Small Molecular Materials Research Articles

3PTZ and 3PXZ small molecular hole-transporting materials in polymer light-emitting diodes

The fabricated polymer light-emitting diodes (PLEDs) with new small molecular hole transport layers, 1,3,5-tri(10H-phenothiazin-10-yl) benzene (3PTZ) and 1,3,5-tri(10H-phenoxazin-10-yl) benzene (3PXZ).

One-step synthesis of low-cost perylenediimide-based cathode interfacial materials for efficient inverted perovskite solar cells

Interface engineering plays an important role in improving the performance of perovskite devices. Herein, we reported two perylenediimide small molecular cathode interface materials (CIMs), PDI-2N and PDI-4N, synthesized by a simple method and with good alcohol soluble, which could be used as cathode interfacial layer (CIL) for high-performance inverted perovskite solar cells (PVSCs). The PDI-4N exhibits larger electrical conductivity, electron mobility and self-doping properties than PDI-2N because of more dimethylamino functional groups in the amide positions. Based on these superiorities, a peak PCE of 21.33% with PDI-4N as CIL was achieved, which is the highest PCE for PDI-based interlayer materials as the cathode interlayer in inverted PVSCs. While the PCE with PDI-2N as CIL is only 17.41%. The significant improvement in device efficiency for PDI-4N based device is due to reduced defect density, lower dark current, larger recombination resistance and better surface morphology, which improved charge transport and collection at the PC61BM/Ag interface. Moreover, the ambient stabilities of PVSCs with PDI-2N and PDI-4N as CIL show that the CILs can effectively improve the device stability, and good stability with a PCE loss of only ∼3.0% after 600 h is also obtained. In a word, this work will provide us with molecular design approach by one-step to develop novel cathode interface materials with functional side chains for high-efficiency PVSCs.

Progesterone Phospholipid Gel for Intramuscular Administration Prepared by In Situ-Phase Separation.

Long-term daily injection of progesterone for the treatment of threatened abortion can be a source of considerable pain to patients. To reduce the frequency of injections and improve patient compliance, a novel injectable phospholipid-based phase separation gel (PPSG) was prepared using small molecular materials such as phospholipids, medium-chain triglycerides (MCTs), and ethanol. Progesterone was loaded into PPSGs to promote rapid gel formation in situ via a sol-gel transformation mechanism, thereby achieving a sustained controlled release. Furthermore, progesterone was distributed in the oil-water interface layer and within the oil phase. Solvent exchange drives phase transitions, and phospholipid vesicle formation and rupture are likely to promote drug release and gel degradation. At a drug loading of 140 mg/mL, a progesterone release of up to 60% could be reached within 9 days according to the release curve in vitro. Pharmacokinetic studies demonstrated that the progesterone-loaded PPSGs released the drug continuously for over 7 days, the half-life was eight times higher than that of progesterone oil solution, and relative bioavailability of up to 184.90% was obtained. Collectively, the sustained release properties for hydrophobic cargos would effectively enhance patient compliance. Moreover, PPSGs are promising drug delivery systems that have high market value and biosafety given the readily accessible and safe excipients.

Highly Efficient White Organic Light-Emitting Diodes Based on Phosphorescent Iridium Complexes with Multi-Light-Emitting Layers

White organic light-emitting diodes (WOLEDs) incorporating a blend of blue, green and red phosphorescent small molecular materials are presented in this article. 4,4′,4″-Tris(carbazol-9-yl)triphenylamine (TcTa) and 9-(4-tert-Butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi) with different transmission characteristics were selected as hosts for different emitting layers aim to promote holes transport, which will reinforce carriers’ balance and broaden carrier composite. On account of adaptive energy levels of the utilized dopants and hosts, secured phosphorescent WOLED displayed high efficiencies, low operating voltage and slow efficiency roll-off. In addition, distribution of carriers’ recombination zone and spectral of change were studied in detail to further understand the light-emitting mechanisms of obtained WOLEDs. Finally, by majorizing the dosage concentration of (fbi)2Ir(acac) (bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N,C3)iridium(acetylacetonate)) and the architectures of WOLEDs, the optimal device exhibited the maximum efficiencies of 44.92 cd A−1, 42.85 lm W−1, 16.8%, respectively, turn on voltage of 2.6 V and Commission International de l’Eclairage coordinates of (0.337, 0.458) at the brightness level of 3000 cd m−2.

Low-cost planar organic small molecules as hole transport materials for high efficient perovskite solar cells

Planar organic small molecular hole transport materials (HTMs) have been vigorously developed and utilized in perovskite solar cells (PSCs) with impressive power conversion efficiencies (PCE). However, the price of common HTMs, for instance Spiro-OMeTAD is expensive due to its tedious synthesis and low product yields, it remains challenging to develop high-performance and low-cost organic small molecular HTMs. In this work, a series of molecule, as planar HTMs were constructed by combined carbazole core with planar donor phenothiazine or phenoxazine as backbone, and 1,2-diethoxyethane or n-hexane as side chains, ca. TEG-CZ-PTZ, TEG-CZ-POZ, He-CZ-PTZ and He-CZ-POZ. The results showed that phenoxazine-based TEG-CZ-POZ and He-CZ-POZ have better hole transport efficiency than the phenothiazine-based TEG-CZ-PTZ and He-CZ-PTZ. Meanwhile, TEG-CZ-PTZ and TEG-CZ-POZ with 1,2-diethoxyethane as side chains on carbazole core performed better in hole transporting process than He-CZ-PTZ and He-CZ-POZ with n-hexane. Thus, the PSC based on TEG-CZ-POZ has achieved a best PCE of 21.03%, outperforming the PSCs based on Spiro-OMeTAD (20.74%). More importantly, the estimated cost for lab-synthesis of TEG-CZ-POZ is much lower than that of Spiro-OMeTAD (46.3 $/g vs 92 $/g), suggesting its promising application for efficient and low-cost PSCs.

High Performance and Stable Organic Solar Cells Fabricated by Y-Series Small Molecular Materials as the Interfacial Modified Layer

The organic solar cell (OSC) has received tremendous consideration for the impressive increased power conversion efficiency (PCE) from 11% to over 18% in the last decade, but another main parameter, the stability, still needs further study to meet the requirements of commercialization. Generally, the inverted structure device shows more stability than the conventional one owing to the structure characteristics, but even so, the performance and stability of the OSC device still need further improvement because of some undesirable contact between the electron transport layer (typically transition metal oxide like ZnO) and the active layer. Here, three Y-series small molecular acceptor materials (Y6, BTP-eC9, and L8-BO) are used as an interfacial modified layer (IML), which could optimize the interfacial characterization of the devices and thus enhance both the performance and stability. As a result, the insertion of the IML improved the interlayer charge transport capacity by passivating the surface of ZnO, leading to the enhancement of short circuit current density (JSC), fill factor, and PCE of the OSCs. Furthermore, because of the protection of the IML, the OSCs show outstanding stability compared to the control device (without IML), which could maintain 80% performance of the device over 150 h.

Adjustment of active protons of end-electron-withdrawing groups in small molecules for different memory characteristics

Owing to the diverse design strategy and convenient structural modification, the small molecular organic materials have been widely applicated in the fabrication of memory devices with complex memory behavior. In this work, we successfully synthesized two asymmetric quinacridone derivatives, BQTCH and BQTCE, with the same electron donors and molecular backbone, but different terminal groups. The sandwich-structured memory devices based on BQTCH and BQTCE have also successfully been prepared via spin-coating. The optical properties, packing performances, thermal stabilities and surface morphologies of the small molecules and their corresponding films are characterized via UV–vis and emission spectra, AFM, TGA and XRD. The I–V curves indicate all the as-prepared devices exhibit excellent memory performances, and the sandwich-structured memory devices based on ITO/BQTCH/Al exhibit a ternary memory behavior (WORM type from OFF to ON1 but FLASH type from ON1 to ON2), while the memory devices based on ITO/BQTCE/Al exhibit a typical ternary memory behavior (WORM type). To explain this difference, DFT molecular simulation and the energy level diagrams of HOMO and LUMO orbitals of BQTCH and BQTCE are investigated to demonstrate the crucial role of terminal groups in influencing the memory behavior.

High-performance Self-powered Perovskite Photodetector Based On Cesium Iodide Doped Spiro-OMeTAD Hole Transport Material

Hole transport materials play an essential role in the performance of perovskite detectors (PDs). Therefore, hole transport materials with excellent performance can significantly promote photoinduced holes' extraction rate and mobility. Spiro-OMeTAD, a small organic molecular material, has high solubility and excellent film-forming properties and is ideal for the hole transport layer (HTL) of photodetectors. In this work, a small amount of CsI is introduced into Spiro-OMeTAD together with Li-TFSI and TBP as additives. It is found that CsI and TBP formed a complex, which inhibited the agglomeration of Li-TFSI in Spiro-OMeTAD, thus preventing the rapid evaporation of TBP from leaving some cracks Spiro-OMeTAD. The photodetectors exhibit broadband response from near-ultraviolet to near-infrared (300–800 nm), achieving fast response (rise/fall time is 54.1/10.7 μs) and low dark current density (9.72 ×10−10 A cm−2). The detector can be self-powered at zero bias voltage, the external quantum efficiency (EQE) is 88%, the Responsivity (R) is 0.48 A W−1, and the detectivity (D*) is close to 2.7 × 1013 Jones. When the photovoltaic detector is placed in a nitrogen-filled glove box without special packaging for more than two months, the EQE remains 98.1% of the original. This study provides a simple method for fabricating a large area of high-performance planar PDs.

Oxidized indanthrone as a cost-effective and high-performance organic cathode material for rechargeable lithium batteries

Despite the numerous reports on organic cathode materials for rechargeable batteries, it is a huge challenge to simultaneously satisfy energy density and cycling stability, mainly due to the dissolution in aprotic electrolytes. Herein, we report a novel small molecular organic cathode material (SMOCM), namely oxidized indanthrone (oIDT), synthesized via a simple oxidation of industrially available indanthrone (IDT). Benefiting from the extensive aromatic nucleus and oxidation of unfavorable dihydropyrazine moiety to useful pyrazine, it achieves superior comprehensive electrochemical performance to other SMOCMs for lithium batteries so far reported, including a high energy density (273 mAh g–1 × 2.45 = 668 Wh kg–1) and excellent capactiy retension under high current rate (75% @ 2000 mA g–1) or after long-term cycling (76% @ 1000th cycle). Additionally, the investigation also provides insightful mechanism understandings on the redox reaction and electrode evolution of SMOCMs.

Symmetrically Fluorinated Benzo[1,2-b:4,5-b']dithiophene-Cored Donor for High-Performance All-Small-Molecule Organic Solar Cells with Improved Active Layer Morphology and Crystallinity.

Side-chain engineering is an efficient molecular design strategy for morphology optimization and performance improvement of organic solar cells (OSCs). Herein, a novel small-molecule donor C-2F, which owns a benzo[1,2-b:4,5-b']dithiophene (BDT) central unit with a symmetrically difluorinated benzene ring as a conjugated side chain, has been synthesized. The conjugated side chain possesses both the symmetry and halogenation effect in novel small molecular donor material. The photovoltaic devices were fabricated with N3 as an acceptor. C-2F:N3 based devices achieved an outstanding power conversion efficiency of 14.64% with a Jsc of 24.87 mA/cm2, a Voc of 0.85 V, and an FF of 69.33%. Then, we investigated the basic material properties, photovoltaic mechanism, and active layer morphology, and the results show that this molecular design strategy of the symmetrically difluorinated moiety as the conjugated side chain provides an effective method for fine-tuning the molecular stacking pattern and active layer phase separation morphology, to improve the all-small-molecule (ASM) OSCs' performances.

Recent Advances and Prospects of Small Molecular Organic Thermoelectric Materials.

Thermoelectric (TE) materials possess unique energy conversion capabilities between heat and electrical energy. Small organic semiconductors have aroused widespread attention for the fabrication of TE devices due to their advantages of low toxicity, large area, light weight, and easy fabrication. However, the low TE properties hinder their large-scale commercial application. Herein, the basic knowledge about TE materials, including parameters affecting the TE performance and the remaining challenges of the organic thermoelectric (OTE) materials, are initially summarized in detail. Second, the optimization strategies of power factor, including the selection and design of dopants and structural modification of the dope-host are introduced. Third, some achievements of p- and n-type small molecular OTE materials are highlighted to briefly provide their future developing trend; finally, insights on the future development of OTE materials are also provided in this study.

Enhancing the performance of perovskite solar cells through simple bilateral active site molecule assisted surface defect passivation

Surface defects of perovskite film seriously restrict the photovoltaic performance of perovskite solar cells (PSCs). Therefore, it’s extremely important to develop effective surface defect passivation methods to further enhance the performance of PSCs. In this work, we design and synthesize a small molecular material (4-cyanophenyl) methanamine iodide (CMAI) by incorporating bilateral functional sites of nitrile (–CN) and ammonium (–NH3+) groups. The research manifests that CMAI can not only passivate the lead defects, but also fill the iodide ion vacancy, resulting in the significant reduction of trap state density, the effective suppression of nonradiative recombination, as well as the preferable carrier transport from the perovskite to the hole transport layer. By optimizing the treatment conditions, the CMAI-treated device exhibits an impressive efficiency of 21.59% together with excellent humidity stability, thoroughly over-performing the control device. This work provides a simple and efficient passivation strategy for fabrication of highly stable and efficient PSCs.

Designing phenyl-di-p-tolyl-amine-based asymmetric small molecular donor materials with favorable photovoltaic parameters

In the quest to enhance photovoltaic devices' efficiency and swift progress in the organic solar cell, community scientists are focusing on small molecules donors. The four specific donor molecules, namely TDMDN1, TDMDN2, TDMDN3, and TDMDN4, are designed from recently reported synthetic TDMDN reference molecules. The designed molecules TDMDN1-TDMDN4 have phenyl-di-p-tolyl-amine attached with different acceptors (terminal side). Quantum chemical and photovoltaic parameters of TDMDN1-TDMDN4 were estimated through DFT at MPW1PW91/6–31 G+ (d,p) . The parameters that affect the photophysical properties, exciton dynamics, chemical reactivity, and charge mobility of TDMDN1-TDMDN4 were described by calculating absorption profile, transition density matrix, frontier molecular orbit, and density of state, respectively. The result of all analyses demonstrates that TDMDN1-TDMDN4 proved more competent in executing the parameters mentioned above than TDMDN. Among all designed donors, TDMDN4 is recognized as an appropriate material for photovoltaic application due to its encouraging parameters involving reduced HOMO-LUMO energy gap (1.79 eV), lowest transition energy (1.50 eV), and highest λmax value with chloroform (826 nm). The binding energy of TDMDN4 (0.29 eV) has a low value compared to the TDMDN (0.35 eV). In addition, a complex of TDMDN4 with PC61BM further verifies suitable combination. All designed donor molecules are highly recommended to attain suitable photophysical properties in solar cells and thus are proposed for the elite performance of small molecular solar cell devices.

Insights into the Impact of Nanostructural Properties on Powder Tribocharging: The Case of Milled Salbutamol Sulfate.

The impact of the crystallinity of organic solid materials on their tribocharging propensity is well reported. However, no unequivocal explanation about the potential underlying mechanism(s) could be found so far in the literature. This study reports the effect that different degrees of crystalline disorder has on the tribocharging propensity of a small molecular organic material, salbutamol sulfate (SS). Ball-milling was used to induce structural transformations in the crystalline structure of SS. Particles with different nanostructures were produced and analyzed for their solid-state, particle properties, and tribocharging. It was found that differences in the amorphous content among the processed particles and related moisture levels had an impact on powder tribocharging. A correlation between the latter and the nanostructural properties of the particles was also established. The presence of interfaces between nanodomains of different densities and shorter average lengths within the phases seems to lead to a mitigation of charge. This suggests that undetected, subtle nanostructural differences of materials can affect powder handling and processability by altering their tribocharging. The present findings demonstrate the nanostructural implications of powder triboelectrification, which can help toward the rational design of a wide variety of organic solids.

Design of dopant-free small molecular hole transport materials for perovskite solar cells: a viewpoint from defect passivation

The recent advances in the rational design of dopant-free small molecular hole transport materials for high-performance perovskites solar cells is reviewed. The correlation between the molecular structure and device performance is elaborated.

Effects of subtle change in side chains on the photovoltaic performance of small molecular donors for solar cells

Small-molecule organic solar cells (SMOSCs) have attracted considerable attention owing to the merits of small molecules, such as easy purification, well-defined chemical structure. To achieve high-performance SMOSCs, the rational design of well-matched donor and acceptor materials is extremely essential. In this work, two new small molecular donor materials with subtle change in the conjugated side thiophene rings are synthesized. The subtle change significantly affects the photovoltaic performance of molecular donors. Compared with chlorinated molecule MDJ-Cl, the non-chlorinated analogue MDJ exhibits decreased miscibility with the non-fullerene acceptor Y6, can more efficiently quench the excitons of Y6. As a result, a improved PCE of 11.16% is obtained for MDJ:Y6 based SMOSCs. The results highlight the importance of fine-tuning the molecular structure to achieve high-performance SMOSCs.

Acridine Based Small Molecular Hole Transport Type Materials for Phosphorescent OLED Application.

Two small molecular hole-transporting type materials, namely 4-(9,9-dimethylacridin-10(9H)-yl)-N-(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)-N-phenylaniline (TPA-2ACR) and 10,10′-(9-phenyl-9H-carbazole-3,6-diyl)bis(9,9-dimethyl-9,10-dihydroacridine) (PhCAR-2ACR), were designed and synthesized using a single-step Buchwald–Hartwig amination between the dimethyl acridine and triphenylamine or carbazole moieties. Both materials showed high thermal decomposition temperatures of 402 and 422 °C at 5% weight reduction for PhCAR-2ACR and TPA-2ACR, respectively. TPA-2ACR as hole-transporting material exhibited excellent current, power, and external quantum efficiencies of 55.74 cd/A, 29.28 lm/W and 21.59%, respectively. The achieved device efficiencies are much better than that of the referenced similar, 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC)-based device (32.53 cd/A, 18.58 lm/W and 10.6%). Moreover, phenyl carbazole-based PhCAR-2ACR showed good device characteristics when applied for host material in phosphorescent OLEDs.

Construction of Large Non-Localized π-Electron System for Enhanced Sodium-Ion Storage.

Organic electrode materials with the advantages of renewability, environment-friendliness, low cost, and high capacity have received widespread attention in recent years for sodium-ion batteries. However, small molecular organic materials suffer from issues such as low conductivity and the high dissolution rate in electrolytes. Herein, a phthalocyanine derivative (TPcDS) with a large non-localized π-electron system, obtained through thermodynamic polymerization of 4-aminophthalonitrile (AP) monomers, is designed to address these issues. According to the density function theory calculation, six sodium ions can be attracted by one polymer molecule, indicating a high theoretical capacity of 375mAhg-1 . The TPcDS molecule realizes sodium storage through a non-localized π-electron system of phthalocyanine macrocycles. When employed as an anode material for sodium-ion batteries, the functional groups of phthalocyanine macrocycles, such as CN groups in TPcDS, experience obviously reversible structural variation upon discharge/charge. A high reversible capacity of 364mAhg-1 is achieved at a current density of 0.05Ag-1 , and a charge capacity of as high as 246mAhg-1 is still maintained after 500cycles at 0.1Ag-1 . This work provides an effective strategy for the design and synthesis of new oligomeric organic electrode materials.

Mapping the Regioisomeric Space and Visible Color Range of Purely Organic Dual Emitters with Ultralong Phosphorescence Components: From Violet to Red Towards Pure White Light.

We mapped the entire visible range of the electromagnetic spectrum and achieved white light emission (CIE: 0.31, 0.34) by combining the intrinsic ns‐fluorescence with ultralong ms‐phosphorescence from purely organic dual emitters. We realized small molecular materials showing high photoluminescence quantum yields (ΦL) in the solid state at room temperature, achieved by active exploration of the regioisomeric substitution space. Chromophore stacking‐supported stabilization of triplet excitons with assistance from enhanced intersystem crossing channels in the crystalline state played the primary role for the ultra‐long phosphorescence. This strategy covers the entire visible spectrum, based on organic phosphorescent emitters with versatile regioisomeric substitution patterns, and provides a single molecular source of white light with long lifetime (up to 163.5 ms) for the phosphorescent component, and high overall photoluminescence quantum yields (up to Φ L=20 %).

Mapping the Regioisomeric Space and Visible Color Range of Purely Organic Dual Emitters with Ultralong Phosphorescence Components: From Violet to Red Towards Pure White Light

AbstractWe mapped the entire visible range of the electromagnetic spectrum and achieved white light emission (CIE: 0.31, 0.34) by combining the intrinsic ns‐fluorescence with ultralong ms‐phosphorescence from purely organic dual emitters. We realized small molecular materials showing high photoluminescence quantum yields (ΦL) in the solid state at room temperature, achieved by active exploration of the regioisomeric substitution space. Chromophore stacking‐supported stabilization of triplet excitons with assistance from enhanced intersystem crossing channels in the crystalline state played the primary role for the ultra‐long phosphorescence. This strategy covers the entire visible spectrum, based on organic phosphorescent emitters with versatile regioisomeric substitution patterns, and provides a single molecular source of white light with long lifetime (up to 163.5 ms) for the phosphorescent component, and high overall photoluminescence quantum yields (up toΦL=20 %).