Developing renewable energy resources to replace the depleting dodo fuel militias is the biggest challenge for civilisation. Dye-sensitized solar cell [ 1 ] ( DSSC ) has emerged as a cardinal participant amongst the green energy beginnings due to their low cost, easy fiction and high public presentation. [ 2 ] Although a batch of factors determine the efficiency of DSSCs, the behaviour of sensitiser molecules remain extreme of import. A amount of research research labs is devoted to develop new efficient sensitisers. DSSCs sensitized with Ru based dyes have achieved efficiencies around 11 % . [ 3 ] In malice of the high efficiencies, comparatively low extinction coefficients, limited resources and high cost of purification make them less attractive for commercialisation. Recently Gr & A ; auml ; tzel and colleagues reported a Zn ( II ) porphyrin with D-?-A push-pull construction demoing singular power transition efficiency of 12 % when incorporated with Co ( II/III ) tris ( bipyriyl ) -based redox electrolyte under light with standard AM 1.5G simulated sunshine. [ 4 ] Though extension of the porphyrin ?-conjugation by alteration at ?- or meso-positions is an effectual scheme to switch the soaking up into the NIR part, boring synthesis is in general ineluctable. [ 5 ] It is projected that the handiness of high efficiency near-infrared ( NIR ) and panchromatic dyes might farther better the efficiency of DSSCs. Although tremendous literature is available on porphyrin based DSSCs, surprisingly an expanded porphyrin has ne’er been used as the sensitiser for DSSCs boulder clay day of the month.
From the spectroscopic point of position, the expanded porphyrins offer a wide scope of compounds with soaking up energies down to infrared parts. [ 6 ] Expanded porphyrins with more than four pyrrole fractional monetary units in the porphyrinic macrocycle have been widely used in a assortment of applications including anion and metal detectors, [ 7 ] NIR feeling dyes, [ 8 ] two-photon soaking up ( TPA ) stuffs, [ 9 ] and photodynamic therapy [ 10 ] due to their increased pit sizes and alone belongingss in association with drawn-out ?-conjugation. Even though red-shifted soaking up sets of expanded porphyrins match good with the demands for a low energy sensitiser, partially owing to their symmetrical geometries and lacking of proper grounding groups these expanded porphyrins remain unsympathetic for DSSC surveies.
To bring out the potency of using expanded porphyrins to DSSC surveies, herein we report the syntheses, photophysical and photovoltaic belongingss of B chelated oxasmaragdyrins, a category of aromatic core-modified expanded porphyrin with 22 ? negatrons. The oxasmaragdyrin B composites 4a-4e with constructions depicted in Scheme 1, demonstrate panchromatic incident photon-to-current efficiencies ( IPCEs ) , high short-circuit photocurrent densenesss ( Jsc ) , and moderate-to-good overall efficiencies uncovering an chance to develop expanded porphyrin-based high efficiency sensitisers for DSSCs.
[ iˆ? ] Sandeep B. Mane, Dr. Chen-Hsuing Hung
Institute of Chemistry, Academia Sinica, Taipei, 115 Taiwan
Facsimile: ( + ) 886-2-2783-1237
Electronic mail: chhung @ gate.sinica.edu.tw
Home page: hypertext transfer protocol: //www.chem.sinica.edu.tw
Dr. Eric Wei-Guang Diau
Department of Applied Chemistry, National Chiao Tung
University, Hsinchu, 300 ( Taiwan )
Electronic mail: diau @ mail.nctu.edu.tw
Dr. Liyang Luo,
Department of Chemistry,
Chung Yuan Christian University, Chung Li, 32023 ( Taiwan )
Sandeep B. Mane
Department of Chemistry, National Taiwan Normal
University, Taipei, 11677 ( Taiwan )
[ iˆ?iˆ? ] This work has been supported by
Supporting information for this article is available on the WWW under hypertext transfer protocol: //www.angewandte.org or from the writer.
Scheme 1. Synthesis of oxamaragdyrins 4a4e. Reagents and conditions: a ) BF3-OEt2, NEt3, CH2Cl2, RT ; B ) AlCl3, intoxicant, dry CH2Cl2, reflux ; degree Celsius ) KOH ( aq ) , THF, reflux.
The coveted oxasmaragdyrin composites 4a-4e, were prepared in four stairss in nice outputs by mild reaction conditions. The oxasmaragdyrin 1 was prepared from a 3+2 condensation of meso- ( 4-methoxyphenyl ) -dipyrromethane and 16-oxatripyrrane in the presence of TFA as the acid accelerator ( Scheme 1 ) . [ 11 ] The BF2 chelated complex 2 was prepared by handling 1 with triethylamine and BF3-OEt2 in CH2Cl2 at room temperature. The intervention of oxasmaragdyrin-BF2 complex 2 with extra sum of matching intoxicant in presence of AlCl3 at refluxing temperature for 10 min yielded B ( OR ) 2 complexes 3b-3e. [ 12 ] The concluding oxasmaragdyrins 4a-4e were isolated in moderate outputs by hydrolysis of the precursors 2 and 3b-3e with aqueous KOH in THF at reflux conditions. All the concluding compounds and their corresponding precursors were to the full characterized by spectroscopic techniques. In our design, alkoxide with long ironss from C2 to C10 are introduced to screen oxasmaragdyrins from collection and to increase their solubility.
The soaking up spectra of oxasmaragdyrins 4a-4e show split Soret set in 400-500 nanometer and Q-bands in 550-750 nm part as shown in Figure 1a. Markedly, the split Soret set covers a broader scope of soaking up wavelengths than regular porphyrins. Additionally, the Q-bands, which are more intense than typical Zn or free base porphyrins, have a rearward ethio-type form to give the highest ? value at lowest energy band-I at 710 nanometers, switching about 100 nanometers more into the NIR part than Zn ( TPP ) . The broadened Soret sets and high extinction coefficient Q-bands consequence in panchromatic soaking up after adsorbed on TiO2 ( Figure 1b ) to increase the light reaping efficiency and photocurrent denseness in the NIR photo-excitation. Perceptibly, little bathochromic displacement in the soaking up of composites 4b-4e compared to complex 4a indicates the negligible influence of the negatron donating alkoxide ironss to the electronic construction of macrocycle.
Figure 1. Absorption spectra of oxasmaragdyrins 4a-4e a ) in THF, ( in inset: enlargement of Q-bands ) and B ) adsorbed on TiO2.
The structural optimisation on the compounds 4a-4e utilizing the denseness functional theory ( DFT ) under B3LYP functional and the 6-31G footing set gave two-dimensional macrocycles for all oxasmaragdyrins ( see back uping information for more inside informations ) . Two alkoxide long ironss lay on opposite sides of the oxasmaragdyrin plane and extended over the furan ring. Importantly, for all of the molecules, the deliberate molecular orbitals ( MO ) confirm that in the HOMO ( highest occupied molecular orbital ) and HOMO-1 orbitals, bulk of the negatron denseness localizes on the macrocyclic ?-system of oxasmaragdyrin pealing whereas in the lowest unoccupied molecular orbital ( LUMO ) and LUMO+2 orbitals, in add-on to the oxasmaragdyrin ?-system, important sum of negatron denseness populates on the meso-carboxyphenyl anchoring group. The effectual negatron denseness redistribution from oxasmaragdyrin nucleus traveling toward grounding carboxyphenyl pealing upon the photo-excitation from land province to aroused province should ease effectual negatron injection from the aroused province of oxasmaragdyrin to conductivity set of TiO2.
Table 1. Photophysical and Electrochemical informations for oxasmaragdy- rin sensitisers.
?abs [ nm ] ( ? [ 103M?1cm?1 ] ) [ a ]
Eox [ B ]
[ V ]
E ( 0,0 ) [ degree Celsius ]
[ electron volt ]
Eox* [ vitamin D ]
[ V ]
446 ( 278 ) , 474 ( 113 ) ,
706 ( 36 )
450 ( 303 ) , 479 ( 121 ) ,
711 ( 41 )
450 ( 291 ) , 479 ( 117 ) ,
711 ( 38 )
450 ( 242 ) , 480 ( 98 ) ,
710 ( 32 )
450 ( 188 ) , 480 ( 79 ) ,
710 ( 29 )
[ a ] Absorption upper limit of oxasmaragdyrins in THF [ B ] First oxidization potencies vs. NHE determined by CV in THF calibrated by Fc/Fc+ redox twosome. [ 13 ] [ degree Celsius ] E ( 0,0 ) values were estimated from the intersection of the soaking up and emanation spectra. [ 500 ] Excited province oxidization potencies approximated from Eox and E ( 0,0 ) .
Another standard for an effectual negatron injection into TiO2 and fast regeneration of oxidised dye is proper matching of LUMO and HOMO energy degrees with TiO2 carry oning set and energy degree of I?/I3? twosome, severally. The cyclic voltammetry ( CV ) measurings of all oxasmaragdyrins 4a-4e were performed to obtain the oxidation-reduction potencies of the sensitisers and found that all voltammograms observed two reversible oxidizations and one reversible decrease twosomes ( Figure S-15, back uping information ) . The steady potencies and currents under multiple scans during the CV measurings for oxasmaragdyrins suggest high stableness and reversibility of these expanded porphyrins toward oxidation-reduction processes suited for application as sensitiser in DSSCs. The information in Table 1 shows that the oxidization potencies of oxasmaragdyrins 4b-4e, shifted towards less positive by 140 to 170 millivolts ensuing in elevated HOMO degrees compared to oxasmaragdyrin-BF2 4a. However, the decrease potencies of 4b-4e shifted toward more negative by about 120 millivolts than oxasmaragdyrin-BF2 composite. Based on E ( 0,0 ) obtained from soaking up and emanation spectra and the first oxidization potency from CV, the land province oxidization potencies ( Eox ) and aroused province oxidization potencies ( Eox* ) were calculated as listed in Table 1. For all of the oxasmaragdyrin B composites, Eox* are more negative than the conductivity set border of the TiO2 electrode ( -0.5 V vs. normal H electrode ( NHE ) ) while the Eox are more positive than the 0.4 V vs. NHE for the redox potency of I?/I3? . Although the red-shifting in soaking up set of oxasmaragdyrins bases for smaller set spread between HOMO and LUMO orbitals, the electrochemical information confirms the high drive force for both electron injection and dye regeneration.
The BF2 and B ( OR ) 2 chelated oxasmaragdyrins 4a-4e were fabricated into the solar cell devices harmonizing to the processs illustrated in the experimental subdivision. The photovoltaic public presentation of the devices were measured under standard AM 1.5 G simulated solar conditions utilizing THF as the submergence dissolver and are summarized in Table 2. The DSSCs sensitized with oxasmaragdyrin BF2 complex 4a obtained a short circuit photocurrent ( Jsc ) of 12.19 mA cm-2, an unfastened circuit electromotive force ( Voc ) of 0.51 V, and a fill factor ( FF ) of 0.68, which corresponds to overall photon to current transition efficiency of 4.26 % . It is obvious from the informations in Table 2 that the efficiencies of the oxasmaragdyrins 4b-4e lessening as the alkoxy concatenation length addition. Our current information suggest that the lower public presentation of B ( OR ) 2 composites can be attributed to lower dye burdens. The dye lading experiments delivered highest burden of 2.39 – 10?5 mol?1 cm?2 for 4a and 1.54, 1.32, 1.19 and 0.68 – 10?5 mol?1 cm?2 for the B ( OR ) 2 complexes 4b-4e, severally. Apparently, a longer alkyl concatenation will dramatically increase the intermolecular steric repulsive force ensuing in lower dye burden and accordingly diminishing the photocurrent denseness. The presence of chenodeoxycholic acid ( CDCA ) as an additive to the oxasmaragdyrin dyes failed to further better the photon to current transition efficiencies. For all the measurings, tetrahydrofuran was picked as the dissolver for dye surface assimilation to TiO2 for the interest of a higher solubility. Strikingly, utilizing ethyl alcohol as the submergence dissolver for 4a, calculated a maximal efficiency of 4.95 % with a Jsc of 11.19 mA cm-2, a Voc of 0.61 V, and a fill factor of 0.72.
Table 2. Photovoltaic belongingss of devices with 4a-4e as the sensitisers. [ a ]
Jsc [ mA cm-2 ]
Voc [ V ]
FF [ % ]
? [ % ]
4.95 [ B ]
[ a ] Submergence in THF at 25 oC for 24 H ; measured at AM 1.5G one Sun ; [ b ] Immersion in EtOH at room temperature for 6 H.
The current-voltage features and incident-photon-to-electron efficiency ( IPCE ) action spectra of the corresponding devices are given in Figure 2. IPCE spectra of the oxasmaragdyrins were similar with the optical density of the dyes adsorbed on TiO2. Consistent with the efficiency measurings ; the oxasmaragdyrin 4a gave outstanding transition efficiency in the part of Soret set covering soaking up wavelengths from 380 to 520 nanometers with a upper limit of 75 % efficiency at 410 nanometer. The chasing off of the Soret soaking up has overlapped with the increasing IPCE of Q set to cover the full seeable part with a maximal efficiency of 52 % at 702 nanometer. The oncoming of the IPCE spectrum was at 800 nanometer which showed a bathochromic displacement of about 100 nanometers compared with the D-?-A zinc porphyrin dye YD-2 and the IPCE in Q set part was good comparable with phthalocyanines. [ 5d,14 ] Usually the B ( OR ) 2 chelated oxasmaragdyrins give lower IPCEs in both Soret set and Q-band part except that the efficiency reaches near 80 % at 440 nanometer for B ( OEt ) 2 chelated oxasmaragdyrin 4b. The abnormalcy can besides be visualized from the J-V curve with 4b exhibiting the highest Voc among devices prepared utilizing THF as the submergence dissolver.
Figure 2. a ) J-V features and B ) IPCE action spectra of DSSCs fabricated with oxasmaragdyrins 4a-4e measured under 100 % Sun ( AM 1.5 G ) .
From a better matching of the peak forms between soaking up spectra in solution provinces and in solid provinces for oxasmaragdyrins-B ( OR ) 2 ( Figure S-14 ) , it appears that the alkoxy substituents can efficaciously forestall the dye collection. However, the ascertained lower cyberspace potencies for cells with B ( OR ) 2 ( R = C4H9, C7H15 and C10H21 ) chelated oxasmaragdyrins as sensitiser suggested that the reduced dye burdens and hence lower surface coverage will promote the back negatron transportation from TiO2 surface to I3? . The highest Voc for 4b is presumptively due to a delicate balance between the positive consequence of a lesser grade of dye collection and the negative effects of reduced dye lading from steric constrain.
In decision, without extended fictions on the substituents of dye and before dog-tired device optimisations, we were able to show for the first clip that B composites of oxasmaragdyrin, a core-modified expanded porphyrin, can be effectual sensitisers for DSSC. In contrast with the comparatively low efficiencies for the devices utilizing BODIPY as the sensitiser, [ 15 ] B chelated oxasmaragdyrins are aromatic compounds with high extinction coefficients, high stableness, and good power transition efficiency. The photophysical word pictures suggest that the B chelation to oxasmaragdyrins can cut down intermolecular collection and besides these dyes exhibit the coveted redox potency required for an effectual sensitiser in DSSCs. More significantly, wide soaking up distributing the full seeable part and its lower energy Q set covering the NIR part make this category of compounds an optimistic campaigner for being one of the future choices of porphyrin-based sensitising dyes. Given that the expanded porphyrins have already demonstrated alone photophysical belongingss with soaking ups making IR part, more surveies to use the expanded porphyrins as the sensitiser for DSSC are ongoing in our lab.
Photovoltaic word picture: The current-voltage features of the devices were measured with a digital beginning metre ( Keithley 2400 ) under one Sun AM 1.5G irradiation from a solar simulator ( SAN-EI, XES-502S ) calibrated with a silicon-based mention cell ( S1133, Hamamatsu ) . The incident photons to current efficiency ( IPCE ) spectra of the corresponding devices were recorded with a system consisting a Xenon lamp ( PTi A-1010, 150 W ) , a monochromator ( PTi, 1200 g mm-1 blazed at 500 nanometer ) , long passed filter and a beginning metre.
Solar cell fiction: TiO2 nanoparticles were prepared with a sol-gel method as reported. [ 16 ] A paste composed of TiO2 nano atoms ( 20 nanometer ) was coated with screen publishing on a TiCl4-pretreated FTO glass ( TEC7, Hartford, USA ) . A dispersing bed ( 200-600 nanometer ) was screen-printed to boot on the active bed to better the public presentation of the solar cell. The TiO2 movies were annealed harmonizing to a programmed process: warming at 80 oC for 15 min ; heating at 135 oC for 10 min ; heating at 325 oC for 30 min ; heating at 375 oC for 5 min ; heating at 450 oC for 15 min ; and warming at 500 oC for 15 min. The thickness of the transparent active bed was 10 µm and that of the dispersing bed was 4 µm. The TiO2 movies ( active size 0.4-0.4 cm2 ) were sensitized by dunking it in the solution of oxasmaragdyrins ( 0.2 millimeter ) in THF for 24 H at ambient temperature. After being washed with ethyl alcohol, the allergic working electrode was assembled with a Pt counter electrode and sealed with a hotmelt movie. An electrolyte solution ( 0.05 M I2, 0.1 M LiI, 0.6 M 1,2-dimethyl-3-propylimidazolium iodide ( DMPII ) , and 0.6 M tert-butyl pyridine ( t-BP ) in a mixture of acetonitrile and valeronitrile 18/15 ( v/v ) was used in all devices.
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Keywords: dye sensitized solar cells · porphyrinoids · energy transition · smaragdyrins
Entry for the Table of Contentss
Dye Sensitized Solar cell
Expand it Further: Liquid DSSCs incorporating a 22-?-electron expanded core-modified oxasmaragdyrin as the sensitiser with panchromatic soaking up extended to the near-IR part are prepared to accomplish a promising energy transition efficiency up to 4.95 % , with a short-circuit current denseness ( Jsc ) of 11.19 mA cm-2, an open-circuit electromotive force ( Voc ) of 610 millivolts and a fill factor ( FF ) of 0.72.
S. B. Mane, L. Luo, Eric W.-G. Diau, C. H. Hung* __________ Page – Page
Oxasmaragdyrin Boron Complexes: First High-Efficiency Panchromatic Expanded Core-Modified Porphyrin for DSSCs.