Showing papers by "Chihaya Adachi published in 2023"
18 citations
TL;DR: In this paper , a rare example of organic-inorganic 2D perovskite incorporating strong acceptors such as naphthalene diimide (NDI) building blocks between inorganic sheets is presented.
Abstract: 2D organic–inorganic perovskites are an emerging class of materials with great potential for optoelectronics since a wide variety of large functional chromophores can be regularly incorporated. Among this new type of materials, hybrid perovskite systems incorporating strong electron acceptor molecules are considered as a promising approach to designing a new type of functional 2D perovskites for optoelectronics. In this work, a rare example of organic–inorganic 2D perovskite incorporating strong acceptors such as naphthalene diimide (NDI) building blocks between inorganic sheets is presented. This hybrid architecture forms highly air‐stable thin films with a structure consisting of inorganic perovskite monolayers of metal‐halide octahedra separated by bilayers of NDI‐based organic cations. The presence of strong electron‐accepting moieties in this multifunctional donor–acceptor hybrid heterostructure leads to a rare type II heterojunction in which the excitons can be efficiently dissociated via the electron‐transfer process and in which holes and electrons can be easily confined in the inorganic and organic sublayers, respectively. Such an ultimate p–n heterojunction shows improved photoconduction properties with a photocurrent multiplied by ≈40 under white‐light illumination in comparison to a similar 2D perovskite structure containing optically and electrically inert alkyl chains as organic components.
2 citations
TL;DR: In this paper , a facile postmodification by palladium-catalyzed coupling reactions was developed to synthesize a series of donor-acceptor-donor (D-A-D) PPABs.
1 citations
TL;DR: In this paper , a multiple donor-acceptor (D-A) TADF compound with two distinct donor units of 9,10-dihydro-9,9-dimethylacridine (DMAC) and carbazole as the hetero-donor design was developed.
Abstract: A considerable variety of donor-acceptor (D-A) combinations offers the potential for realizing highly efficient thermally activated delayed fluorescence (TADF) materials. Multiple D-A type compounds are one of the promising families of TADF materials in terms of stability as well as efficiencies. However, those emitters are always composed of carbazole-based donors despite a wide choice of moieties used in linearly linked single D-A molecules. Herein, we developed a multiple D-A type TADF compound with two distinct donor units of 9,10-dihydro-9,9-dimethylacridine (DMAC) and carbazole as the hetero-donor design. The new emitter exhibits high photoluminescence quantum yield (PLQY) in various conditions including polar media blend and high concentrations. Organic light-emitting diodes (OLEDs) showed a reasonably high external quantum efficiency (EQE). In addition, we revealed that the multiple-D-A type molecules showed better photostability than the single D-A type molecules, while the operational stability in OLEDs involves dominant other factors.
TL;DR: In this article , the authors present a sudden exciton quenching at the turn-on voltage region in a blue triplet-triplet upconversion (TTU)-based blue fluorescent OLED that limits overall electroluminescence (EL) efficiency.
TL;DR: In this article , the authors investigated why perovskite solar cells degrade in air and found that one of the critical reasons for air-induced PSC degradation is the doping of the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobi-fluorene (spiro-OMeTAD) hole-transport layer with oxygen.
Abstract: After remarkable progress over the past decades, perovskite solar cells (PSCs) currently exhibit efficient solar power conversion efficiency. However, the environmental instability of perovskite materials and devices is still a serious issue, impeding the future commercialization of this technology. Herein, why PSCs degrade in air is investigated and it is found that one of the critical reasons for the air-induced PSC degradation is the doping of the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobi-fluorene (spiro-OMeTAD) hole-transport layer with oxygen. Photoelectron yield spectroscopy reveals that the hole-transport level of the spiro-OMeTAD layer becomes deeper by oxygen doping, increasing an energy barrier for hole extraction. In other words, decreased hole extraction at the perovskite/spiro-OMeTAD interface induces the degradation of PSCs in air. However, this oxygen-induced degradation of PSCs is reversible to some extent by storing PSCs in a vacuum to remove oxygen. In contrast, no detectable degradation of the perovskite light absorber is observed after ≈600 h of air exposure from the results of morphological and structural characterizations. These aspects provide a deeper understanding of PSCs degradation, giving insight into improving long-term durability in air in the future.
TL;DR: In this paper , progress in singlet- and triplet-state utilizations in organic gain media is reviewed to reveal the issues in working with triplets and exciton behaviors that inhibit light oscillations during long excitation pulses are discussed.
Abstract: A continuous-wave (CW) organic solid-state laser is highly desirable for spectroscopy, sensing, and communications, but is a significant challenge in optoelectronics. The accumulation of long-lived triplet excitons and relevant excited-state absorptions, as well as singlet-triplet annihilation, are the main obstacles to CW lasing. Here, progress in singlet- and triplet-state utilizations in organic gain media is reviewed to reveal the issues in working with triplets. Then, exciton behaviors that inhibit light oscillations during long excitation pulses are discussed. Further, recent advances in increasing organic lasing pulse widths from microseconds toward the indication of CW operation are summarized with respect to molecular designs, advanced resonator architectures, triplet scavenging, and potential triplet contribution strategies. Finally, future directions and perspectives are proposed for achieving stable CW organic lasers with significant triplet contribution.
TL;DR: In this article , the defect levels inside the band gap of the NMA-based quasi-2D perovskite are shallow, with a depth of ≈ 0.3 eV, causing a decrease in nonradiative exciton recombination through the defects.
Abstract: Films of the quasi-2D perovskite based on 1-naphthylmethylamine (NMA) are promising as the gain medium for optically pumped lasing and future electrically pumped lasing because of its low lasing threshold and small electroluminescence efficiency rolloff. However, reasons for the low threshold and small efficiency rolloff are still unclear. Therefore, exciton dynamics are investigated in NMA-based quasi-2D perovskite films. It is found that quenching of bright excitons by other excitons or charge carriers is unlikely in NMA-based quasi-2D perovskite films, which is one reason for the low lasing threshold and small efficiency rolloff. Moreover, thermally stimulated current measurements reveal that the defect levels inside the band gap of the NMA-based quasi-2D perovskite are shallow, with a depth of ≈0.3 eV, causing a decrease in nonradiative exciton recombination through the defects. Therefore, population inversion can be easily achieved, leading to the low lasing threshold as well. For fabrication of NMA-based quasi-2D perovskite laser devices with even lower lasing thresholds, a circular-shaped optical resonator, and small-molecule-based defect passivation are used. Optically pumped lasing can be obtained from these devices, with a threshold of ≈1 µJ cm−2, which is one of the lowest values ever reported in any perovskite lasers.
TL;DR: In this article , the relationship between crystal packing motifs and ORTP characteristics in binary cocrystals composed of 1,4-diiodotetrafluorobenzene (DITFB) and a variety of polyaromatic hydrocarbons (PAHs) or their derivatives was investigated.
Abstract: Recently, there has been intense interest in pure organic room-temperature phosphorescence (ORTP) from cocrystals composed of 1,4-diiodotetrafluorobenzene (DITFB) and a variety of polyaromatic hydrocarbons (PAHs) or their derivatives. To expand the possibility of halogen bonding-based cocrystals, we investigate the relationship between the crystal packing motifs and ORTP characteristics in binary cocrystals composed of DITFB and PAHs of phenanthrene (Phen), chrysene (Chry), and pyrene (Pyr), respectively. The σ-hole···π and π-hole···π interactions determine not only the crystal packing motifs but also photoluminescence quantum yields (PLQYs). The Phen-DITFB and Chry-DITFB binary cocrystals with σ-hole···π interactions show higher PLQY compared with that of the Pyr-DITFB binary cocrystal with π-hole···π interaction. Further, to clarify the effect of crystal structures on PLQY, ternary cocrystals are prepared by partially doping Pyr into Phen-DITFB. The backbone of the crystal packing motif of the ternary cocrystal originates from a Phen-DITFB cocrystal with σ-hole···π interaction, and some of the Phen sites are randomly replaced with Pyr molecules. The ORTP emission is derived from Pyr. The maximum PLQY is more than 20% due to suppressing nonradiative decay by changing the crystal packing motif. This article is protected by copyright. All rights reserved.
01 Jan 2023-Journal of Materials Chemistry C. Materials for Optical, Magnetic and Electronic Devices
TL;DR: In this article , two amine/carbonyl-based multi-resonance thermally activated delayed fluorescence (TADF) emitters have been designed and synthesized.
Abstract: Two novel -extended amine/carbonyl-based multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have been designed and synthesized. The two emitters are isomeric, comprised of nine fused rings and show green-yellow emission....
TL;DR: Based on the classic 1,1′:4′,1″−terphenyl fluorophore, a novel near-ultraviolet (NUV) fluorescent BB4Ph (4,4″′−bis(2,3,4,5−tetraphenylphenylphen•1]-yl) is designed, synthesized, and characterized as mentioned in this paper .
Abstract: Based on the classic 1,1′:4′,1″‐terphenyl fluorophore, a novel near‐ultraviolet (NUV) fluorescent BB4Ph (4,4″′‐bis(2,3,4,5‐tetraphenylphen‐1‐yl)(1,1′:4′,1″‐terphenyl) is designed, synthesized, and characterized. BB4Ph exhibits a NUV fluorescence with a λmax of 373 and 380 nm in solution and as a thin film, respectively. The grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals BB4Ph having a high value of order parameter (SGIWAXS) of 0.59 for a molecular layer array normal to the substrate; the angle‐dependent photoluminescence (ADPL) measurement shows Θ (horizontal–dipole ratios) as high as 95% with the neat film. The non‐doped BB4Ph organic light‐emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with 1931 Commission Internationale de l’ Eclairage coordinates (CIEx,y) of (0.16, 0.04), a NUV electroluminescence. With 4P‐Cz (9,9′‐(1,1′:4′,1″:4″,1′″‐quaterphenyl‐4,4′″‐diyl)dicarbazole) as a dopant emitter, doped BB4Ph OLEDs show the highest EQE of 6.99% and a NUV 1931 CIEx,y (0.16, 0.04). The photoluminescence quantum yield is measured for the thin film of BB4Ph and 4P‐Cz:BB4Ph as 68% and 96%, respectively. Hence, the low limits of light outcoupling efficiency (ηout) of the two individual OLEDs are estimated as 31% and 29%, respectively.
TL;DR: In this article , three new 1,2,4,5-tetraphenylimidazole derivatives bearing different electron donors at the N1 position of the imidazoles were synthesized and characterised.
Abstract: Three new 1,2,4,5-tetraphenylimidazole derivatives, 9,9-dimethyl-10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-9,10-dihydroacridine (DMAC-TPI), 10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-10H-phenoxazine (PXZ-TPI), and 10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-10H-phenothiazine (PTZ-TPI), bearing different electron donors at the N1 position of the imidazole were synthesised and characterised. DMAC-TPI and PXZ-TPI showed narrow emission at λPL of 388 and 418 nm in toluene, and in doped films in Zeonex polymer (1 wt.%) at λPL 381 and 407 nm, respectively, with a full width at half maximum (FWHM) ranging 0.42-0.44 eV. DMAC-TPI and PXZ-TPI are predicted to show very low oscillator strength for the low-energy transitions, which aligns to the observed low photoluminescence quantum yields. Both molecules showed a singlet-triplet energy gap (ΔEST of around 1.2 eV) that is much too large to enable reverse intersystem crossing and thermally activated delayed fluorescence. Connecting a donor group to TPI at the N1 position can lead to room temperature phosphorescence (RTP), as the example of PTZ-TPI showed.
TL;DR: In this article , the authors used a clathrate crystal with TADF and H2O molecules to evaluate the effect of hydrogen bonding while maintaining molecular conformations and other intermolecular interactions.
Abstract: Reverse intersystem crossing (RISC) in purely organic molecules has become an attractive research topic since the demonstration of high efficiencies in organic light-emitting diodes using thermally activated delayed fluorescence (TADF). Although the intermolecular interactions have a significant impact on the exciton dynamics, it is generally difficult to identify the quantitative relationship associated with a specific factor. In this work, we used a clathrate crystal with TADF and H2O molecules to evaluate the effect of hydrogen bonding while maintaining molecular conformations and other intermolecular interactions. The hydrogen bonding shifted the charge transfer excited states to lower energies, resulting in superior TADF properties. Although the increase in the RISC rate is considered to enhance the stabilities of TADF molecules, photostability analysis revealed nearly the same degradation speed despite the 3 times faster RISC rate.
TL;DR: In this paper , a proof of concept for realizing the maximum TTU contribution yield in blue OLEDs, achieved through the doping of thermally activated delayed fluorescence (TADF) molecules in the carrier recombination zone.
Abstract: In the process of triplet-triplet upconversion (TTU), a bright excited singlet can be generated because of the collision of two dark excited triplets. In particular, the efficiency of TTU is crucial for achieving a high exciton production yield in blue fluorescence organic light-emitting diodes (OLEDs) beyond the theoretical limit. While the theoretical upper limit of TTU contribution yield is expected to be 60%, blue OLEDs with the maximum TTU contribution are still scarce. Herein, we present a proof of concept for realizing the maximum TTU contribution yield in blue OLEDs, achieved through the doping of thermally activated delayed fluorescence (TADF) molecules in the carrier recombination zone. The bipolar carrier transport ability of TADF materials enables direct carrier recombination on the molecules, resulting in the expansion of the recombination zone. Although the external electroluminescence quantum efficiency of OLEDs is slightly lower than that of conventional TTU-OLEDs due to the low photoluminescence quantum yield of the doped layer, the TTU efficiency approaches the upper limit. Furthermore, the operational device lifetime of OLEDs employing TADF molecules increased by five times compared to the conventional ones, highlighting the expansion of the recombination zone as a crucial factor for enhancing overall OLED performance in TTU-OLEDs.
TL;DR: In this paper , a triazine-based host molecules and Eu(hfa)3(TPPO)2 (hfa: hexafluoroacetylacetonato and TPPO: triphenylphosphine oxide) were used to enhance photoluminescence intensity.
Abstract: Trivalent lanthanide complexes are attractive light emitters owing to their ideal high color purity. Sensitization using ligands with high absorption efficiency is a powerful approach to enhancing photoluminescence intensity. However, the development of antenna ligands that can be used for sensitization is limited due to difficulties in controlling the coordination structures of lanthanides. When compared to conventional luminescent Eu(iii) complexes, a system composed of triazine-based host molecules and Eu(hfa)3(TPPO)2 (hfa: hexafluoroacetylacetonato and TPPO: triphenylphosphine oxide) significantly increased total photoluminescence intensity. Energy transfer from the host molecules to the Eu(iii) ion occurs via triplet states over several molecules, according to time-resolved spectroscopic studies, with nearly 100% efficiency. Our discovery paves the way for efficient light harvesting of Eu(iii) complexes with simple fabrication using a solution process.
14 Mar 2023
TL;DR: In this article , instead of shortening the delayed lifetime of MREs by molecular design, a low-triplet pyrene unit was introduced into an MRE scaffold to achieve narrowband emission and quick removal of triplets simultaneously.
Abstract: Multi-Resonance Emitters (MREs) are a promising candidate for fulfilling the harsh requirements of display applications due to their unique photophysical properties. Recently, MREs have been widely used as a Terminal Emitter (TE) in Hyper Fluorescence Organic Light-Emitting Diodes (HF-OLEDs); however, since MREs are always TADF-active, possessing long triplet lifetimes in milli-second order, they result in severe chemical degradation. The device lifetime of blue OLED is still a challenge. Here, instead of shortening the delayed lifetime of MREs by molecular design, we introduced a low-triplet pyrene unit into an MRE scaffold to achieve narrowband emission and quick removal of triplets in MREs simultaneously. Blue HF-OLED based on the non-TADF MRE demonstrated a high external quantum efficiency (EQE) of 20% and a ten-fold improvement in stability, compared to those of the HF-OLEDs with standard MREs.
TL;DR: In this article , high-quality spin-coated quasi-2D perovskite gain films were prepared using an antisolvent to reduce roughness, and the highly reflective top DBR mirrors were deposited via room-temperature e-beam evaporation.
Abstract: Continuous-wave (CW) lasing in quasi-two-dimensional (2D) perovskite-based distributed feedback cavities has been achieved at room temperature; however, CW microcavity lasers comprising distributed Bragg reflectors (DBRs) have rarely been prepared using solution-processed quasi-2D perovskite films because the roughness of perovskite films significantly increases intersurface scattering loss in the microcavity. Herein, high-quality spin-coated quasi-2D perovskite gain films were prepared using an antisolvent to reduce roughness. The highly reflective top DBR mirrors were deposited via room-temperature e-beam evaporation to protect the perovskite gain layer. Lasing emission of the prepared quasi-2D perovskite microcavity lasers under CW optical pumping was clearly observed at room temperature, featuring a low threshold of ∼1.4 W cm-2 and beam divergence of ∼3.5°. It was concluded that these lasers originated from weakly coupled excitons. These results elucidate the importance of controlling the roughness of quasi-2D films to achieve CW lasing, thus facilitating the design of electrically pumped perovskite microcavity lasers.
TL;DR: In this article , a new hole transport layer (HTL) material was developed for emerging lead halide hybrid perovskite solar cells (PSCs), which provided better hole extraction in PSCs than chemically doped spiro-OMeTAD due to higher electrical conductivity and a more suitable hole transport energy level.
Abstract: N,N-di(4-methoxyphenyl)amino-9,9′-spirobifluorene (spiro-OMeTAD) is a widely used hole transport layer (HTL) material for emerging lead halide hybrid perovskite solar cells (PSCs). Finding alternative HTL materials is required for the future development of more efficient and stable PSCs. Here, we developed a new HTL material of N2,N2,N,7N7-tetrakis(4-methoxyphenyl)benzo[b]benzo[4,5]thieno[2,3-d]thiophene-2,7-diamine (TBTD). Chemically doped TBTD provided better hole extraction in PSCs than chemically doped spiro-OMeTAD due to higher electrical conductivity and a more suitable hole transport energy level. Thus, PSCs with the TBTD HTL showed higher power conversion efficiency (∼21%) than spiro-OMeTAD HTL (∼19%). The operational stability of TBTD-based PSCs was similar to that of spiro-OMeTAD-based PSCs. The findings discussed in this study will aid in the future development of high-performance PSCs.