Showing papers on "HOMO/LUMO published in 2016"
TL;DR: The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices.
Abstract: Fine energy-level modulations of small-molecule acceptors (SMAs) are realized via subtle chemical modifications on strong electron-withdrawing end-groups. The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices. Finally, a top power conversion efficiency of 12.05% is achieved.
1,276 citations
TL;DR: Ultrapure blue-fluorescent molecules based on thermally activated delayed fluorescence are developed that exhibit a deep blue emission at 467 nm with a full-width at half-maximum of 28 nm and an internal quantum efficiency of ≈100%, which represent record-setting performance for blue OLED devices.
Abstract: Ultrapure blue-fluorescent molecules based on thermally activated delayed fluorescence are developed. Organic light-emitting diode (OLED) devices employing the new emitters exhibit a deep blue emission at 467 nm with a full-width at half-maximum of 28 nm, CIE coordinates of (0.12, 0.13), and an internal quantum efficiency of ≈100%, which represent record-setting performance for blue OLED devices.
917 citations
TL;DR: An efficient fused-ring electron acceptor based on indacenodithieno[3,2-b]thiophene core and thienyl side-chains for organic solar cells (OSCs) is developed and rivals some of the highest efficiencies for single junction OSCs based on fullerene acceptors.
Abstract: We develop an efficient fused-ring electron acceptor (ITIC-Th) based on indacenodithieno[3,2-b]thiophene core and thienyl side-chains for organic solar cells (OSCs). Relative to its counterpart with phenyl side-chains (ITIC), ITIC-Th shows lower energy levels (ITIC-Th: HOMO = −5.66 eV, LUMO = −3.93 eV; ITIC: HOMO = −5.48 eV, LUMO = −3.83 eV) due to the σ-inductive effect of thienyl side-chains, which can match with high-performance narrow-band-gap polymer donors and wide-band-gap polymer donors. ITIC-Th has higher electron mobility (6.1 × 10–4 cm2 V–1 s–1) than ITIC (2.6 × 10–4 cm2 V–1 s–1) due to enhanced intermolecular interaction induced by sulfur–sulfur interaction. We fabricate OSCs by blending ITIC-Th acceptor with two different low-band-gap and wide-band-gap polymer donors. In one case, a power conversion efficiency of 9.6% was observed, which rivals some of the highest efficiencies for single junction OSCs based on fullerene acceptors.
892 citations
TL;DR: A novel non-fullerene acceptor, possessing a very low bandgap of 1.34 eV and a high-lying lowest unoccupied molecular orbital level of -3.95 eV, is designed and synthesized by introducing electron-donating alkoxy groups to the backbone of a conjugated small molecule.
Abstract: A novel non-fullerene acceptor, possessing a very low bandgap of 1.34 eV and a high-lying lowest unoccupied molecular orbital level of -3.95 eV, is designed and synthesized by introducing electron-donating alkoxy groups to the backbone of a conjugated small molecule. Impressive power conversion efficiencies of 8.4% and 10.7% are obtained for fabricated single and tandem polymer solar cells.
413 citations
TL;DR: Electrochemical findings showed that inhibitors impart high resistance towards charge transfer across the metal-electrolyte interface and behaved as mixed type inhibitors.
Abstract: In order to evaluate the effect of the functional group present in the ligand backbone towards corrosion inhibition performances, three Schiff-base molecules namely, (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)pyridine (L(1)), (E)-4-(2-(pyridin-4-ylmethylene)hydrazinyl)benzonitrile (L(2)) and (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)phenol (L(3)) were synthesized and used as corrosion inhibitors on mild steel in 1 M HCl medium. The corrosion inhibition effectiveness of the studied inhibitors was investigated by weight loss and several sophisticated analytical tools such as potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Experimentally obtained results revealed that corrosion inhibition efficiencies followed the sequence: L(3) > L(1) > L(2). Electrochemical findings showed that inhibitors impart high resistance towards charge transfer across the metal-electrolyte interface and behaved as mixed type inhibitors. Scanning electron microscopy (SEM) was also employed to examine the protective film formed on the mild steel surface. The adsorption as well as inhibition ability of the inhibitor molecules on the mild steel surface was investigated by quantum chemical calculation and molecular dynamic (MD) simulation. In quantum chemical calculations, geometry optimized structures of the Schiff-base inhibitors, electron density distribution in HOMO and LUMO and Fukui indices of each atom were employed for their possible mode of interaction with the mild steel surfaces. MD simulations revealed that all the inhibitors molecules adsorbed in parallel orientation with respect to the Fe(110) surface.
352 citations
TL;DR: ATT-1 Bulk-heterojunction (BHJ) solar cells based on PTB7-Th electron donor and ATT-1 electron acceptor delivered power conversion efficiencies of up to 10.07%, which is among the best performances reported for non-fullerene BHJ solar cells using PTB 7-Th as the electron donor.
Abstract: A thieno[3,4-b]thiophene-based electron acceptor, ATT-1, is designed and synthesized. ATT-1 exhibits a planar conjugated framework, broad absorption with a large absorption coefficient, and a slightly high LUMO energy level. Bulk-heterojunction (BHJ) solar cells based on PTB7-Th electron donor and ATT-1 electron acceptor delivered power conversion efficiencies of up to 10.07%, which is among the best performances reported for non-fullerene BHJ solar cells using PTB7-Th as the electron donor.
280 citations
TL;DR: Nitrogen-functionalized graphene quantum dots with tailorable optical properties are prepared by a versatile technique, which allows the highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels and energy gaps to be continuously varied.
Abstract: Nitrogen-functionalized graphene quantum dots (NGQDs) with tailorable optical properties are prepared by a versatile technique, which allows the highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels and energy gaps to be continuously varied. The integration of NGQD layers into the structures significantly improves the performance of optoelectronic devices.
210 citations
TL;DR: Preliminary all-polymer solar cell (all-PSC) devices with P-BNBP-T as the electron acceptor and PTB7As the electron donor exhibit a power conversion efficiency (PCE) of 3.38%, which is among the highest values of all-PSCs with PTB 7 as the electrons donor.
Abstract: A double B←N bridged bipyridyl (BNBP) is a novel electron-deficient building block for polymer electron acceptors in all-polymer solar cells. The B←N bridging units endow BNBP with fixed planar configuration and low-lying LUMO/HOMO energy levels. As a result, the polymer based on BNBP units (P-BNBP-T) exhibits high electron mobility, low-lying LUMO/HOMO energy levels, and strong absorbance in the visible region, which is desirable for polymer electron acceptors. Preliminary all-polymer solar cell (all-PSC) devices with P-BNBP-T as the electron acceptor and PTB7 as the electron donor exhibit a power conversion efficiency (PCE) of 3.38 %, which is among the highest values of all-PSCs with PTB7 as the electron donor.
208 citations
TL;DR: In this article, the potential of zero charge (E pzc) was also determined for evaluation of the adsorption mechanism of mild steel in 2M HCl solution by means of weight loss, polarization, electrochemical impedance spectroscopy and scanning electron microscopy.
201 citations
TL;DR: It has been found that surface-passivation of the as-prepared CDs by nitrogen doping can improve the emission efficiency and be beneficial to EIE features due to the single electron transition resulting from the single functional groups.
Abstract: Surface states of carbon dots (CDs) are critical to the photoemission properties of CDs. By carefully adjusting the reaction conditions in a hydrothermal synthesis route, we have prepared a series of CDs with excitation-dependent emission (EDE) and excitation-independent emission (EIE) properties by controlling the content of nitrogen elements, confirming that the characteristic optical properties of CDs originate from their energy levels. It has been found that surface-passivation of the as-prepared CDs by nitrogen doping can improve the emission efficiency and be beneficial to EIE features due to the single electron transition resulting from the single functional groups. And the as-prepared CDs can specifically bind with Hg2+ with the emission quenched because of the electron transfer from the LUMO levels of CDs to Hg2+.
193 citations
TL;DR: It is found that the nonlinear transfer curves can be tuned to near-ideal ones by changing fabrication conditions, indicating that film morphology largely contributes to the non linear transfer curves in high-mobility conjugated polymers.
Abstract: Planar backbone, locked conformation, and low lowest unoccupied molecular orbital level provide polymer F4 BDOPV-2T with ultrahigh electron mobilities of up to 14.9 cm(2) V(-1) s(-1) and good air stability. It is found that the nonlinear transfer curves can be tuned to near-ideal ones by changing fabrication conditions, indicating that film morphology largely contributes to the nonlinear transfer curves in high-mobility conjugated polymers.
TL;DR: In this article, a comprehensive study on the GERS effect of pristine graphene and nitrogen-doped graphene is presented, and it is shown that nitrogen-Doped graphene has enormous potential as a substrate when detecting low concentrations of molecules and could also allow for an effective identification of their HOMO-LUMO gaps.
Abstract: As a novel and efficient surface analysis technique, graphene-enhanced Raman scattering (GERS) has attracted increasing research attention in recent years. In particular, chemically doped graphene exhibits improved GERS effects when compared with pristine graphene for certain dyes, and it can be used to efficiently detect trace amounts of molecules. However, the GERS mechanism remains an open question. We present a comprehensive study on the GERS effect of pristine graphene and nitrogen-doped graphene. By controlling nitrogen doping, the Fermi level (EF) of graphene shifts, and if this shift aligns with the lowest unoccupied molecular orbital (LUMO) of a molecule, charge transfer is enhanced, thus significantly amplifying the molecule’s vibrational Raman modes. We confirmed these findings using different organic fluorescent molecules: rhodamine B, crystal violet, and methylene blue. The Raman signals from these dye molecules can be detected even for concentrations as low as 10−11 M, thus providing outstanding molecular sensing capabilities. To explain our results, these nitrogen-doped graphene-molecule systems were modeled using dispersion-corrected density functional theory. Furthermore, we demonstrated that it is possible to determine the gaps between the highest occupied and the lowest unoccupied molecular orbitals (HOMO-LUMO) of different molecules when different laser excitations are used. Our simulated Raman spectra of the molecules also suggest that the measured Raman shifts come from the dyes that have an extra electron. This work demonstrates that nitrogen-doped graphene has enormous potential as a substrate when detecting low concentrations of molecules and could also allow for an effective identification of their HOMO-LUMO gaps.
TL;DR: The slim orbital overlap between HOMO and LUMO and hence the lack of electron correlation lead to a significant reduction of the energy gap between the lowest lying singlet and triplet excited states (ΔET-S ) and thereby the generation of thermally activated delay fluorescence (TADF).
Abstract: The electron positive boron atom usually does not contribute to the frontier orbitals for several lower-lying electronic transitions, and thus is ideal to serve as a hub for the spiro linker of light-emitting molecules, such that the electron donor (HOMO) and acceptor (LUMO) moieties can be spatially separated with orthogonal orientation. On this basis, we prepared a series of novel boron complexes bearing electron deficient pyridyl pyrrolide and electron donating phenylcarbazolyl fragments or triphenylamine. The new boron complexes show strong solvent-polarity dependent charge-transfer emission accompanied by a small, non-negligible normal emission. The slim orbital overlap between HOMO and LUMO and hence the lack of electron correlation lead to a significant reduction of the energy gap between the lowest lying singlet and triplet excited states (ΔET-S ) and thereby the generation of thermally activated delay fluorescence (TADF).
TL;DR: In this paper, two conjugated copolymers, HSL1 and HSL2, were developed and applied as hole selective layers to improve the anode interface of fullerene/perovskite planar heterojunction solar cells.
Abstract: Two chemically tailored new conjugated copolymers, HSL1 and HSL2, were developed and applied as hole selective layers to improve the anode interface of fullerene/perovskite planar heterojunction solar cells. The introduction of polar functional groups on the polymer side chains increases the surface energy of the hole selective layers (HSLs), which promote better wetting with the perovskite films and lead to better films with full coverage and high crystallinity. The deep highest occupied molecular orbital levels of the HSLs align well with the valence band of the perovskite semiconductors, resulted in increase photovoltage. The high lying lowest unoccupied molecule orbital level provides sufficient electron blocking ability to prevent electrons from reaching the anode and reduces the interfacial trap-assisted recombination at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/perovskite interface, resulting in a longer charge-recombination lifetime and shorter charge-extraction time. In the presence of the HSLs, high-performance CH3NH3PbI x Cl3− x perovskite solar cells with a power conversion efficiency (PCE) of 16.6% (V oc: 1.07 V) and CH3NH3Pb(I0.3Br0.7) x Cl3− x cells with a PCE of 10.3% (V oc: 1.34 V) can be realized.
TL;DR: In this article, the adsorption and corrosion inhibition properties of three piperidine derivatives, namely, (1-(5-fluoro-2-(methylthio) pyrimidine-4-yl)-piperidine 4-yl), (1.5-5-dimethoxybenzenesulfonamide (FMPPDBS) and FMPPNBS, on the corrosion of iron were investigated by performing quantum chemical calculations and molecular dynamics simulations.
Abstract: The adsorption and corrosion inhibition properties of three piperidine derivatives namely, (1-(5-fluoro-2-(methylthio) pyrimidine-4-yl) piperidine-4-yl)-2,5-dimethoxybenzenesulfonamide (FMPPDBS), (1-(5-fluoro-2-(methylthio) pyrimidine-4-yl) piperidine-4-yl)-4-nitrobenzenesulfonamide (FMPPNBS), (1-(5-fluoro-2-(methylthio) pyrimidine-4-yl) piperidine-4-yl)-3-methoxybenzenesulfonamide (FMPPMBS) on the corrosion of iron were investigated by performing quantum chemical calculations and molecular dynamics simulations. Global reactivity parameters such as E HOMO , E LUMO , HOMO–LUMO energy gap (∆ E ), chemical hardness, softness, electronegativity, proton affinity, electrophilicity and nucleophilicity have been calculated and discussed. The adsorption behaviors of these piperidine derivatives on Fe(110), Fe(100) and Fe(111) surfaces were investigated using molecular dynamics simulation. The binding energies on metal surface of studied compounds followed the order: FMPPDBS > FMPPMBS> FMPPNBS and this ranking obtained is consistent with the experimental data.
TL;DR: This study highlights that the aromatic ligands not only lead to a higher conversion in catalytic reaction but also markedly increase the yield of the heterocoupling product (4-methyl-4'-nitro-1,1'-biphenyl).
Abstract: To explore the electronic and catalytic properties of nanoclusters, here we report an aromatic-thiolate-protected gold nanocluster, [Au25(SNap)18]− [TOA]+, where SNap = 1-naphthalenethiolate and TOA = tetraoctylammonium. It exhibits distinct differences in electronic and catalytic properties in comparison with the previously reported [Au25(SCH2CH2Ph)18]−, albeit their skeletons (i.e., Au25S18 framework) are similar. A red shift by ∼10 nm in the HOMO–LUMO electronic absorption peak wavelength is observed for the aromatic-thiolate-protected nanocluster, which is attributed to its dilated Au13 kernel. The unsupported [Au25(SNap)18]− nanoclusters show high thermal and antioxidation stabilities (e.g., at 80 °C in the present of O2, excess H2O2, or TBHP) due to the effects of aromatic ligands on stabilization of the nanocluster’s frontier orbitals (HOMO and LUMO). Furthermore, the catalytic activity of the supported Au25(SR)18/CeO2 (R = Nap, Ph, CH2CH2Ph, and n-C6H13) is examined in the Ullmann heterocoupling r...
TL;DR: In this paper, the authors proposed a twisted-ICT framework for a flattened molecular backbone and introduced a strong acceptor possessing nπ* transition character, hypsochromic color, a large radiative rate (kF), and small singlet-triplet splitting energy (ΔEST) for reverse intersystem crossing from nonemissive triplet state to radiative singlet state.
Abstract: A barely reached balance between weak intramolecular-charge-transfer (ICT) and small singlet–triplet splitting energy (ΔEST) for reverse intersystem crossing from non-emissive triplet state to radiative singlet state impedes the realization of deep-blue thermally activated delayed fluorescence (TADF) materials. By discarding the twisted-ICT framework for a flattened molecular backbone and introducing a strong acceptor possessing n–π* transition character, hypsochromic color, a large radiative rate (kF), and small ΔEST are achieved simultaneously. Six molecules with a 9,9-dimethyl-10-phenyl-9,10-dihydroacridine (i-DMAc) donor are synthesized and investigated. Coinciding with time-dependent density functional theory, the reduced dihedral angles between donor (D) and acceptor (A) weaken ICT from dispersed charge density and enable a large kF from increased frontier molecular orbitals overlap. Despite the separated highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) population, the intercalation of phenyl bridges between D–A increases kF but significantly lowers the local triplet excited state, indicating small HOMO and LUMO overlap is not a sufficient, but necessary condition for reduced ΔEST. Integrating short conjugation length and carbonyl or triazine acceptors into the complanation molecules, deep-blue TADF organic light-emitting diodes demonstrate maximum external quantum efficiencies of 11.5% and 10.9% with Commission Internationale de l'Eclairage coordinates of (0.16, 0.09) and (0.15, 0.11), respectively, which is quite close to the stringent National Television System Committee blue standard.
TL;DR: The efficient p-doping of the donor-acceptor dithienyl-diketopyrrolopyrrole-based copolymer having the highest unoccupied molecular orbital level of -5.49 eV is achieved.
Abstract: [3]-Radialene-based dopant CN6-CP studied herein, with its reduction potential of +0.8 versus Fc/Fc+ and the lowest unoccupied molecular orbital level of -5.87 eV, is the strongest molecular p-dopant reported in the open literature, so far. The efficient p-doping of the donor-acceptor dithienyl-diketopyrrolopyrrole-based copolymer having the highest unoccupied molecular orbital level of -5.49 eV is achieved. The doped films exhibit electrical conductivities up to 70 S cm(-1) .
TL;DR: In this article, the authors studied the methodologies of searching for novel organic charge transfer binary compounds and large-size crystal growth, in the case that only the two starting organic substances are known but the phase diagram is not known, the thermodynamic data of the binary compound are not known.
Abstract: The methodologies of searching for novel organic charge transfer binary compounds and large-size crystal growth, in the case that only the two starting organic substances are known but the phase diagram is not known, the thermodynamic data of the binary compound are not known, and even the existence of new binary compounds is not known, were studied. Centimeter-long crystals of novel perylene-F1TCNQ, perylene-F2TCNQ, and perylene-F4TCNQ charge transfer binary compounds are obtained from the gas phase. Kinetically lowering the sublimation rate is the key factor for growing large-size charge transfer compound single crystals. Changing the number of fluorine atoms in FxTCNQ results in the variation of the electron affinity, which further changes the HOMO–LUMO of acceptor. Charge transfer degree is increased with increasing of fluorine atoms in the perylene-FxTCNQ system. Therefore, the structure, stoichiometry, and kind of donor and acceptor enable HOMO–LUMO engineering of the charge transfer compound and tu...
TL;DR: The state-of-the-art in organocatalytic dienamine activation of enals is outlined and discussed, classifying examples according to different reactive activation pathways.
Abstract: Chiral secondary amines are some of the most commonly used kinds of catalysts. They have become a reliable tool for the α- and β-activation of carbonyl compounds, via HOMO, SOMO or LUMO activation pathways. Recently, chemists have turned their attention to the development of novel organocatalytic strategies for remote functionalisation, targeting stereocentres even more distant from the catalyst-activation site, through dienamine, trienamine, and vinylogous iminium ion pathways (γ-, e- and δ-positions, respectively). Here we outline and discuss the state-of-the-art in dienamine activation, classifying examples according to the different reactive activation pathways followed by the formed dienamine intermediate (1,3-, 1,5-, 2,5- and 4,5-functionalisation) and the reaction type developed, as determined by the structure and the nature of electrophiles and nucleophiles.
TL;DR: A new design strategy and reliable calculation methods are offered towards the development of excellent organic small molecules as HTMs for highly efficient and stable PSCs and, taking into consideration the appropriate HOMO level, improved hole mobility and enhanced stability, Spiro-F1 and Spira-F3 may become the most promising alternatives toSpiro-OMeTAD.
Abstract: Perovskite solar cells (PSCs) with organic small molecules as hole transport materials (HTMs) have attracted considerable attention due to their power conversion efficiencies as high as 20%. In the present work, three new spiro-type hole transport materials with spiro-cores, i.e. Spiro-F1, Spiro-F2 and Spiro-F3, are investigated by using density functional theory combined with the Marcus theory and Einstein relation. Based on the calculated and experimental highest occupied molecular orbital (HOMO) levels of 30 reference molecules, an empirical equation, which can predict the HOMO levels of hole transport materials accurately, is proposed. Moreover, a simplified method, in which the hole transport pathways are simplified to be one-dimensional, is presented and adopted to qualitatively compare the molecular hole mobilities. The calculated results show that the perovskite solar cells with the new hole transport materials can have higher open-circuit voltages due to the lower HOMO levels of Spiro-F1 (-5.31 eV), Spiro-F2 (-5.42 eV) and Spiro-F3 (-5.10 eV) compared with that of Spiro-OMeTAD (-5.09 eV). Furthermore, the hole mobilities of Spiro-F1 (1.75 × 10(-2) cm(2) V(-1) s(-1)) and Spiro-F3 (7.59 × 10(-3) cm(2) V(-1) s(-1)) are 3.1 and 1.4 times that of Spiro-OMeTAD (5.65 × 10(-3) cm(2) V(-1) s(-1)) respectively, due to small reorganization energies and large transfer integrals. Interestingly, the stability properties of Spiro-F1 and Spiro-F2 are shown to be comparable to that of Spiro-OMeTAD, and the dimers of Spiro-F2 and Spiro-F3 possess better stability than that of Spiro-OMeTAD. Taking into consideration the appropriate HOMO level, improved hole mobility and enhanced stability, Spiro-F1 and Spiro-F3 may become the most promising alternatives to Spiro-OMeTAD. The present work offers a new design strategy and reliable calculation methods towards the development of excellent organic small molecules as HTMs for highly efficient and stable PSCs.
TL;DR: In this article, the authors used density functional theory (DFT) calculations and molecular dynamics simulations approach to predict corrosion inhibition performances of 2-amino-4-(4-chlorophenyl)-thiazole derivatives against corrosion of Fe metal.
TL;DR: New π-conjugated polymers (PBTD4T and PBDTD4T) incorporating thienoquinoids 2,2'-bithiophene-5,5'-dione (BTD) and benzo[1,2-b:4,5-b']dithyphene-2,6-dione(BDTD) as strong electron-deficient (acceptor) units are synthesized.
Abstract: The introduction of quinoidal character to π-conjugated polymers is one of the effective approaches to reducing the bandgap. Here we synthesized new π-conjugated polymers (PBTD4T and PBDTD4T) incorporating thienoquinoids 2,2′-bithiophene-5,5′-dione (BTD) and benzo[1,2-b:4,5-b′]dithiophene-2,6-dione (BDTD) as strong electron-deficient (acceptor) units. PBTD4T showed a deep LUMO energy level of −3.77 eV and a small bandgap of 1.28 eV, which are similar to those of the analog using thieno[3,2-b]thiophene-2,5-dione (TTD) (PTTD4T). PBDTD4T had a much deeper LUMO energy level of −4.04 eV and a significantly smaller bandgap of 0.88 eV compared to those of the other two polymers. Interestingly, PBDTD4T showed high transparency in the visible region. The very small bandgap of PBDTD4T can be rationalized by the enhanced contribution of the resonance backbone structure in which the p-benzoquinodimethane skeleton in the BDTD unit plays a crucial role. PBTD4T and PBDTD4T exhibited ambipolar charge transport with more ...
TL;DR: The results showed that PP3 is the best corrosion inhibitor among the three compounds studied and the inhibition efficiency increases with an increase in concentration for all the inhibitors as discussed by the authors, and the adsorption of inhibitor molecules on mild steel surface was found to be spontaneous and obeyed the Langmuir adsorment isotherm.
TL;DR: The results demonstrate that PDI derivatives with a three dimensional molecular structure could serve as high performance electron acceptors in BHJSCs.
TL;DR: A new polymer acceptor based on the BNBP unit with an optimal LUMO energy level has been developed and the resulting all-polymer solar cells show high PCEs, remarkably high Voc values and small photon energy losses.
Abstract: A key parameter for polymer electron acceptors is the lowest unoccupied molecular orbital (LUMO) energy level (ELUMO). For state-of-the-art polymer electron acceptors based on the naphthalene diimide (NDI) unit, their ELUMO are low-lying and cannot be tuned, leading to a low open-circuit voltage (Voc) of the resulting all-polymer solar cells (all-PSCs). We report that polymer electron acceptors based on the double B←N bridged bipyridine (BNBP) unit exhibit tunable ELUMO because of their delocalized LUMOs over polymer backbones. The ELUMO of the copolymer of the BNBP unit and selenophene unit (P-BNBP-Se) is lower by 0.16 eV than that of the copolymer of the BNBP unit and thiophene unit (P-BNBP-T). As a result, the energy levels of P-BNBP-Se match well with the widely-used polymer donor, poly[(ethylhexyl-thiophenyl)-benzodithiophene-(ethylhexyl)-thienothiophene] (PTB7-Th). The electron mobility of P-BNBP-Se (μe = 2.07 × 10−4 cm2 V−1 s−1) is also higher than that of P-BNBP-T (μe = 7.16 × 10−5 cm2 V−1 s−1). While the all-PSC device based on the PTB7-Th:P-BNBP-T blend shows a moderate power conversion efficiency (PCE) of 2.27%, the corresponding device with P-BNBP-Se as the acceptor exhibits a PCE as high as 4.26%. Moreover, owing to the suitable ELUMO of P-BNBP-Se, the all-PSC device of P-BNBP-Se shows a Voc up to 1.03 V, which is higher by 0.22 V than that with the conventional NDI-based polymer acceptor. These results indicate that BNBP-based polymers can give all-PSCs with high PCEs, remarkably high Voc values and small photon energy losses.
TL;DR: Lowering the LUMOs and decreasing energy “waste” is targeted through inserting an auxiliary group from an electron donor or acceptor into D–π–A organic sensitizers, and the photovoltaic efficiency increases 38 fold.
Abstract: In dye-sensitized solar cells (DSSCs), the HOMO–LUMO energy gap of organic sensitizers should be large enough to enable efficient electron injection and dye regeneration. However, the LUMOs of most practical organic dyes are always too high, making energy “waste”. In order to deepen the LUMOs, we focus on the targeted modulation of the molecular energy levels by embedding an electron donor or acceptor into the skeleton of a typical D–π–A model. The electron-rich group of 3,4-ethylenedioxythiophene (EDOT) lifts up the HOMO level with little influence on the LUMO, while the electron-deficient group of benzothiadiazole (BTD) or benzooxadiazole (BOD) mainly lowers the customized LUMO level. As a consequence, the auxiliary group change from EDOT (dye WS-53) to BOD (dye WS-55) brings forth a huge photoelectric conversion efficiency (PCE) increase by 38 fold from 0.24 to 9.46% based on an I−/I3− redox couple, and even reaching a high PCE of 10.14% with WS-55 under 0.3 sunlight irradiation.
TL;DR: The low LUMO level and the conformation-locked planar backbone provide polymer AzaBDOPV-2T with electron mobilities over 3.22 cm2 V–1 s–1 tested in air.
Abstract: With sp2-nitrogen atoms embedded in an isatin unit, a donor–acceptor (D–A) conjugated polymer AzaBDOPV-2T was developed with a low LUMO level down to −4.37 eV. The lowered LUMO level as well as the conformation-locked planar backbone provide AzaBDOPV-2T with electron mobilities over 3.22 cm2 V−1 s−1 tested under ambient conditions, which is among the highest in n-type polymer field-effect transistors (FETs). Our results demonstrate that embedding electron-deficient sp2-nitrogen in conjugated backbones is an effective approach to develop n-type polymer semiconductors with high performance.
TL;DR: In this article, a polythiophene derivative donor with a low HOMO level of −5.6 eV was synthesized by copolymerizing carboxylate- and fluorine-substituted thiophene alternately.
Abstract: The fine alignment of molecular energy levels can efficiently enhance the open-circuit voltage (VOC) and improve the photovoltaic performance of polymer solar cells (PSCs). In this work, a novel polythiophene derivative donor with a low HOMO level of −5.6 eV was synthesized by copolymerizing carboxylate- and fluorine-substituted thiophene alternately. The introduction of fluorine downshifted the HOMO level of the polymer. On the other hand, a methyl-end-capped ITIC derivative, with elevated HOMO and LUMO levels, was selected as the acceptor in the pursuit of a higher VOC. A best power conversion efficiency (PCE) of 6.6% with an extremely high VOC of 1.13 V can be obtained after careful morphology optimization. Besides, an unprecedented energy loss of 0.46 eV is seen in this device, which is comparable to perovskite solar cells and has been rarely achieved before in bulk heterojunction PSCs.
TL;DR: In this paper, the synthesis of various functionalized azulene derivatives is summarized and their applications in optoelectronics are discussed, with particular attention to the fields including nonlinear optics (NLO), organic field effect transistors (OFETs), solar cells, and molecular devices.