We report a new triplet-triplet annihilation photon up-conversion (TTA-UC) system using an epitaxial Zn-perylene surface-supported metal-organic framework (SURMOF) grown on metal oxide surface as "emitter", and a platinum octaethylporphyrin (PtOEP) as "sensitizer" in [Co(bpy)(3)](2+/3+) acetonitrile solution. It has been demonstrated that the photocurrent can be significantly enhanced relative to epitaxial Zn-perylene SURMOF due to the TTA-UC mechanism. This initial result holds promising applications toward SURMOF-based solar energy conversion devices.
Metal-organic framework thin film-based dye sensitized solar cell is fabricated with highly oriented, crystalline, and porous Zn-perylene metal-organic framework (MOF) thin film (SURMOF) which is integrated with Bodipy embedded in poly(methyl methacrylate). It has been demonstrated that the photocurrent can be enhanced by a factor of 5 relative to Zn-perylene MOF thin film due to triplet-triplet annihilation up-conversion between the Bodipy/PMMA sensitizer and the Zn-perylene MOF thin film acceptor using Co(bpy)(3)(2+/3+) as redox mediator.
Three novel push-pull dyes, with carbazole donors, codedAJ502,TZ101andTZ102are synthesized and applied as co-sensitizers in dye-sensitized solar cells (DSSCs).TZ101andTZ102have similar structures except for two fluorine atoms introduced on the benzotriazole (BTZ) unit.AJ502shows a near-IR absorption spectrum that is suitable for co-sensitization withTZ101andTZ102. The co-sensitized DSSC device based onCO-1(AJ502 : TZ101= 3 : 4 (0.075 mM : 0.1 mM)) achieves a power conversion efficiency (PCE) of 10.3% under AM 1.5G irradiation, with 1.06 V open-circuit voltage (Voc), 13.75 mA cm−2short-circuit photocurrent density (Jsc), and 70.8% fill factor (FF), a significant improvement compared to the single dye, 6.0% forAJ502and 5.1% forTZ101with a copper(i/ii)-based redox electrolyte. A PCE of 8.9% is also obtained by devices based onCO-2(AJ502 : TZ102= 3 : 4). ForCO-1, the fluorine atoms inTZ101play a critical role by widening the active light capturing bands of bothTZ101andAJ502on the TiO2film whileTZ102andAJ502show weaker interaction under the same conditions. The UV-vis spectrum and Raman spectrum revealed thatAJ502can form supramolecules withTZ101andTZ102formed on the TiO2film.
Colloidal quantum dot (CQD) solar cells with a ZnO/PbS-TBAI/PbS-EDT/carbon structure were prepared using a solution processing technique. A commercially available carbon paste that was processed at low-temperatures was used as a counter electrode in place of expensive noble metals, such as Au or Ag, which are used in traditional PbS CQD solar cells. These CQD solar cells exhibited remarkable photovoltaic performance with a short circuit density (Jsc) of 25.6 mA/cm2, an open circuit voltage (Voc) of 0.45 V, a fill factor (FF) of 51.8% and a power conversion efficiency (PCE) as high as 5.9%. A reference device with an Au counter electrode had a PCE of 6.0%. The PCE of the carbon-containing CQD solar cell remained stable for 180 days when tested in ambient atmosphere, while the PCE of the Au-containing CQD solar cell lost 48.3% of its original value. Electrochemical impedance spectroscopy (EIS) demonstrated that holes within the PbS CQD were effectively transported to the carbon counter electrode.
Three novel dyes consisting of a 5,8,15-tris(2-ethylhexyl)-8,15-dihydro-5H-benzo[1,2-b:3,4-b':6,5-b″]tricarbazole (BTC) electron-donating group and a 4,7-bis(4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (BTBT) π-bridge with an anchoring group of phenyl carboxyl acid were synthesized and applied in dye-sensitized solar cells (DSCs).The AJ202 did not contain any triple bonds, the AJ201's ethynyl group was inserted between the BTC and BTBT units, and the AJ206's ethynyl group was introduced between the BTBT moiety and the anchor group. The inclusion and position of the ethynyl linkage in the sensitizer molecules significantly altered the electrochemical properties of these dyes, which can fine-tune the energy levels of the dyes. The best performing devices contained AJ206 as a sensitizer and a Cu(I/II) redox couple, which resulted in a power conversion efficiency (PCE) up to 10.8% under the standard AM 1.5 G illumination, which obtained PCEs higher than those from the devices that contained AJ201 (9.2%) and AJ202 (9.7%) under the same conditions. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the sensitizers were tuned to be well-suited for the Cu(I/II) redox potential and the Fermi level of TiO2. The innovative synthesis of a tricarbazole-based donor moiety in a sensitizer used in combination with a Cu(I/II) redox couple has resulted in relatively high PCEs.
Two novel dyes that are similar in chemical structure, except for different donor units, AJ301and AJ303 were synthesized, characterized and applied as sensitizers in dye-sensitized solar cells (DSSCs). Both dyes exhibited a wide absorption of visible sunlight. The introduction of fused rings on the donor unit of AJ303 presented an appropriate energy level, less recombination and longer electron lifetime to achieve a power conversion efficiency (PCE) of 10.2%, far above that achieved for AJ301 of 6.2% with a [Co(bpy)(3)](2+/3+)-based electrolyte under standard AM1.5G solar irradiation (100 mW cm(-2)). The DSSCs based on AJ303 and AJ301 with [Cu(tmby)(2)](2+/+)-based electrolyte showed a lower PCE of 8.2% and 5.4%, respectively. Therefore, the results indicated that the introduction of a fused-ring in the donor group is a meaningful synthetic strategy to improve the photovoltaic performance.
Two series of mononuclear ruthenium complexes [Ru(pdc)L-3] (H(2)pdc = 2,6-pyridinedicarboxylic acid; L = 4-methoxypyridine, 1; pyridine, 2; pyrazine, 3) and [Ru(pdc)L-2(dmso)] (dmso = dimethyl sulfoxide; L = 4-methoxypyridine, 4; pyridine, 5) were synthesized and spectroscopically characterized. Their catalytic activity toward water oxidation has been examined using Ce-IV (Ce(NH4)(2)(NO3)(6)) as the chemical oxidant under acidic conditions. Complexes 1, 2 and 3 are capable of catalyzing Ce-IV-driven water oxidation while 4 and 5 are not active. Electronic effects on their catalytic activity were illustrated: electron donating groups increase the catalytic activity.
A new mu-phenoxy-mu-metoxy di-manganese(III) complex with the trisphenolic ligand, 2,6-bis[((2-hydroxybenzyl)(2-pyridylmethyl)amino)methyl]-4-methylphenol, was isolated as a perchlorate salt. The X-ray structure shows that the two manganese(III) ions are in a distorted octrahedral enviroment with approximately perpendicular Jahn-Teller axes. Investigation of the molar magnetic susceptibility reveals a ferromagnetic coupling between the two high-spin manganese(III) ions. Fitting of the data led to g = 2 and J = 12.5 cm(-1).
Three CB[8]s have been reversibly locked between two Ru(bpy)(3)-viologen complexes by light driven electron transfer reactions.
The binding interactions between cucurbit[8]uril (CB[8]) and a dicationic guest N,N-dimethyl-3,3'-dimethyl-4,4'-bipyridinium (DMV2+) have been investigated by various experimental techniques including NMR, ESI-MS, and UV/Vis and fluorescence spectroscopy. In a three-component system consisting of CB[81, N,N-dimethyl-4,4'-bipyridinium (MV2+) and DMV2+, CB[8] was found to exhibit a higher binding affinity to DMV2+ than to MV2+, When DMV2+ was connected to MV2+ by an alkyl chain, the first equiv. of CB[8] could be selectively positioned on the DMV2+ moiety, and then a second equiv. of CB[8] was positioned on the MV2+ moiety. Spectroelectrochemical studies showed that upon the reduction of this system at -0.6 V vs. AgCl, the CB[8] could move from the DMV2+ moiety to the MV+center dot radical, which formed a dimer inside the CB[8] cavity. Molecular oxygen quenched the dimer, and the CB[8] moved back to the DMV2+ moiety, indicating it molecular movement driven by electrochemistry. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Molecular ruthenium catalysts were found to selectively catalyze the oxidation of thioanisole to sulfoxide with a yield up to 100% in the presence of visible light and sacrificial reagents when they were anchored onto hematite powder. The composite photocatalysts also showed about 5 times higher efficiencies in benzyl alcohol oxidation than the system composed of dispersed molecular catalysts and hematite particles in aqueous solution. A photoelectrochemical cell based on a molecular catalyst modified hematite photoanode was further fabricated, which exhibited high activity towards the oxidation of organic substrates.
To celebrate the 10 year anniversary of ChemSusChem, we as the chairmen of the editorial board are writing this Essay to summarize important scientific contributions to our journal during the past decade in terms of sustainable science and technology. Bibliometric analysis of published papers show that biorefinery, solar energy conversion, energy-storage materials, and carbon dioxide utilizations attracted most attention in this area. According to our own knowledge and understanding and from the sustainability point of view, we are also pointing out those research directions that we believe can play key roles in the future chemistry to meet the grand challenges in energy and environment. Hopefully, these perspective aspects will provide the readers with new angles to look at the chemistry in the coming decades and inspire the development of new technologies to make our society sustainable.
The exploration of alternative molecular hole-transporting materials (HTMs) specifically for high performance perovskite solar cells (PSCs) is a relatively recent research area. Aiming for further increasing the 'efficiency-cost ratio' of PSCs, we developed a spiro[fluorene-9,9'-xanthene] based HTM (X59) via two-step synthesis from commercial precursors for perovskite solar cells (PSCs) that works as effectively as the well-known HTM-Spiro-OMeTAD-based device under the same conditions. The molecular structure was analyzed by X-ray crystallography indicating a similar packing regime as for Spiro-OMeTAD. An impressive PCE of 19.8% was achieved by using X59 as HTM in PSC, which can compete with the record PCE of 20.8% by using the state-of-the-art-HTM Spiro-OMeTAD (Tress et al., 2016) [1]. The optimized devices employing X59 as HTM exhibited minimized hysteresis, excellent reproducibility and reasonable stability under dark and dry conditions. The present finding highlights the potential of spiro-type HTM for high performance PSCs and paves the way to a much deceased fabrication cost for potential commercialization of perovskite solar panels.
Four unsymmetric dinuclear ruthenium and osmium complexes, Os(bpy)(3)-viologen-Ru(bpy)(3) (1; bpy= 2,2'-bipyridyl), Ru(bpy)(3)-viologen-Ru(bpy)(dcbpy)(2) (2; dcbpy= 4,4'-dicarboxy1-2,2-bipyridyl), Os(bpy)(3)-viologen-Ru(bpy)(dcbpy)(2) (3) and rotaxane 1 subset of CB[7] (CB[7] = cucurbit[7]uril), were successfully synthesized. The NMR, electrochemistry and photochemistry studies of these complexes were performed in non-aqueous solutions. The results show that the CB[7] host mainly locates at the butyl linker part of the osmium side in an acetonitrile solution. This binding lowers the oxidation potential of osmium whereas the oxidation potential of ruthenium does not change. The oxidation potential of ruthenium in complexes 2 and 3 is higher due to the electron withdrawing property of carboxylic anchor groups. Analysis with UV-vis spectra shows the viologen radical formation and reversed process of these complexes in non-aqueous solutions.
A small organic sensitizer, the polyene-diphenylaniline dye D5, was compared with the standard sensitizer N719 (Ru(dcbPY)(2)(NCS)(2)) in a dyesensitized solar cell investigation. In solar cells with relatively thin layers of mesoporous TiO2 (< 3 mu m) D5 outperformed N719 because of its high extinction coefficient. D5 showed also better performance than N719 in the case of sensitization of mesoporous ZnO. In solid-state solar cells, where the iodide/triiodide electrolyte was replaced by an amorphous hole conductor (spiro-OMeTAD), D5 gave promising preliminary results. The hole conductivity, observed in monolayers of D5 adsorbed at TiO2, may possibly lead to improved performance in such cells.
The development of facilely synthesized, dopant-free hole-transporting materials (HTMs) with high efficiency is of great significance for the potential application of perovskite solar cells (PSCs). Herein, we report two novel indolo[3,2-b]carbazole (ICZ) based small molecules obtained via a three-step reaction in a high yield without using expensive catalysts, namely C201 and C202, and further apply them as dopant-free HTMs in PSCs. Compared with C201, C202 contains two additional biphenylamino groups to improve its spatial configuration. It is found that the interplay between the molecular geometry and the aggregation behavior can exert a great influence on the film formation property and thus on the device performance. Strikingly, the champion devices employing C202 as the HTM deliver a much higher PCE of up to 17.7%, which is substantially higher than that of devices containing C201 (8.7%) under 100 mW cm(-2) illumination (AM 1.5G). It is revealed that the C202 capping layer exhibits a more homogeneous and uniform surface morphology as compared to that of C201, which effectively reduces the charge recombination losses and facilitates charge extraction, leading to a much-enhanced photovoltaic performance. This is the first example of ICZ core-based small molecules as dopant-free HTMs in PSCs. Moreover, the PSCs containing C202 as the HTM also exhibited good long-term stability under ambient conditions (40% RH) as compared to devices with doped spiro-OMeTAD, due largely to the hydrophobic nature of C202 which prevented moisture from destroying the perovskite film. This work offers a new avenue for developing cost-effective and stable HTMs for PSCs and other optoelectronic devices.
Two novel fluorene-based hole transporting materials (HTMs) were synthesized to be used in perovskite solar cells (PSCs). C102 was designed based on C101 by simply linking the two carbon-carbon single bonds to compose a "dispiro" structure. Their typically similar structures cause them sharing almost the same energy levels. However, their photovoltaic performances are quite different due to the small variations. The PSC that contained the "dispiro" structure, C102, reached a power conversion efficiency (PCE) of 17.4%, while the device contained C101, obtained a lower PCE of 15.5%. Electrochemical properties and Photovoltaic characterization of the two materials have been investigated to explain the result. It is shown that C102 has a stronger ability to transport holes and resist the charge recombination. Thus, the dispiro structure should be more appropriate being used as HTM in PSCs. Physics, Chinese Academy of Sciences.
Pure inorganic perovskite of CsPbI3 attracts great attentions due to its excellent thermal stability and more suitable bandgap for tandem solar cells. The power conversion efficiency (PCE) of CsPbI3 perovskite solar cells has swiftly increased to 19.03%. However, extensive researches on the material property and photovoltaic characterization are rather rare in the literatures. In this study, a remarkable light soaking effect is found in the CsPbI3 based perovskite solar cells as the PCE increases from 10.8% to 18.3% after 180 s soaking under AM 1.5G sunlight. Mechanisms behind this reproducible soaking effect have also been studied. It reveals that the depressed dark current caused by a stronger built-in field and the decreased defects density passivated by the photogenerated electrons result in the enhanced PCE after light soaking. Moreover, we carefully characterize that the supposed "HPbI3" should be "DMAPbI(3)" synthesized through anti-solvent vapor recrystallisation method.
The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium-cobalt dyads, which belong to the large family of donor-bridge-acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray
Direct photo-electrochemical (PEC) water splitting is of great practical interest for developing a sustainable energy systems, but remains a big challenge owing to sluggish charge separation, low efficiency, and poor stability. Herein, a 3D porous In2O3/In2S3 pyramid heterostructure array on a fluorine-doped tin oxide substrate is fabricated by an ion exchange–induced synthesis strategy. Based on the synergistic structural and electronic modulations from density functional theory calculations and experimental observations, 3D porous In2O3/In2S3 photoanode by the protective layer delivers a low onset potential of ≈0.02 V versus reversible hydrogen electrode (RHE), the highest photocurrent density of 8.2 mA cm−2 at 1.23 V versus RHE among all the In2S3 photoanodes reported to date, an incident photon-to-current efficiency of 76% at 400 nm, and high stability over 20 h for PEC water splitting are reported. This work provides an alternative promising prototype for the design and construction of novel heterostructures in robust PEC water splitting applications.
All-inorganic CsPbIBr2 perovskite has attracted widespread attention in photovoltaic and other optoelectronic devices because of its superior thermal stability. However, the deposition of high-quality solution-processed CsPbIBr2 perovskite films with large thicknesses remains challenging. Here, we develop a triple-component precursor (TCP) by employing lead bromide, lead iodide, and cesium bromide, to replace the most commonly used double-component precursor (DCP) consisting of lead bromide and cesium iodide. Remarkably, the TCP system significantly increases the solution concentration to 1.3 M, leading to a larger film thickness (∼390 nm) and enhanced light absorption. The resultant CsPbIBr2 films were evaluated in planar n-i-p structured solar cells, which exhibit a considerably higher optimal photocurrent density of 11.50 mA cm−2 in comparison to that of DCP-based devices (10.69 mA cm−2). By adopting an organic surface passivator, the maximum device efficiency using TCP is further boosted to a record efficiency of 12.8% for CsPbIBr2 perovskite solar cells.
The main of this work is to overcome the drawbacks of the traditional fullerene derivatives used as electron transport materials (ETMs) for perovskite solar cells (PSCs). Herein, a new strategy to design non-fullerene ETMs is presented by molecular engineering to include charged moieties in the ETM. The designed ETM FA2+-PDI2 is intrinsically ionic and the incorporated counter ions in FA2+-PDI2 significantly increase the electron conductivity and improve the film formation properties. Through careful device optimization, PSCs based on the ionic ETM FA2+-PDI2 exhibit an impressive average power conversion efficiency (PCE) of 17.0%, which is comparable to the PSC based on PC61BM (17.5%). The superior photovoltaic performance can be attributed to efficient electron extraction and effective electron transfer in the PSCs. This work provides important insights regarding the future design of new and efficient non-fullerene ETMs for PSCs.
Layered nickel-iron oxide/hydroxide nanosheets have proven to be the most efficient catalyst for the water oxidation reaction. Introducing structural defects to the nanosheets is a particularly attractive method for increasing the number of active sites and tailoring the intrinsic electronic properties. Herein, defects were introduced on Ni−Fe nanosheets through sequentially electrodoping and dedoping the surface of the material with tetramethylammonium ions. The as-prepared defect-rich Ni−Fe nanosheets showed an enhanced catalytic performance for the oxygen evolution reaction (OER) compared with conventional NiFe layered double hydroxides (LDHs), exhibiting an overpotential of only 172 mV at the current density of 10 mA cm−2. The relationship between pH and OER activity indicated that the lattice oxygens participated in the catalytic OER process as active sites. This work provides new insights into the understanding of the structure-activity relationship of layered materials and helps to develop new methods to implement defects on such frameworks aided by organic molecules.
In this work, we have designed and synthesized a novel molecular material, BDT-C1, in which the core unit, benzodithiophene (BDT), was functionalized by thiophene (TP) and benzo-[c][1,2,5]-thiadiazole (BTZ) derivatives to generate extended pi-conjugation. BDT-C1 shows high hole mobility and high conductivity in its pristine form, in combination with appropriate energy level alignment with respect to [CH3NH3]PbI3 and PC70BM, qualifying the material as a good candidate for application both in perovskite solar cells (PSCs) as dopant-free hole transport material (HTM) and in OSCs as donor material. The champion PSCs based on BDT-C1 show an average conversion efficiency (PCE) of 13.4% (scan forward: 13.9%; scan backward: PCE=12.9%, scan rate: 10 mV/s). Although the average efficiency obtained is slightly lower than that of reference devices based on the well-known doped HTM Spiro-OMeTAD (13.7%), the BDT-C1 based devices exhibit better stability. Moreover, BDT-C1 as a donor material in OSCs also shows good performance in combination with PC70BM as acceptor material, and an efficiency of 6.1% was obtained. The present results demonstrate that BDT-C1 works well as both donor material in OSCs as well as dopant-free HTMs for efficient PSCs.
There has been a growing interest in the design and synthesis of non-fullerene electron transport materials (ETMs) for perovskite solar cells (PSCs), which may overcome the drawbacks of traditional fullerene derivatives. In this work, a novel donor-acceptor (D-A) structured ETM termed TPA-3CN is presented by molecular engineering of triphenylamine (TPA) as the donor group and (3-cyano-4,5,5-trimethyl-2(5H)-furanylidene) malononitrile as the acceptor group. To further improve the electron mobility and conductivity and achieve excellent photovoltaic performance, a solution processable n-type dopant is introduced during the ETM spin-coating step. After device optimization, PSCs based on the doped TPA-3CN exhibit an impressive power conversion efficiency (PCE) of 19.2% with a negligible hysteresis. Benefitting from the low temperature and good solution processability of ETM TPA-3CN, it was further applied in flexible inverted PSCs and an impressive PCE of 13.2% was achieved, which is among the highest values reported for inverted flexible fullerene-free PSCs.
Organic dyes have become widely used in dye-sensitized solar cells (DSSCs) because of their good performance, flexible structural modifications, and low costs. To increase the photostability of organic dye-based DSSCs, we conducted a full study on the degradation mechanism of cyanoacrylic acid-based organic sensitizers in DSSCs. The results showed that with the synergy between water and UV light, the sensitizer could desorb from the TiO2 surface and the cyanoacrylic acid unit of the sensitizer was transformed into the aldehyde group. It was also observed that the water content had a great effect on the degradation process. Our experiments conducted using O-18-labeled water demonstrated that the oxygen atom of the aldehyde group identified in the degraded dye came from the solvent water in the DSSCs. Therefore, controlling the water content during DSSC fabrication, good sealing of cells, and filtering the UV light are crucial to produce DSSCs that are more durable and robust.
Novel organic dyes CC201 and CC202 with dihydrothiazole derivative as pi-bridge have been synthesizedand applied in the DSSCs. With the synergy electron-withdrawing of dihydrothiazole and cyanoacrylic acid, these two novel dyes CC201 and CC202 show excellent response in the region of 500-800 nm. An efficiency as high as 6.1% was obtained for the device fabricated by sensitizer CC202 together with cobalt electrolyte under standard light illumination (AM 1.5G, 100 mW cm(-2)). These two novel D-pi-A panchromatic organic dyes gave relatively high efficiencies except common reported squaraine dyes.
A series of novel organic dyes containing a benzopyran ring as a p-bridge have been designed and applied in dye-sensitized solar cells (DSSCs). This series of dyes show the excellent DSSCs' performance, due to their efficient light-to-photocurrent conversion in the region from 380 nm to 600 nm, with the highest IPCE values exceeding 90%. Through modification of the donor units, an efficiency as high as 7.5% has been achieved under standard light illumination (AM 1.5G, 100 mW cm(-2)) by the dye CC103.
Water splitting is deemed as an effective pathway for producing ideal clean energy, such as hydrogen. Here, a copper oxide film (Cu-Tris film) was prepared in-situ from a 0.2 M phosphate buffer solution (pH = 12.0) containing 1.0 mM Cu2+ and 2.0 mM Tris via controlled-potential electrodeposition. The Cu-Tris film showed a significantly low overpotential of 390 mV at a current density of 1.0 mA/cm2 for electrocatalytic water oxidation. Simultaneously, a considerably low Tafel slope of 41 mV/decade was achieved. This Cu-Tris film also exhibited a high and stable current density of ca. 7.5 mA/cm2 at 1.15 V vs. NHE for long-term electrocatalysis (10 h). These results demonstrated the superior performance of the developed Cu-Tris film, which should be attributed to the regulating effect of the five coordinated planar structure of the Cu-Tris complex precursor during the process of electrodeposition.
Many nonprecious metal-selenide-based materials have been reported as electrocatalysts with high activity for the oxygen evolution reaction (OER). Herein, a hybrid catalyst film composed of Cu2Se and Cu2O nanoparticles directly grown on Ti foil (Cu2Se-Cu2O/TF) was prepared through a simple and fast cathodic electrodeposition method. Surprisingly, this electrode required a relatively low overpotential of 465 mV to achieve a catalytic current density of 10 mA cm-2 for the OER in 0.2 M carbonate buffer (pH = 11.0). Furthermore, a long-term constant current electrolysis test confirmed the high durability of the Cu2Se-Cu2O/TF anode at a current density of 10 mA cm-2 over 20 h. The XRD, TEM and XPS analysis of the sample after the OER indicated that a CuO protective layer formed on the surface of the Cu2Se-Cu2O catalyst, which effectively suppressed further oxidation of the Cu2Se-Cu2O catalyst during the OER and resulted in sustained catalytic oxidation of water.
A cobalt-based film (Co-Hi) for water oxidation was prepared in 2-[4-(2-hydroxyethyl) piperazin-1-yl]ethanesulfonic acid buffer at pH 7.0 through a unique cyclic voltammetry electrodeposition method by applying a wide scan range from 1.40 to -1.00 V versus normal hydrogen electrode (NHE). This catalyst film displayed highly efficient activity during oxygen evolution in neutral aqueous solution. An impressive current density of more than 1.5 mAcm(-2) that was stable over a prolonged time period was obtained with a remarkably low onset overpotential of 230 mV in 0.1 M phosphate buffer (pH 7.0).
Water splitting is of paramount importance for exploiting renewable energy-conversion and -storage systems, but is greatly hindered by the kinetically sluggish oxygen evolution reaction (OER). In this work, a three-dimensional, highly efficient, and durable NiFe/Cu2O nanowires/Cu foam anode (NiFe/Cu2O NWs/CF) for water oxidation in 1.0m KOH was developed. The obtained electrode exhibited a current density of 10mAcm(-2) at a uniquely low overpotential of =215mV. The average specific current density (j(s)) was estimated, on the basis of the electrocatalytically active surface area, to be 0.163mAcm(-2) at =310mV. The electrode also displayed a low Tafel slope of 42mVdecade(-1). Moreover, the NiFe/Cu2O NWs/CF electrode could maintain a steady current density of 100mAcm(-2) for 50h at an overpotential of =260mV. The outstanding electrochemical performance of the electrode for the OER was attributed to the high conductivity of the Cu foam and the specific structure of the electrode with a large interfacial area.
[FeFe] hydrogenase mimics: Two polynuclear iron-sulfur complexes (1 and 2; see figure) were prepared and structurally characterized. They are potentially effective and stable multielectron-transfer relays for mediating four- and six-electron transformations via a cascade of reversible two-electron redox steps with relatively narrow potential spans.
Two tetranuclear iron-sulfur complexes, (mu,mu-pbtt)[Fe-2(CO)(6)](2) (pbtt = benzene-1,2,4,5-tetrathiolato, 3) and (mu,mu-obtt)[Fe-2(CO)(6)](2) (obtt = benzene-1,2,3,4-tetrathiolato, 4), were prepared from reaction of Fe-3(CO)(12) and the corresponding tetramercaptobenzene in THF, respectively. Complexes 5 and 6, (mu,mu-pbtt)[Fe-2(CO)(5)L-1][Fe-2(CO)(5)L-2] (L-1 = CO, L-2 = PPyr(3) (Pyr = N-pyrrolyl), 5; L-1 = L-2 = PPyr(3), 6) were obtained by controlling CO displacement of 3 with PPyr(3). Molecular structures of 3-6 were determined by spectroscopic and single-crystal X-ray analyses. All-CO Fe4S4 complexes 3 and 4 each display four-electron reduction processes in consecutive chemically reversible two-electron reduction events with relatively narrow potential spans in the cyclic voltammograms. Phosphine-substituted Fe4S4 complexes 5 and 6 exhibit two consecutive two-electron reduction events, which are not fully reversible. The electrocatalytic properties of 3 and 4 for proton reduction were studied using a series of carboxylic acids of increasing strength (CH3COOH, CH2ClCOOH, CHCl2COOH, CCl3COOH, and CF3COOH). The mechanisms for electrochemical proton reduction to hydrogen catalyzed by complex 3 as a function of acid strength are discussed.
Self-assembled molecular iron and cobalt catalysts (MP4N2, M = Fe, Co) bearing a multihydroxy-functionalized tetraphosphine ligand electrocatalyze H-2 generation from neutral water on a mercury electrode at -1.03 and -0.50 V vs. NHE, respectively. Complex CoP4N2 displays extremely low overpotential (E-onset = 80 mV) while maintaining high activity and good stability. Bulk electrolysis of CoP4N2 in a neutral phosphate buffer solution at -1.0 V vs. NHE produced 9.24 x 10(4) mol H-2 per mol cat. over 20 h, with a Faradaic efficiency close to 100% and without apparent deactivation.
Novel organic dyes (C1-1, C1-5 and C2-1) with a tetrahydroquinoline moiety as the electron donor, different thiophene-containing electron spacers and a cyanoacrylic acid moiety as the electron acceptor have been designed and synthesized for the application in dye-sensitized solar cells (DSSCs). An interesting relationship between the dye structures, properties, and the performance of DSSCs based on these tetrahydroquinoline dyes is obtained. Although C2-1 dye, which has a rigid electron spacer, has the narrowest action spectrum among these dyes, it gives the highest solar-to-electricity conversion efficiency (eta) of 4.49% (V-oc = 600 mV, J(sc) = 11.20 mA/cm(2), ff = 0.67) of a DSSC under simulated AM 1.5 irradiation (100 mW/cm(2)). Under the same conditions, the eta value of a DSSC based on N3 dye is 6.16%.
Eleven novel donor acceptor pi-conjugated (D-pi-A) organic dyes have been engineered and synthesized as sensitizers for the application in dye-sensitized solar cells (DSSCs). The electron-donating moieties are substituted tetrahydroquinoline, and the electron-withdrawing parts are cyanoacrylic acid group or cyanovinylphosphonic acid group. Different lengths of thiophene-containing conjugation moieties (thienyl, thienylvinyl, and dithieno[3,2-b;2',3'-d]thienyl) are introduced to the molecules and serve as electron spacers. Detailed investigation on the relationship between the dye structure, photophysical and photoelectrochemical properties, and performance of DSSCs is described here. The bathochromic shift and increase of the molar extinction coefficient of the absorption spectrum are achieved by introduction of larger conjugation moiety. Even small structural changes of dyes result in significant changes in redox energies and adsorption manner of the dyes on TiO2 surface, affecting dramatically the performance of DSSCs based on these dyes. The higher performances are obtained by DSSCs based on the rigid dye molecules, C2 series dyes (Figure 1), although these dyes have lower light absorption abilities relative to other dyes. A maximum solar-to-electrical energy conversion efficiency (eta) of 4.53% is achieved under simulated AM 1.5 irradiation (100 mW/cm(2)) with a DSSC based on C2-2 dye (V-oc = 597 mV, J(sc) = 12.00 mA/cm(2), ff = 0.63). Density functional theory (DFT) calculations have been performed on the dyes, and the results show that electron distribution from the whole molecules to the anchoring moieties occurred during the HOMO-LUMO excitation. The cyanoacrylic acid groups or cyanovinylphosphonic acid group are essentially coplanar with respect to the thiophene units, reflecting the strong conjugation across the thiophene-anchoring groups.
Novel thiophene-pi-conjugated donor-acceptor molecules, 5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-vinyl]-thioph ene2-carbaldehyde (QTC) and (1-cyano-2-{5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-v inyl]-thiophen-2-yl}-vinyl)-phosphonic acid diethyl ester (QTCP), were designed and synthesized. Combined experimental and theoretical methods were performed to investigate the photoinduced intramolecular charge-transfer (ICT) processes of these compounds. Steady-state absorption and fluorescence measurements in different solvents indicate the photoinduced ICT characters of QTC and QTCP. Solvent dependency of the large Stokes shifts and high dipole moment of the excited state also support the charge-transfer character of the excited state. Theoretical calculations based on time-dependent density functional theory (TDDFT) method were performed to investigate ICT states of these compounds. The results reveal that the excited states have adopted a distortion of the C=C double bond between the donor moiety and the thiophene-pi-bridge.
Novel cyanine dyes, in which a tetrahydroquinoline derivative is used as an electron donor and 1-butyl-5-carboxy-3, 3-dimethyl-indol-1-ium moiety is used as an electron acceptor and anchoring group, were designed and synthesized for application in dye-sensitized solar cells. The photovoltaic performance of these solar cells depends markedly on the molecular structure of the dyes in terms of the n-hexyl chains and the methoxyl unit. Retardation of charge recombination caused by the introduction of n-hexyl chains resulted in an increase in electron lifetime. As a consequence, an improvement of open-circuit photovoltage (V oc) was achieved. Also, the electron injection efficiencies were improved by the introduction of methoxyl moiety, which led to a higher short-circuit photocurrent density (Jsc). The highest average efficiency of the sensitized devices (η) was 5.6 % (Jsc=13.3 mA cm-2, Voc=606 mV, and fill factor FF=69.1 %) under 100 mW cm-2 (AM 1.5G) solar irradiation. All of these dyes have very high absorption extinction coefficients and strong absorption in a relatively narrow spectrum range (500-650 nm), so one of our organic dyes was explored as a sensitizer in co-sensitized solar cells in combination with the other two other existing organic dyes. Interestingly, a considerably improved photovoltaic performance of 8.2 % (Jsc=20.1 mA cm-2, Voc=597 mV, and FF=68.3 %) was achieved and the device showed a panchromatic response with a high incident photon-to-current conversion efficiency exceeding 85 % in the range of 400-700 nm. Sensitive dyes absorb it all: Co-sensitization of three spectrally complementary dyes on a TiO2 film in a well-designed sequence significantly improves the photovoltaic performance of the device, and an efficiency of 8.2 % is achieved. The devices demonstrate a panchromatic response with an incident photon-to-current conversion efficiency >80 % over the entire visible spectral region from 400 to 700 nm.
Perovskite solar cells (PSCs) have attracted significant interest and hole transporting materials (HTMs) play important roles in achieving high efficiency. Here, we report additive free ionic type HTMs that are based on 2-ethylhexyloxy substituted benzodithiophene (BDT) core unit. With the ionization of end-capping pyridine units, the hole mobility and conductivity of molecular materials are greatly improved. Applied in PSCs, ionic molecular material M7-TFSI exhibits the highest efficiency of 17.4% in the absence of additives [lithium bis(trifluor-omethanesulfonyl)imide and 4-tert-butylpyridine]. The high efficiency is attributed to a deep highest occupied molecular orbital (HOMO) energy level, high hole mobility and high conductivity of M7-TFSI. Moreover, due to the higher hydrophobicity of M7-TFSI, the corresponding PSCs showed better stability than that of Spiro-OMeTAD based ones. In addition, the strong absorption and suitable energy levels of materials (M6, M7-13r and M7-TFSI) also qualify them as donor materials in organic solar cells (OSCs) and the devices containing M7-TFSI as donor material displayed an efficiency of 6.9%.
We demonstrate a high efficiency perovskite solar cell (PSC) integrated with a bulk heterojunction layer, based on acceptor-donor-acceptor (A-D-A) type hole transport material (HTM) and PC70BM composite, yielding improved photoresponse. Two A-D-A-structured hole transporting materials termed M3 and M4 were designed and synthesized. Applied as HTMs in PSCs, power conversion efficiencies (PCEs) of 14.8% and 12.3% were obtained with M3 and M4, respectively. The HTMs M3 and M4 show competitive absorption, but do not contribute to photocurrent, resulting in low current density. This issue was solved by mixing the HTMs with PC70BM to form a bulk heterojunction (BHJ) layer and integrating this layer into the PSC as hole transport layer (HTL). Through careful interface optimization, the (FAPbI(3))(0.85)(MAPbBr(3))(0.15)/HTM:PC70BM integrated devices showed improved efficiencies of 16.2% and 15.0%, respectively. More importantly, the incident-photon-to-current conversion efficiency (IPCE) spectrum shows that the photoresponse is extended to 900 nm by integrating the M4:PC70BM based BHJ and (FAPbI(3))(0.85)(MAPbBr(3))(0.15) layers.
Based on the previous research work in our laboratory, we have designed and synthesized a small-molecule, hole transport material (HTM) POZ6-2 using phenoxazine (POZ) as central unit and dicyanovinyl units as electron-withdrawing terminal groups. Through the introduction of a 2-ethyl-hexyl bulky chain into the POZ core unit, POZ6-2 exhibits good solubility in organic solvents. In addition, POZ6-2 possesses appropriate energy levels in combination with a high hole mobility and conductivity in its pristine form. Therefore, it can readily be used as a dopant-free HTM in perovskite solar cells (PSCs) and a conversion efficiency of 10.3% was obtained. The conductivity of the POZ6-2 layer can be markedly enhanced via doping in combination with typical additives, such as 4-tert-butylpyridine (TBP) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). Correspondingly, the efficiency of the PSCs was further improved to 12.3% using doping strategies. Under the same conditions, reference devices based on the well-known HTM Spiro-OMeTAD show an efficiency of 12.8%.
Two novel Acceptor-Donor-Acceptor (A-D-A) structured small molecular (SM-) materials POZ2 and POZ3 using an electron-rich phenoxazine (POZ) unit as a core building block were designed and synthesized. Their unique characteristics, such as suitable energy levels, strong optical absorption in the visible region, high hole mobility, and high conductivity, prompted us to use them both as p-type donor materials (DMs) in SM-bulk heterojunction organic solar cells (BHJ OSCs) and as hole transport materials (HTMs) in CH3NH3PbI3-based perovskite solar cells (PSCs). The POZ(2)-based devices yielded promising power conversion efficiencies (PCEs) of 7.44% and 12.8% in BHJ OSCs and PSCs, respectively, which were higher than the PCEs of 6.73% (BHJ-OSCs) and 11.5% (PSCs) obtained with the POZ3-based devices. Moreover, our results demonstrated that the POZ2 employing the electron-deficient benzothiazole (BTZ) as linker exhibited higher hole mobility and conductivity than that of the POZ3 using thiophene as linker, leading to better device performance both in BHJ-OSCs and PSCs. These results also provide guidance for the molecular design of high charge carrier mobility SM-materials for highly efficient BHJ OSCs and PSCs in the future.
A perylenediimide (PDI) tetramer-based three dimensional (3D) molecular material, termed SFX-PDI4, has been designed, synthesized, and characterized. The low-lying HOMO and LUMO energy levels, high electron mobility and good film-formation property make it a promising electron transport material (ETM) in inverted planar perovskite solar cells (PSCs). The device exhibits a high power conversion efficiency (PCE) of 15.3% with negligible hysteresis, which can rival that of device based on PC61BM. These results demonstrate that three dimensional PDI-based molecular materials could serve as high performance ETMs in PSCs.
An organic-inorganic integrated hole transport layer (HTL) composed of the solution-processable nickel phthalocyanine (NiPc) abbreviated NiPc-(OBu)(8) and vanadium(V) oxide (V2O5) is successfully incorporated into structured mesoporous perovskite solar cells (PSCs). The optimized PSCs show the highest stabilized power conversion efficiency of up to 16.8% and good stability under dark ambient conditions. These results highlight the potential application of organic-inorganic integrated HTLs in PSCs.
The phenoxazine-based acceptor-donor-acceptor structured small-molecule material M1 is used either as a hole-transport material in (CH<inf>3</inf>NH<inf>3</inf>)PbI<inf>3</inf>-perovskite-based solar cells or as photoactive donor material in bulk heterojunction organic solar cells. Excellent power conversion efficiencies of 13.2% and 6.9% are achieved in these two types of photovoltaic devices, respectively.
A D-pi-A type small molecule POZ4 and a A-pi-D-pi-A type small molecule POZ6, in which phenoxazine was used as the central building block and dicyanovinyl was employed as the electron-withdrawing end-group, have been designed and synthesized. Compared with D-pi-A type donor material POZ4, the donor material POZ6 with A-pi-D-pi-A configuration shows much wider response to solar light. An efficiency of 5.60% was obtained for the POZ6: PC71BM based solar cells, and the device fabricated with POZ6:PC71BM (1 : 1) showed a much better balanced hole and electron mobility of 2.24 x 10(-4) cm(2) V-1 s(-1) and 3.17 x 10(-4) cm(2) V-1 s(-1), respectively.
Three new phenothiazine dyes were designed and synthesized, utilizing different acceptor groups. Upon application to TiO2-based solar cells, the effects of different acceptors on the photophysical and electrochemical properties of the dyes and the solar cell performance are detailed. The introduction of a pyridinium unit or 5-carboxy-1-hexyl-2,3,3-trimethyl-indolium unit into the molecular frame as the acceptor instead of cyano acrylic acid can effectively cause a red shift in the absorption spectra. Applied to DSSCs, the devices sensitized by CM502 with the pyridinium unit as the acceptor show the highest efficiency of 7.3%. The devices fabricated with dye CM501 with cyano acrylic acid as the acceptor exhibited the highest V-oc while for the devices sensitized by the dye CM503 with 5-carboxy-1-hexyl2,3,3- trimethyl-3H-indolium unit as the acceptor, the Voc value was the lowest, at 494 mV. The addition of TBP in the electrolyte can improve the performance of DSSCs fabricated using CM501 and CM502, with the Voc value greatly improved but the J(sc) value slightly decreased. However, with the addition of TBP in the electrolyte, the efficiency of the cells sensitized by CM503 dropped significantly (from 4.9% to 1.0% when 0.1 M TBP was added).