ABSTRACT
The power conversion efficiency (PCE) of organic photovoltaics (OPVs) has reached more than 19% due to the rapid development of non-fullerene acceptors (NFAs). To compete with the PCEs (26%) of commercialized silicon-based inorganic photovoltaics, the drawback of OPVs should be minimized. This drawback is the intrinsic large loss of open-circuit voltage; however, a general approach to this issue remains elusive. Here, we report a discovery regarding highly efficient NFAs, specifically ITIC. We found that charge-transfer (CT) and charge dissociation (CD) can occur even in a neat ITIC film without the donor layer. This is surprising, as these processes were previously believed to take place exclusively at donor/acceptor heterojunctions. Femtosecond time-resolved visible to mid-infrared measurements revealed that in the neat ITIC layers, the intermolecular CT immediately proceeds after photoirradiation (<0.1 ps) to form weakly-bound excitons with a binding energy of 0.3 eV, which are further dissociated into free electrons and holes with a time-constant of 56 ps. Theoretical calculations indicate that stacking faults in ITIC (i.e., V-type molecular stacking) induce instantaneous intermolecular CT and CD in the neat ITIC layer. In contrast, J-type stacking does not support such CT and CD. This previously unknown pathway is triggered by the larger dipole moment change on the excited state generated at the lower symmetric V-type molecular stacking of ITIC. This is in sharp contrast with the need of sufficient energy offset for CT and CD at the donor-acceptor heterojunction, leading to the significant voltage loss in conventional OPVs. These results demonstrate that the rational molecular design of NFAs can increase the local dipole moment change on the excited state within the NFA layer. This finding paves the way for a groundbreaking route toward the commercialization of OPVs.
ABSTRACT
In dye-sensitized solar cells (DSSCs), flat planar dyes (e. g., highly light-harvesting porphyrins and corroles) with multiple anchoring groups are known to adopt a horizontal orientation on TiO2 through the multiple binding to TiO2. Due to the strong electronic coupling between the dye and TiO2, fast charge recombination between the oxidized dye and an electron in TiO2 occurs, lowering the power conversion efficiency (η). To overcome this situation, an additional donor moiety can be placed on top of the planar dye on TiO2 to slow down the undesirable charge recombination. Here we report the synthesis and photovoltaic properties of a triarylamine (TAA)-tethered gold(III) corrole (TAA-AuCor). The DSSC with TAA-AuCor using iodine redox shuttle exhibited the highest η-value among corrole-based DSSCs, which is much higher than that with the reference AuCor. The transient absorption spectroscopies clearly demonstrated that fast electron transfer from the TAA moiety to the corrole radical cation in TAA-AuCor competes with the undesirable charge recombination to generate long-lived charge separated state TAAâ +-Cor/TiO2â - efficiently. Consequently, the introduction of the TAA moiety enhanced the η-value remarkably, demonstrating the usefulness of our new concept to manipulate charge-separated states toward highly efficient DSSCs.
ABSTRACT
Precise engineering of excited-state interactions between an organic conjugated molecule and a two-dimensional semiconducting inorganic nanosheet, specifically the manipulation of charge-transfer excited (CTE) states, still remains a challenge for state-of-the-art photochemistry. Herein, we report a long-lived, highly emissive CTE state at structurally well-defined hetero-nanostructure interfaces of photoactive pyrene and two-dimensional MoS2 nanosheets via an N-benzylsuccinimide bridge (Py-Bn-MoS2). Spectroscopic measurements reveal that no charge-transfer state is formed in the ground state, but the locally-excited (LE) state of pyrene in Py-Bn-MoS2 efficiently generates an unusual emissive CTE state. Theoretical studies elucidate the interaction of MoS2 vacant orbitals with the pyrene LE state to form a CTE state that shows a distinct solvent dependence of the emission energy. This is the first example of organic-inorganic 2D hetero-nanostructures displaying mixed luminescence properties by an accurate design of the bridge structure, and therefore represents an important step in their applications for energy conversion and optoelectronic devices and sensors.
ABSTRACT
Graphene oxide (GO) with its unique two-dimensional structure offers an emerging platform for designing advanced gas separation membranes that allow for highly selective transport of hydrogen molecules. Nevertheless, further tuning of the interlayer spacing of GO laminates and its effect on membrane separation efficiency remains to be explored. Here, positively charged fullerene C60 derivatives are electrostatically bonded to the surface of GO sheets in order to manipulate the interlayer spacing between GO nanolaminates. The as-prepared GO-C60 membranes have a high H2 permeance of 3370 GPU (gas permeance units) and an H2/CO2 selectivity of 59. The gas separation selectivity is almost twice that of flat GO membranes because of the role of fullerene.
ABSTRACT
The stability of singly or multiply negatively charged π-conjugated organic compounds is greatly influenced by their electronic delocalization. Herein, we report a strategic methodology for isolation of a mysterious compound. The isolated compounds, a pyreno[4,5-b]pyrrole monoanion and pyreno[4,5-b:9,10-b']dipyrrole dianion, were highly stable under ambient conditions due to high delocalization of the negative charge over multiple electron deficient C[triple bond, length as m-dash]N groups and pyrene π-scaffolds and allowed purification by column chromatography. To our knowledge, this is the first report on TCNE type reductive condensation of malononitrile involving pyrene di- and tetraone and formation of pyrenopyrrole. All compounds were characterized by spectroscopic methods and X-ray crystallography. A UV-vis spectroscopic study shows an intense low energy absorption band with a large absorption coefficient (ε).
ABSTRACT
We synthesized thiophene-fused porphyrin dimers as effective π-extended helical chromophores. The porphyrin dimers exhibit a red-shifted absorption with the edge extending up to 1100 nm, implying strong electronic communication over the two porphyrin moieties through the thiophene-fused structure. Importantly, their racemic inversion barriers can be modulated by the central metal ions.
Subject(s)
Porphyrins/chemistry , Thiophenes/chemistry , Dimerization , Molecular StructureABSTRACT
Interfacial electron transfer across perovskite-electron acceptor heterojunctions plays a significant role in the power-conversion efficiency of perovskite solar cells. Thus, electron donor-acceptor thin films of halide perovskite nanocrystals receive considerable attention. Nevertheless, understanding and optimizing distance- and thickness-dependent electron transfer in perovskite-electron acceptor heterojunctions are important. We reveal the distance-dependent and diffusion-controlled interfacial electron transfer across donor-acceptor heterojunction films formed by formamidinium or cesium lead bromide (FAPbBr3/CsPbBr3) perovskite nanocrystals with TiO2/C60. Self-assembled nanocrystal films prepared from FAPbBr3 show a longer photoluminescence lifetime than a solution, showing a long-range carrier migration. The acceptors quench the photoluminescence intensity but not the lifetime in a solution, revealing a static electron transfer. Conversely, the electron transfer in the films changes from dynamic to static by moving toward the donor-acceptor interface. While radiative recombination dominates the electron transfer at 800 µm or farther, the acceptors scavenge the photogenerated carriers within 100 µm. This research highlights the significance of interfacial electron transfer in perovskite films.
ABSTRACT
For polycyclic aromatics with heterole-fused structures, the orientation of fused heterole rings as well as the geometry of their fused structures has a large impact on the physicochemical properties. In this study, a series of isomers of thiophene-fused naphthodiphospholes was designed and synthesized. Systematic investigation unveiled the explicit impact of heterole-fused structures on their structural and electronic properties. The isomers with 1,2/5,6-fused structure display phosphorescence due to enhanced spin-orbit coupling, whereas the isomers with 2,3/6,7-fused structure exhibit intense fluorescence. The trans isomers exhibited 1D slip π-stacked arrangement. In contrast, the cis isomers displayed 2D herringbone structure or columnar structure with a cavity. Therefore, the precisely controlled fusion of heterole rings is a universal approach to uncover their intrinsic properties for versatile applications as organic functional materials.
ABSTRACT
Morphological control of C60 fullerene using liquefied porphyrins (1 and 2) as the host matrices was explored. Slow evaporation of the solvent of the equimolar mixture of porphyrin and C60 in toluene afforded the porphyrin/C60 composite with a 3:1 molar ratio. The stoichiometric binding behaviors suggest that specific porphyrin-C60 interactions operate the formation of the porphyrin/C60 composites, as corroborated by spectroscopic and thermal properties, and glazing-incidence wide-angle X-ray diffraction. Under the bulk conditions, the conventional thermodynamic advantage of multiple binding cooperativity for molecular recognition is unlikely to explain the stoichiometric binding behaviors. Instead, we propose a size-matching effect on the porphyrin-C60 interaction in the bulk porphyrin matrices, i.e., "supramolecular solvation". The glassy nature of the porphyrin matrices was transmitted to C60 through the specific interaction, and the porphyrin/C60 composites adopted glassy states at room temperature.
ABSTRACT
Near-infrared (NIR) light control of living cellular activities is a highly desired technique for living cell manipulation because of its advantage of high penetrability towards living tissue. In this study, (π-extended porphyrin)-fullerene linked molecules are designed and synthesized to achieve NIR light control of the membrane potential. A donor-(π-extended porphyrin)-acceptor linked molecule exhibited the formation of the charge-separated state with a relatively long lifetime (0.68 µs) and a moderate quantum yield (27-31%). The hydrophilic trimethylammonium-linked triad molecule successfully altered PC12 cells' membrane potential via photoinduced intramolecular charge separation.
ABSTRACT
BACKGROUND/AIMS: Light-induced control of the cell membrane potential has enabled important advances in the study of biological processes involving the nervous system and muscle activity. The use of these light-induced modifications is expected in various medical applications, including the control of physiological responses and the recovery of lost functions by regulating nerve activity. In particular, charge-separating linkage molecules (Charge-Separation (CS) molecules) can depolarize cells by photoexcitation without genetic processing. However, the molecular mechanisms underlying cell membrane depolarization are unknown and have hindered its application. Here, we show that CS molecules localized in the cell membrane of PC12 cells using a high-density lipoprotein (HDL)-based drug carrier can excite the cells through a novel membrane current regulation mechanism by light irradiation. METHODS: Membrane potential, channel activity, and membrane capacitance were measured by patch clamp method in rat adrenal gland pheochromocytoma (PC12) cells and KV-overexpressing PC12 cells. CS molecules localized in the cell membrane of PC12 cells using HDL-based drug carrier. The localization of CS molecule was measured by a confocal microscopy. The mRNA expression was tested by RT-PCR. RESULTS: Current clamp measurements revealed that the photo-activated CS molecule causes a sharp depolarization of about 15 mV. Furthermore, it was shown by voltage clamp measurement that this mechanism inactivates the voltage-dependent potassium current and simultaneously generates photo-activated CS molecule induced (PACS) current owing to the loss of the cell membrane capacitance. This activity continues the depolarization of the target cell, but is reversible via a regenerative mechanism such as endocytosis and exocytosis because the cell membrane is intact. CONCLUSION: Thus, the mechanism of photo-induced depolarization concludes that photo-activated TC1 causes depolarization by generating PACS current in parallel with the suppression of the K+ current. Moreover, the depolarization slowly restores by internalization of TC1 from the membrane and insertion of new lipids into the cell membrane, resulting in the restoration of KV to normal activity and eliminating PACS currents, without cell damage. These results suggest the possibility of medical application that can safely control membrane excitation.
Subject(s)
Membrane Potentials/physiology , Photoreceptor Cells/metabolism , Animals , Cell Membrane/metabolism , Membrane Potentials/drug effects , PC12 Cells , Patch-Clamp Techniques/methods , Potassium/metabolism , Potassium Channel Blockers/pharmacology , Potassium Channels/metabolism , RatsABSTRACT
Phase-separated structures in photoactive layers composed of electron donors and acceptors in organic photovoltaics (OPVs) generally exert a profound impact on the device performance. In this study, nonfullerene acceptors (NFAs) where a heteronanographene central core was furnished with branched alkoxy chains of different lengths, TACIC-EH, TACIC-BO, and TACIC-HD, were prepared to adjust the aggregation tendency and systematically probe the relationships of film structures with photophysical and photovoltaic properties. The side-chain length showed negligible effects on the absorption properties and energy levels of TACICs. In addition, regardless of the chain length, all TACIC films exhibited characteristically long singlet exciton lifetimes (1330-2330 ps) compared to those in solution (≤220 ps). Using a conjugated polymer donor, PBDB-T, the best OPV performance was achieved with TACIC-BO that contained medium-length chains, exhibiting a power conversion efficiency (PCE) of 9.92%. TACIC-HD with the longest chains showed deteriorated electron mobility due to the long insulating alkoxy groups. Therefore, the PBDB-T:TACIC-HD-based device revealed a low charge collection efficiency and PCE (8.21%) relative to the PBDB-T:TACIC-BO-based device, but their film morphologies were analogous. Meanwhile, TACIC-EH with the shortest chains showed low solubility and formed micrometer-sized large aggregates in the blend film with PBDB-T. Although the charge collection efficiency of PBDB-T:TACIC-EH was lower than that of PBDB-T:TACIC-BO, the efficiencies of exciton diffusion to the donor-acceptor interface were sufficiently high (>98%) owing to the elongated singlet exciton lifetime of TACIC-EH. The PCE of the PBDB-T:TACIC-EH-based device remained moderate (7.10%). Therefore, TACICs with the long singlet exciton lifetimes in the films provide a clear guideline for NFAs with low sensitivity of OPV device performance to the blend film structures, which is advantageous for large-scale OPV production with high reproducibility.
ABSTRACT
Few-layered antimonene (FLSb) nanosheets were noncovalently functionalized with fullerene C60 clusters by quick addition of a poor solvent (i.e., acetonitrile) into a mixed dispersion of FLSb and C60 in a good solvent (i.e., toluene). In a flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurement, the FLSb-C60 composite, (FLSb+C60 )m , showed a rapid rise in transient conductivity, whereas no conductivity signal was observed in the single components, FLSb and C60 . This demonstrated the occurrence of photoinduced charge separation between FLSb and C60 in (FLSb+C60 )m . Furthermore, a photoelectrochemical device with an electrophoretically deposited (FLSb+C60 )m film exhibited an enhanced efficiency of photocurrent generation, compared to those of the single-components, FLSb and C60 , due to the photoinduced charge separation between FLSb and C60 . This work provides a promising approach for fabrication of antimonene-organic molecule composites and paves the way for their application in optoelectronics.
ABSTRACT
Porphyrins with a fused five-membered ring, such as 7,8-dehydropurpurins, have appeared as an emerging class of unique porphyrinoids. Their altered absorption spectra, relatively short lifetimes of excited states, and small HOMO-LUMO gaps arise from the harmony of the antiaromatic 20π-circuit and the aromatic 18π-circuit. In this regard, the electronic properties of 7,8-dehydropurpurins are expected to be controlled by modulating the contribution of the antiaromatic π-circuit to the whole aromaticity. Here the comparison of pyrrole- and phosphole-fused 7,8-dehydropurpurins is reported in terms of their aromaticity and physicochemical properties. The spectroscopic investigation revealed the larger contribution of the antiaromatic 24π-circuit in pyrrole-fused 7,8-dehyrdopurpurins than in phosphole-fused 7,8-dehydropurpurins. The DFT calculations also supported the feasibility of tuning the aromaticity of 7,8-dehydropurpurins by heterole-fused structures. Thus, the introduction of heterole-fused structures into porphyrinoids is a universal strategy to get new insight into aromaticity and their intrinsic properties in cyclic π-conjugated molecules.
ABSTRACT
Compositional engineering has been a strong tool to improve the quality of the perovskite materials and, in turn, the reproducibility of the solar cells. However, the control over the active layer uniformity, one of the most important requirements for the obtainment of efficient devices, is still a weak point of perovskite solar cells (PSCs) manufacturing. Here, we develop an approach to grow a uniform mixed cation perovskite layer, foreseeing its implementation in inverted solar cells endowing organic transporting layers, through the addition of a stoiochiometric amount of tropolone as chelating agent for the lead. Thanks to low melting and boiling temperatures, tropolone is present in the system only during the colloidal liquid phase, leaving the film during its formation; this unique characteristic promotes the obtainment of ideal perovskite surface morphologies and an increased short circuit current of photovoltaic devices. A maximum power conversion efficiency of 20% was obtained, with a 25% increase with respect to the reference.
ABSTRACT
Electron-acceptor small-molecules possessing a long exciton lifetime and a narrow energy band gap, opposing the energy gap law, are highly desirable for high-performance organic photovoltaics (OPVs) by realizing their efficient light-harvesting ability (LH), exciton diffusion (ED), and charge transfer (CT). Toward this goal, we designed an acceptor-donor-acceptor (A-D-A) type nonfullerene acceptor (NFA), TACIC, having an electron-donating, self-assembling two-dimensional (2D) nanographene unit, thienoazacoronene, at the center with electron-withdrawing groups at both ends. The TACIC film exhibited a narrow band gap (1.59 eV) with excellent LH. Surprisingly, the TACIC film showed an extremely long exciton lifetime (1.59 ns), suppressing undesirable nonradiative decay by its unique self-assembling behavior. When combined with a conjugated polymer donor, PBDB-T, slow ED and CT were observed (60 ps) with the excitation of TACIC owing to the large TACIC domain sizes. Nevertheless, the unusually high efficiencies of ED and CT (96% in total) were achieved by the long TACIC exciton lifetime. Additionally, unusual energy transfer (EnT) from the excited PBDB-T to TACIC was seen, demonstrating its dual LH role. The OPV device with PBDB-T and TACIC showed a high incident photon-to-current efficiency (IPCE) exceeding 70% at up to 710 nm and a power conversion efficiency of â¼10%. This result will open up avenues for a rational strategy of OPVs where LH, ED, and CT from the acceptor side as well as LH, EnT, ED, and CT from the donor side can be better designed by using 2D nanographene as a promising building block for high-performance A-D-A type NFAs.
ABSTRACT
In recent years, copper(I/II) complexes have emerged as alternative redox shuttles in dye-sensitized solar cells (DSSCs), exhibiting more positive redox potential than iodine- and cobalt-based redox shuttles. In particular, copper(I/II) complexes with 1,10-phenanthroline- or 2,2'-bipyridyl-based ligands attained moderate to high power conversion efficiencies (6-11%) with a high open-circuit voltage (VOC) over 1.0 V due to the positive potentials. Although copper(I/II) complexes with 1,10-phenanthroline-based ligands with 2,9-substituents have been developed, the effect of their ligand structures on the photovoltaic performance of DSSCs have not been fully addressed due to limited synthetic access to 1,10-phenanthroline derivatives. In this study, we designed and synthesized a series of copper(I/II) complexes with 1,10-phenanthroline ligands with different substituents at the 2,9-positions: bis(2-n-butyl-1,10-phenanthroline)copper(I/II) ([Cu(bp)2]1+/2+), bis(2-ethyl-9-methyl-1,10-phenanthroline)copper(I/II) ([Cu(emp)2]1+/2+), bis(2,9-diethyl-1,10-phenanthroline)copper(I/II) ([Cu(dep)2]1+/2+), and bis(2,9-diphenyl-1,10-phenanthroline)copper(I/II) ([Cu(dpp)2]1+/2+). The more positive redox potentials of [Cu(emp)2]1+/2+ and [Cu(dep)2]1+/2+, compared to that of bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) ([Cu(dmp)2]1+/2+), originate from the larger steric hindrance of the ethyl group instead of the methyl group, whereas the redox potential of [Cu(bp)2]1+/2+ is significantly shifted to the negative direction because of the lower steric hindrance of the 2-monosubstituted 1,10-phenanthroline ligands. The efficiency of the DSSC with [Cu(bp)2]1+/2+ (5.90%) is almost comparable to the DSSC with [Cu(dmp)2]1+/2+ (6.29%). In contrast, the DSSCs with [Cu(emp)2]1+/2+ (3.25%), [Cu(dep)2]1+/2+ (2.56%), and [Cu(dpp)2]1+/2+ (2.21%) exhibited lower efficiencies than those with [Cu(dmp)2]1+/2+ and [Cu(bp)2]1+/2+. The difference can be rationalized by the electron collection efficiencies. Considering the similar photovoltaic properties of the DSSCs with [Cu(bp)2]1+/2+ and [Cu(dmp)2]1+/2+, the use of copper(I/II) complexes with 2-monosubstituted 1,10-phenanthroline ligands as the redox shuttle may be useful to improve the short-circuit current density while retaining the rather high VOC value when dyes with a smaller bandgap (i.e., better light harvesting) are developed.
ABSTRACT
As structure defined cutouts of the graphene lattice, nanographene molecules have gained plenty of attention because of their high potential for versatile applications in organic electronics and energy conversion devices and as ideal model systems for the better understanding of intrinsic structure-property correlations of graphenes. In this study, well-defined nanographenes with sp2 carbon networks of different sizes, hexa-peri-hexabenzocoronene (HBC) and its rectangularly π-extended version, a short graphene nanoribbon (GNR), have been covalently functionalized with photoactive porphyrin molecules. On the basis of their spectroscopic studies, the photodynamics of the porphyrin-linked nanographenes was found to be influenced substantially by the size of the nanographenes. Photoexcitation of the porphyrin-HBC linked system led to exclusive energy transfer (EnT) from the first singlet excited state (S1) of the nanographene to the porphyrin, whereas opposite selective EnT occurred from the first and second singlet excited states (S1 and S2) of the porphyrin to the nanographene in the porphyrin-GNR linked system. In particular, ultrafast efficient EnTs from both the S2 and S1 states of the porphyrin to GNR mimic the corresponding ultrafast EnTs from the S2 and S1 states of carotenoids to chlorophylls in light-harvesting systems of natural photosynthesis. Such unique photophysical properties will be useful for the rational design of carbon-based photofunctional nanomaterials for optoelectronics and solar energy conversion devices.
ABSTRACT
Supramolecular composites composed of fullerene C60 and carbon nanodiamond (ND) were constructed through spontaneous complexation of C60 aggregates onto the surface of ND aggregates in N-methylpyrrolidone (NMP). The resulting C60 -ND composite was assembled onto a nanostructured SnO2 electrode by an electrophoretic deposition method. Formation of the C60 -ND composite was confirmed by dynamic light scattering (DLS) and field-emission scanning electron microscopy (FESEM). The C60 -ND composite on the SnO2 electrode showed high incident photon-to-current efficiencies (IPCEs) in the visible region as compared with the single component system of C60 or ND. The improved photocurrent generation of the C60 -ND composite may result from the photoinduced charge separation at the interface between C60 and ND. These results obtained here will provide valuable information on the design of optoelectronic devices based on all-nanocarbon materials.