin-coated onto silicon wafers, and protein adsorption experiments were carried out using fluorescein isothiocyanate conjugate-labeled bovine serum albumin. The fluorescence intensity of the protein adsorbed on the block copolymer surface was compared with that of a polystyrene film as a reference. The synthesized PGMA-g-PEG-b-PS film showed much lower fluorescence intensity than that of the PS film.

(E)-2,2'dibromo-7,7'-bis(diphenylamino)-9,9' bifluorenylidene as a new electron acceptor for organic photovoltaic cells.

(E)-2,2'-Dibromo-7,7'-bis(diphenylamino)-9,9'-bifluorenylidene (BDPABF) was synthesized as a new non-fullerene-type electron acceptor for organic photovoltaic cells. The UV-visible absorption spectra of BDPABF showed two main bands at 319 and 474 nm in a chloroform solution and 320 and 481 nm as a solid thin film. The optical band gap of BDPABF was determined to be 2.34 eV by measuring the onset absorption wavelength of the solid thin film. The ionization potential of BDPABF was determined to be 5.59 eV using photoelectron spectroscopy. The measured lowest unoccupied molecular orbital energy level of BDPABF was - 3.25 eV. Its electron-accepting ability was investigated through a Stern-Volmer quenching experiment. The intensity of the photoluminescence of P3HT dramatically decreased upon the addition of BDPABF. The measured Stern-Volmer quenching constant was 5.3 x 10(4) M(-1). Photovoltaic devices were fabricated using P3HT as the electron donor and BDPABF as the electron acceptor at various composition ratios. The optimized device showed a maximum power conversion efficiency of 0.27% with an open-circuit voltage of 0.71 V, short-circuit current density of 1.29 mA/cm2, and fill factor of 0.29 after thermal annealing at 100 degrees C for 5 min.

Synthesis and characterization of organic semiconducting polymers containing dithienylfluorenone for use in organic photovoltaic cells.

2,7-Bis(5-bromo-4-hexylthiophen-2-yl)-9H-fluoren-9-one (DTFO) was synthesized as a new electron-accepting material in semiconducting polymers for use in photovoltaic devices. The synthesized DTFO was polymerized with two different electron-donating counter monomers: 2,7-dibromo-9,9-dioctyl-9H-fluorene (DOF) and 2,6-bis(trimethyltin)-4,8-di(2-ethylhexyloxyl)benzo [1,2-b:4,5-b']dithiophene (BDT). Two alternating copolymers, poly(DTFO-alt-DOF) and poly(DTFO-alt-BDT), were synthesized through the Suzuki and Stille coupling polymerizations, respectively. The synthesized polymers exhibited good solubility in common solvents and show good thermal stability up to 350 °C. The optical band gap energies of poly(DTFO-alt-DOF) and poly(DTFO-alt-BDT) were determined to be 2.44 and 2.23 eV, respectively. The positions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the polymers were determined by cyclic voltammetry (CV). One of these devices showed a power conversion efficiency of 0.50%, with an open-circuit voltage of 0.67 V, a short-circuit current of 2.34 mA/cm2, and a fill factor of 0.30 under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW/cm2).

Fullerene derivatives as electron acceptors for organic photovoltaic cells.

Energy is currently one of the most important problems humankind faces. Depletion of traditional energy sources such as coal and oil results in the need to develop new ways to create, transport, and store electricity. In this regard, the sun, which can be considered as a giant nuclear fusion reactor, represents the most powerful source of energy available in our solar system. For photovoltaic cells to gain widespread acceptance as a source of clean and renewable energy, the cost per watt of solar energy must be decreased. Organic photovoltaic cells, developed in the past two decades, have potential as alternatives to traditional inorganic semiconductor photovoltaic cells, which suffer from high environmental pollution and energy consumption during production. Organic photovoltaic cells are composed of a blended film of a conjugated-polymer donor and a soluble fullerene-derivative acceptor sandwiched between a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-coated indium tin oxide positive electrode and a low-work-function metal negative electrode. Considerable research efforts aim at designing and synthesizing novel fullerene derivatives as electron acceptors with up-raised lowest unoccupied molecular orbital energy, better light-harvesting properties, higher electron mobility, and better miscibility with the polymer donor for improving the power conversion efficiency of the organic photovoltaic cells. In this paper, we systematically review novel fullerene acceptors synthesized through chemical modification for enhancing the photovoltaic performance by increasing open-circuit voltage, short-circuit current, and fill factor, which determine the performance of organic photovoltaic cells.

Synthesis and properties of new low band gap semiconducting polymers.

Low band gap organic semiconducting polymers were prepared as p-type donors for organic photovoltaic devices. A novel dibrominated monomer composed of phenothiazine, thiophene, and benzothiadiazole (DPDTBT) was synthesized as a low band gap core block. DPDTBT was copolymerized with three different boronic esters of dithiophene, fluorene, and phenothiazine by the Suzuki coupling polycondensation reaction. The band gap energies of the synthesized polymers ranged between 2.05 and 2.11 eV, depending on the polymer structure. Bulk heterojunction solar cells fabricated using the polymers and [6,6]-phenyl C71-butyric acid methyl ester (PC70BM) as an acceptor were characterized. The best power conversion efficiency obtained from the fabricated devices under simulated AM 1.5 G solar irradiation of 100 mW/cm2 was 0.46%.

Synthesis and characterization of novel soluble fulleropyrrolidine derivatives and their photovoltaic performance.

Currently, [60] fullerene derivatives are the focus of considerable research due to their important roles in many fields, especially material science. In this study, we synthesized the following two novel fulleropyrrolidine derivatives: C60-fused N-methyl-(4-hexyloxybenzen-2-yl) pyrrolidine, (p-HOPF) and C60-fused N-methyl-(2-hexyloxybenzen-2-yl) pyrrolidine, (o-HOPF). Structural assignments of the two fullerene derivatives were made through 1H NMR and FAB-MS. We also measured the optical and electrochemical properties of p-HOPF and o-HOPF through UV/Vis spectrophotometry and cyclic voltammetry. We found that the difference in the position of the alkoxyl substituent on the phenyl ring greatly affects the characteristics of the molecules. In particular, from the 1H NMR spectrum, we found that the hydrogen atoms on the carbons adjacent to the oxygens in p-HOPF and o-HOPF have completely different chemical environments. In order to study the effects of the substituent group positions on photovoltaic performance, photovoltaic devices were fabricated. The highest power conversion efficiency, 0.71%, was achieved when using o-HOPF as the electron acceptor.

Pure red phosphorescent organic light-emitting diodes made of iridium(III) complex with thiophene-quinoline ligand.

A cyclometalated iridium(II) complex, bis(2-thiophen-2-yl-quinolinato)(acetoacetonate)iridium(II) [(tq)2Ir(III)(acac)] was synthesized for use in phosphorescent organic light-emitting diodes. The photophysical and electrochemical properties of the iridium(Ill) complex were characterized by UV-visible absorption, photoluminescence, and cyclic voltammetry. The maximum UV-visible absorption of (tq)2Ir(acac) was observed at 289 nm. (Tq)2Ir(acac) in dichloromethane showed its maximum photoluminescence (PL) emission at 629 nm. The optical band gap energy of (tq)2Ir(III)(acac) was measured to be 2.11 eV, and the HOMO energy level of (tq)2Ir(Ill)(acac) was calculated to be -5.08 eV. The T1 state of (tq)2Ir(lll)(acac), calculated from the PL emission maximum (2.01 eV), was well matched with the T1 level of CBP (2.6 eV). The phosphorescent organic light-emitting diode with a configuration of ITO/PEDOT:PSS/alpha-NPD/TCTA/CBP:(tq)2Ir(II)(acac)(8 wt%)/BCP/Alq3/LiF/Al was fabricated and characterized. Light emission from the device was observed at a low turn-on voltage of 4.3 V. The device showed a maximum brightness of 24,000 cd/m2 at 16.3 V and an external quantum efficiency of 11.1% with a Commission Internationale de l'Eclairage (CIE) coordinate of (0.690, 0.310).

Indolocarbazole-Based Photo-Crosslinkable Hole-Transporting Layer for Efficient Solution-Processed Organic Light-Emitting Diodes.

We designed and synthesized a new indolocarbazole-based polymer, poly(N,N-diphenyl(5,11-dihexylindolo[3,2,1-jk]carbazol-2-yl)amine) (PICA), for solution-processed organic light-emitting diodes (OLEDs). The highest occupied and lowest unoccupied molecular orbital energy levels of this polymer, -5.25 and -2.46 eV, respectively, are suitable for hole transport from the anode to the emissive layer. PICA was photo-crosslinked by UV irradiation with ethane-1,2-diyl bis(4-azido-2,3,5,6-tetrafluorobenzoate) (FPA) as the photoinitiator. Successful crosslinking was confirmed by a decreased intensity in the azide-stretching FT-IR peak and solvent test with toluene (a suitable solvent for PICA). The PICA film photo-crosslinked with 3 wt% FPA showed enhanced solvent resistance (90%) compared to the non-crosslinked neat PICA film (<20%). Moreover, OLED devices using PICA-based hole-transporting layers exhibited better device performance (EQE/LE/PE: 8.88%/12.97/8.12 in red devices, 10.84%/38.47 cd/A/25.06 lm/W in green devices) than those using poly-TPD:FPA. We demonstrated that the photo-crosslinked PICA can be applied as a hole-transporting layer in solution-processed OLEDs.

Corroboration of the Toms effect from a frictional drag reducing self-polishing copolymer.

A novel frictional drag reducing self-polishing copolymer (FDR-SPC) was first developed by the authors. The FDR-SPC is a special derivative of an SPC that was designed to achieve skin frictional drag reduction in turbulent water flow by releasing polyethylene glycol (PEG) into water through a hydrolysis reaction. Thus, the FDR-SPC coating acts as a continuous medium accommodating countless, molecular-level polymer injectors. However, direct evidence of such PEG release has not yet been demonstrated. Here, we report the results of in situ PEG concentration measurement based on the planar laser-induced fluorescence (PLIF) method. Polyethylene glycol methacrylate (PEGMA) was probed by the fluorescent functional material dansyl, and the fluorescence intensity from dansyl-PEG was then measured to quantify the concentration in the flow. The near-wall concentration of dansyl-PEG is observed to range from 1 to 2 ppm depending on the flow speed, which corroborates the existence of a drag reducing function for the FDR-SPC. In the concurrent measurement of skin friction, the present FDR-SPC specimen exhibited a skin friction reduction ratio of 9.49% at the freestream flow speed [Formula: see text]. In the comparative experiment of dansyl-PEGMA solution injection, the skin friction was found to decrease by 11.9%, which is in reasonable accordance with that for the FDR-SPC.

Non-Fullerene Acceptors with Benzodithiophene-Based Fused Planar Ring Cores for Organic Solar Cells.

Fused aromatic rings are widely employed in organic solar cell (OSC) materials due to their planarity and rigidity. Here, we designed and synthesized four two-dimensional non-fullerene acceptors, D6-4F, D6-4Cl, DTT-4F, and DTT-4Cl, based on two new fused planar ring structures of f-DTBDT-C6 and f-DTTBDT. Owing to the desirable phase separation formed in the blend films and the higher energy levels induced by the extra alkyl groups, PM6:D6-4F-based devices achieved a high VOC = 0.91 V with PCE = 11.10%, FF = 68.54%, and JSC = 17.75 mA/cm2. Because of the longer π-conjugation of the f-DTTBDT core with nine fused rings, DTT-4F and DTT-4Cl showed high molar extinction coefficients and broad absorption bands that enhanced the current density of OSCs. Finally, the PM6:DTT-4F-based devices achieved a JSC = 19.82 mA/cm2 with PCE = 9.68%, VOC = 0.83 V, and FF = 58.85%.