Different contents of fluorine in side alkyl chains were incorporated into three conjugated polymers (namely, PBDTTT-f13, PBDTTT-f9, and PBDTTT-f5) whose backbones consist of benzodithiophene donors and thienothiophene acceptors. These three fluorinated polymers, in comparison with the well-known analogue PTB7-Th, show comparable energy levels and optical band gaps. However, the fluorination of side alkyl chains significantly changed the surface energy of bulk materials, which leads to distinctly different self-assembly behaviors and phase separations as being mixed with PC71BM. The increased mismatch in surface energies between the polymer and PC71BM causes larger scale phase domains, which makes a sound explanation for the difference in their photovoltaic properties.Topics: Contact angle; Electric properties; Electric transport processes and properties; Electronic structure; Energy level; Heterojunction solar cells; Molecular structure-property relationship; Organic solar cells; Physical and chemical processes; Polymer morphology; Polymers; Quantum mechanics; Quantum mechanics; Self-assembly; Separation science; Spectra; Surface energy; Thin films; Thin films;

A series of tetradentate cyclometalated platinum(II) complexes (Pt 1, Pt 2, and Pt 3) based on 2-phenylbenzimidazole-containing ligands have been prepared. Their photophysical properties were investigated by absorption and emission spectroscopy as well as density functional theory calculations. Due to the robustness of their coordination frameworks, these Pt(II) complexes exhibited excellent thermal stabilities with decomposition temperatures above 400 °C. The 2-phenylbenzimidazole motif was functionalized with a twisted aryl group, which discouraged intimate intermolecular interactions, thus leading to constant CIE coordinates at different doping ratios. The effect of replacing a coordinating pyridine group by thiazole and oxazole on photophysical properties, electrochemical behaviors, and electroluminescence performance was studied. Single crystal X-ray diffraction analyses of Pt 1 revealed a weak intra-molecular interaction, particularly a negligible Pt⋯Pt interaction, in the solid state, which was consistent with its electroluminescence properties at a high doping level. Organic light emitting diodes (OLEDs) based on these Pt(II) complexes were fabricated with a typical multiple layered device configuration. Among the three Pt(II) complexes, the pyridine-based Pt 1 compound showed the highest electroluminescence performance with maximum CE, PE, and EQE of 78.5 cd A−1, 66.4 lm W−1, and 22.3%, respectively.

Two highly phosphorescent platinum(II) complexes (Pt1–Pt2) supported by spiro linkage-containing tetradentate ligands (L1–L2) were designed and prepared. The bulky spiro linkage was applied in these compounds to minimize the intermolecular Pt⋯Pt interaction and to suppress the formation of an excimer, thus leading to efficient electroluminescence. The picolinate coordination group was introduced into both L1 and L2 to bind Pt(II) ions. In L1, a pyridyl group serving as a coordination unit was attached to the spiro linkage; while in L2, an electron-rich functional group, N-methyl imidazole, was used. The molecular structures and packing patterns of these two Pt(II) complexes in the solid state were revealed by single-crystal X-ray diffraction measurements. The effect associated with the variation of coordination groups in Pt1–Pt2 on their photophysical and electroluminescence properties was studied. Organic light-emitting diodes (OLEDs) based on Pt1 and Pt2 were fabricated by the vacuum thermal evaporation approach. Both Pt1 and Pt2 showed yellowish green electro-phosphorescence with high efficiency. The device based on Pt1 at a doping ratio of 15 wt% achieved a maximum efficiency of 83.0 cd A−1, 63.8 lm W−1 and 22.9% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.36, 0.60) without any light extraction technologies. Remarkably, the EQE roll-off ratio of Pt2 at the doping level of 10 wt% from the peak value (20.2%) to that (19.5%) at a brightness of 1000 cd m−2 was 3.5%.

New-generation solar cells based on colloidal lead chalcogenide (PbX) quantum dots (CQDs) are promising low-cost solution-processed photovoltaics. However, current state-of-the art CQDs are all using an inverted device architecture. The performance gap between CQD solar cells with conventional and inverted structures is much larger than that for other solution-processed photovoltaics such as organic and perovskite solar cells, which may restrict the future development of CQD solar cells. Here, we reported a record-high power conversion efficiency of 8.45% for conventionally structured PbS QD solar cells by the introduction of a unique conjugated polymer PDTPBT as the anode buffer layer. With the modification of the anode, the device performance was largely improved through a dramatic enhancement in open circuit voltage (Voc), which can be attributed to the enhanced hole extraction to the anode after PDTPBT modification. Meanwhile, the polymer layer can also efficiently improve charge separation and reduce interfacial charge recombination as well as reverse saturation current density, which result in significantly enhanced Voc. More importantly, our results proposed a new conventional architecture for QD solar cells which can avoid the complex processing of metal oxides and is free of light-soaking. This new device structure may offer more flexibility in future device design and show potential advantages in large-scale manufacturing by simplifying the fabrication process.

•A new 2D-conjugated molecule DR3TBDTTVT was synthesized, and OSCs based on DR3TBDTTVT:PC71BM achieved a best PCE of 5.71%.•DR3TBDTTVT shows complementary absorption to PTB7-Th & PC71BM, and was introduced as third component to ternary OSCs.•The ternary OSCs displayed improved device performance compared with the binary OSCs based on PTB7-Th:PC71BM.Ternary organic solar cells (OSCs) are burgeoning as one of the effective strategies to achieve high power conversion efficiencies (PCEs) by incorporating a third component with a complementary absorption into the binary blends. In this study, we presented a new two-dimension-conjugated small molecule denoted by DR3TBDTTVT, which alone gave rise to a best PCE of 5.71% with acceptor PC71BM as active layer. Given the complementary absorption with PTB7-Th, DR3TBDTTVT was doped into (PTB7-Th:PC71BM)-based binary blends, and ternary OSCs were developed. The ternary OSCs with 10 wt% of DR3TBDTTVT displayed improved hole-mobility, reduced device resistance and better phase separation of active layer, thus leading to an impressive PCE of 7.77% with open-circuit voltage of 0.77 V, short-circuit density of 14.52 mA cm−2 and fill factor of 70.3%. Ternary OSCs well make up for the light-harvesting insufficiency of binary OSCs, and this research provides a new material for the improvement of PCEs for single-junction OSCs.Download high-res image (328KB)Download full-size image

•The big π system could enhance the thermal stability and the charge transport property of the host.•The limited conjugation length led to high triplet energies of host material.•High device performance was achieved due to the high ET and good bipolar charge transport properties.Four novel bipolar hosts, namely 9,9′-(2-(4,6-diphenylpyrimidin-2-yl)-1,3-phenylene)bis(9H-carbazole) (2CzPm), 9,9′-(2-(4,6-diphenylpyrimidin-2-yl)-1,3-phenylene)bis(3,6-di-tert-butyl-9H-carbazole) (2TCzPm), 5,5′-(2-(4,6-diphenylpyrimidin-2-yl)-1,3-phenylene)bis(5H-benzofuro[3,2-c]carbazole) (2BFCzPm) and 5,5′-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(5H-benzofuro[3,2-c]carbazole) (2BFCzTrz) were designed and synthesized with diphenylpyrimidine and diphenyltriazine as electron-transporting units and carbazole derivatives as hole-transporting motifs for the application in blue phosphorescent organic light-emitting diodes (PHOLEDs). These electron-accepting and -donating functional groups were attached to the central phenylene bridge in an ortho-substituted fashion, which led to high triplet energies (2.97–3.00 eV) and wide bandgap (3.43–3.55 eV). The effect of modulation of electron-accepting and donating groups on the photophysical properties, frontier orbital energy levels, charge carrier transport properties and device performance of these four hosts has been investigated. 2BFCzPm and 2BFCzTrz featured with large conjugation system exhibited high thermal stability as compared to 2CzPm and 2TCzPm. The bis[2-(4,6-difluorophenyl)-pyridinato-C2,N](picolinato)iridium(III) (FIrpic) based blue PHOLEDs hosted by 2BFCzPm exhibited excellent electroluminescence performance with a peak current efficiency of 38.2 cd/A and a maximum external quantum efficiency of 19.0%, which could be ascribed to the enhanced thermal stability, high triplet energy and good bipolar charge transport properties of the host material.A series of orthogonally substituted aryl derivatives has been prepared as bipolar hosts for high performance blue phosphorescent OLEDs.Download high-res image (172KB)Download full-size image

•Three Pt(II) emitters based on pyrazolo[1,5-f]phenanthridine-containing ligands were designed and synthesized.•The rigid motif led to the extremely high thermal stabilities of Pt(II) complexes.•ZPt1 showed high OLED performance, indicating its potential utility as an OLED phosphor.A series of highly luminescent [Pt(NˆCˆCˆN)] emitters (ZPt1, ZPt2 and ZPt3) based on pyrazolo[1,5-f]phenanthridine-containing ligands were designed and synthesized. These Pt(II) complexes demonstrated extremely high thermal stabilities with the 5% weight-reduction temperatures over 450 °C due to the incorporation of the rigid pyrazolo[1,5-f]phenanthridine motif and the robustness of the tetradentate coordination framework. These Pt(II) complexes have the same coordination set (pyridineˆbenzeneˆbenzeneˆpyrazole) but with slightly different linkage between coordination groups. Within ZPt1 and ZPt2, pyridine and the neighboring benzene groups are separated by oxygen and aniline, respectively. In ZPt3, pyridine group is rigidly grafted on the carbazole unit. The effect of the different linkages on the frontier orbital energies, the photophysical and electroluminescent properties of ZPt1-ZPt3 was investigated systematically. Organic light emitting diodes (OLEDs) based on these Pt(II) complexes were fabricated with typical device structure. The Pt(II) complexes displayed intense electroluminescence in the blue to yellowish green spectral region. Among the three Pt(II) complexes, the 3-(pyridin-2-yloxy)phenoxy-based ZPt1 compound showed the highest electroluminescence performance with the maximum CE, PE, and EQE of 58.0 cd A−1, 51.6 lm W−1, and 16.4%, respectively.A series of platinum(II) complexes based on pyrazolo[1,5-f]phenanthridine-containing ligands have been prepared for highly efficient phosphorescent OLEDs.Download high-res image (109KB)Download full-size image

•A simplified synthetic route for one dibenzo[g,p]chrysene derivative was developed.•Dibenzo[g,p]chrysene derivative was firstly used as host material with EQE of 14.4%.•BPAHs molecular platform has great potential in the construction of OLED materials.One polycyclic aromatic hydrocarbon compound, 3,6,11,14-tetraphenyldibenzo[g,p]chrysene (TPDBC), was designed, synthesized, and fabricated in a red phosphorescent organic light-emitting diode (PHOLED) with a maximum external quantum efficiency (EQE) of 14.4%, which represented the first report of a dibenzo[g,p]chrysene motif as the building block for host materials. It was conjectured that dibenzo[g,p]chrysene may serve as a next generation molecular platform which is readily functionalizable for the preparation of electroactive materials for applications in the emerging areas of molecular electronics.

Three blue-emitting Pt(II) complexes (Pt1, Pt2 and Pt3) supported by imidazo[1,2-f]phenanthridine-containing tetradentate ligands have been designed and prepared. A fused ring system, imidazo[1,2-f]phenanthridine, was introduced into these complexes to minimize the vibration and rotation of the ligand due to its rigidity, and the incorporation of this robust motif led to the high thermal stability of the resulting complexes. In addition, this efficient bidentate possesses high triplet energy (ET) to allow the preparation of blue-emitting complexes. A bulky mesityl group was attached to this rigid unit to reduce the strong intermolecular interaction and suppress the formation of an excimer in the solid state. Imidazo[1,2-f]phenanthridine was connected with three different pyridine^benzene bidentates to give the corresponding tetradentate ligands (L1, L2 and L3). In L1, the pyridine group was directly bonded to an N atom of a carbazole group; while in L2 and L3, the pyridine unit was linked to a benzene group via oxygen and spiro linkages, respectively. The introduction of a heteroatom linkage and spiro linkage into these tetradentate ligands would be effective in breaking the conjugation, leading to a wide bandgap and high ET. Despite the different linkages applied in the pyridine^benzene bidentates, complexes Pt1–Pt3 showed similar photoluminescence spectra with an intense emission peak at 460 nm. Organic light-emitting diodes (OLEDs) based on these complexes were fabricated by vacuum deposition with the typical device configuration. All these complexes showed blue electro-phosphorescence at various doping ratios. Among these Pt(II) complexes, Pt1 showed the highest OLED performance with a maximum CE, PE, and EQE of 36.5 cd A−1, 33.1 lm W−1, and 16.2%, respectively, with the CIE coordinates of (0.18, 0.32).

One of the most charming and challenging topics in organic chemistry is the selective C–H bond activation. The difficulty arises not only from the relatively large bond-dissociation enthalpy, but also from the poor reaction selectivity. In this work, Au(111) and Ag(111) surfaces were used to address ortho C–H functionalization and ortho-ortho couplings of phenol derivatives. More importantly, the competition between dehydrogenation and deoxygenation drove the diversity of reaction pathways of phenols on surfaces, that is, diselective ortho C–H bond activation on Au(111) surfaces and monoselective ortho C–H bond activation on Ag(111) surfaces. The mechanism of this unprecedented phenomenon was extensively explored by scanning tunneling microscopy, density function theory, and X-ray photoelectron spectroscopy. Our findings provide new pathways for surface-assisted organic synthesis via the mono/diselective C–H bond activation.

•The dependence of EL properties of Pt(II) complexes on the modulated coordination group is explored.•The series of Pt(II) complexes based on the unsymmetric tetradentate ligands shows flexible color tunability.•Efficient energy transfer from host to dopant is required to achieve high device performance.A new class of highly phosphorescent Pt(II) complexes (Pt1–Pt3) based on rigid unsymmetric tetradentate ligands (L1-L3) were designed and synthesized. L1-L3 ligands are an analogue to N,N-di(2-phenylpyrid-6-yl)aniline (L) except that one coordination phenyl group in L is replaced by other motifs with different electron donating/accepting capabilities. The effect associated with the modulation of a single coordination group within each ligand on the photophysical and electroluminescent properties of Pt1–Pt3 was investigated systematically. Among Pt1–Pt3, Pt1 has the highest HOMO due to the presence of a strong electron-donating group (3-methylindole), and exhibits the narrowest bandgap; Pt2 has the lowest HOMO due to the lack of strong donor group within the structure, and shows the widest bandgap. Organic light-emitting diodes (OLEDs) based on these three complexes showed yellowish green to greenish yellow electroluminescence with high efficiency. Notably, the device based on Pt1 at the doping level of 10 wt% achieved a maximum efficiency of 53.0 cd A−1, 35.9 lm W−1 and 16.3% with CIE coordinates of (0.44, 0.53).A series of rigid platinum(II) complexes based unsymmetric tetradentate ligands has been prepared as efficient dopants for high performance phosphorescent green/yellow OLEDs.

•The effect of DIO on the photovoltaic performance of polymer/PC71BM blends is studied.•The addition of DIO can optimize the morphology of the active layer and enhance hole and electron mobilities.•The impact of chalcogen atom on the intrinsic properties of donor materials has been studied.Two donor-acceptor polymers P8 and P9 based on 5,6-difluoro-benzo[1,2,5]thiadiazole unit have been prepared and applied as the donor materials in polymer solar cells. Due to the slight difference between electronic structures of thiophene and selenophene, P8 and P9 show similar absorption spectra and similar frontier energy levels. However, the pristine P8:PC71BM and P9:PC71BM blend films display distinct morphologies as revealed by AFM measurement. After the addition of DIO, both blend films feature a nanoscale interconnected-network structure, which leads to the enhancement in solar cells performance with PCE up to 6.73% and 6.84% for P8 and P9, respectively. Alternating current impedance spectrometry measurements revealed that high surface roughness could improve the PCE of P8-based PSCs, while in P9-based PSCs DIO can enhance hole and electron mobilities of the active layer.Two donor-acceptor polymers based on 5,6-difluoro-benzo[1,2,5]thiadiazole have been prepared as donor materials for high efficiency polymer solar cells.

A series of strongly phosphorescent Pt(II) complexes (Pt1–Pt3) supported by rigid benzazole-containing tetradentate ligands (L1–L3) were designed and synthesized. The effect of heteroatoms (S, O and N) on the photophysical and electroluminescence properties of Pt(II) complexes was studied systematically. Complex Pt1 based on the benzothiazole-containing ligand exhibited a red-shift in UV-vis and photoluminescence spectra in comparison with Pt2 and Pt3 due to the low electro-negativity and high polarizability of the S atom. Organic light-emitting diodes (OLEDs) with various doping levels of these Pt(II) phosphors were fabricated. At low complex concentration, Pt1, Pt2 and Pt3 mainly showed high energy monomer emission. When the doping ratio was increased, low energy excimer emission was observed for both Pt1 and Pt2. On the contrary, Pt3 dominantly showed monomer emission even at a high doping level because the strong intermolecular interactions were greatly suppressed due to the presence of bulky alkyl chains as revealed by X-ray crystallographic analysis. OLEDs based on these complexes exhibited yellowish green to greenish yellow electro-phosphorescence with high efficiency. Notably, the device based on Pt3 at the doping level of 10 wt% achieved a maximum efficiency of 75.0 cd A−1, 70.1 lm W−1 and 21.4% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.61).

•One of few reports about polymer materials for aprotic supercapacitors.•Hybridizing with Ketjenblack NPs improves the cycling stability of polymer.•Composite materials have large energy and power density.•Organic electrode materials are potentially renewable and low cost.Currently very few non-aqueous pseudocapacitor electrode materials are available. Organic matter based electrodes hold a great promise but remain largely unexplored. In this work, Ketjenblack carbon supported polyanthraquinone with different carbon to polymer ratios was prepared and evaluated as the pseudocapacitor electrode material in acetronitrile. These composite electrodes exhibit large specific capacitance up to 650 F/g and specific capacity up to 270 mAh/g when normalized to the polymer mass, which is much greater than other non-aqueous supercapacitor materials. They also have improved cycling stability with more than 85% capacitance retention after 1000 cycles as a result of the diminished quinone solubility in the electrolyte. When paired with a graphene-based positive electrode in asymmetric supercapacitors, composite electrodes demonstrate significant energy density up to 45.5 Wh/kg and power density up to 21.4 kW/kg. Their great supercapacitive performance, together with their low costs as well as structural and property diversities, makes them highly appealing for future energy storage applications.

A series of strongly phosphorescent Pt(II) complexes (Pt1–Pt3) supported by rigid benzazole-containing tetradentate ligands (L1–L3) were designed and synthesized. The effect of heteroatoms (S, O and N) on the photophysical and electroluminescence properties of Pt(II) complexes was studied systematically. Complex Pt1 based on the benzothiazole-containing ligand exhibited a red-shift in UV-vis and photoluminescence spectra in comparison with Pt2 and Pt3 due to the low electro-negativity and high polarizability of the S atom. Organic light-emitting diodes (OLEDs) with various doping levels of these Pt(II) phosphors were fabricated. At low complex concentration, Pt1, Pt2 and Pt3 mainly showed high energy monomer emission. When the doping ratio was increased, low energy excimer emission was observed for both Pt1 and Pt2. On the contrary, Pt3 dominantly showed monomer emission even at a high doping level because the strong intermolecular interactions were greatly suppressed due to the presence of bulky alkyl chains as revealed by X-ray crystallographic analysis. OLEDs based on these complexes exhibited yellowish green to greenish yellow electro-phosphorescence with high efficiency. Notably, the device based on Pt3 at the doping level of 10 wt% achieved a maximum efficiency of 75.0 cd A−1, 70.1 lm W−1 and 21.4% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.61).

Two highly phosphorescent platinum(II) complexes (Pt1–Pt2) supported by spiro linkage-containing tetradentate ligands (L1–L2) were designed and prepared. The bulky spiro linkage was applied in these compounds to minimize the intermolecular Pt⋯Pt interaction and to suppress the formation of an excimer, thus leading to efficient electroluminescence. The picolinate coordination group was introduced into both L1 and L2 to bind Pt(II) ions. In L1, a pyridyl group serving as a coordination unit was attached to the spiro linkage; while in L2, an electron-rich functional group, N-methyl imidazole, was used. The molecular structures and packing patterns of these two Pt(II) complexes in the solid state were revealed by single-crystal X-ray diffraction measurements. The effect associated with the variation of coordination groups in Pt1–Pt2 on their photophysical and electroluminescence properties was studied. Organic light-emitting diodes (OLEDs) based on Pt1 and Pt2 were fabricated by the vacuum thermal evaporation approach. Both Pt1 and Pt2 showed yellowish green electro-phosphorescence with high efficiency. The device based on Pt1 at a doping ratio of 15 wt% achieved a maximum efficiency of 83.0 cd A−1, 63.8 lm W−1 and 22.9% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.36, 0.60) without any light extraction technologies. Remarkably, the EQE roll-off ratio of Pt2 at the doping level of 10 wt% from the peak value (20.2%) to that (19.5%) at a brightness of 1000 cd m−2 was 3.5%.

A series of tetradentate cyclometalated platinum(II) complexes (Pt 1, Pt 2, and Pt 3) based on 2-phenylbenzimidazole-containing ligands have been prepared. Their photophysical properties were investigated by absorption and emission spectroscopy as well as density functional theory calculations. Due to the robustness of their coordination frameworks, these Pt(II) complexes exhibited excellent thermal stabilities with decomposition temperatures above 400 °C. The 2-phenylbenzimidazole motif was functionalized with a twisted aryl group, which discouraged intimate intermolecular interactions, thus leading to constant CIE coordinates at different doping ratios. The effect of replacing a coordinating pyridine group by thiazole and oxazole on photophysical properties, electrochemical behaviors, and electroluminescence performance was studied. Single crystal X-ray diffraction analyses of Pt 1 revealed a weak intra-molecular interaction, particularly a negligible Pt⋯Pt interaction, in the solid state, which was consistent with its electroluminescence properties at a high doping level. Organic light emitting diodes (OLEDs) based on these Pt(II) complexes were fabricated with a typical multiple layered device configuration. Among the three Pt(II) complexes, the pyridine-based Pt 1 compound showed the highest electroluminescence performance with maximum CE, PE, and EQE of 78.5 cd A−1, 66.4 lm W−1, and 22.3%, respectively.