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Mohammad Khaja Nazeeruddin - One of the best experts on this subject based on the ideXlab platform.
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thiocyanate free ru ii Sensitizers with a 4 4 dicarboxyvinyl 2 2 bipyridine anchor for dye sensitized solar cells
Advanced Functional Materials, 2013Co-Authors: Pitai Chou, Kuanlin Wu, Wanping Ku, Shengwei Wang, Aswani Yella, Mohammad Khaja NazeeruddinAbstract:A new class of thiocyanate-free Ru(II) Sensitizers with 4,4-dicarboxyvinyl-2,2-bipyridine anchor and two trans-oriented pyrid-2-yl pyrazolate (or triazolate) functional chromophores is synthesized, characterized, and evaluated in dye-sensitized solar cells (DSCs). Despite their enhanced red response and absorptivity when compared to the parent Sensitizer TFRS-2 that possesses standard 4,4-dicarboxyl-2,2-bipyridine anchor and shows the best conversion efficiency of = 9.82%, the newly synthesized carboxyvinyl-pyrazolate Sensitizers, TFRS-11TFRS-13, exhibit inferior performance characteristics in terms of short-circuit current density (JSC), open-circuit voltage (VOC), and power conversion efficiency (), the latter being recorded to be in the range 5.607.62%. The reduction in device efficiencies is attributed to a combination of poor packing of these Sensitizers on the TiO2 surface and less positive ground-state oxidation potentials, which, respectively, increase charge recombination with I3 in electrolytes and impede the regeneration of Sensitizers by I anions. The latter obstacle can be circumvented in part by the replacement of the pyrazolates with triazolates, forming the TFRS-14 Sensitizer, which exhibits an improved JSC, VOC, and of 16.4 mAcm2, 0.77 V, and 9.02%, respectively.
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harnessing the open circuit voltage via a new series of ru ii Sensitizers bearing iso quinolinyl pyrazolate ancillaries
Energy and Environmental Science, 2013Co-Authors: John N Clifford, Emilio Palomares, Pitai Chou, Yun Chi, Shihhung Liu, Mohammad Khaja NazeeruddinAbstract:A novel class of Ru(II) Sensitizers (TFRS-51–TFRS-54) with a 4,4′-dicarboxy-2,2′-bipyridine anchoring ligand and two trans-oriented isoquinolinyl (or quinolinyl) pyrazolate ancillaries were designed, characterized and used to fabricate dye sensitized solar cell (DSC) devices. In sharp contrast to Ru(II) Sensitizers that employ functionalized thiophene appendages in their ancillary bipyridal ligands, the extended π-conjugation introduced by the isoquinolinyl or quinolinyl groups improves the optical absorptivity, particularly for the absorption located at ∼500 nm when compared with the parent Sensitizer TFRS-1 possessing less conjugated 5-pyrid-2-yl pyrazolate ancillaries. As a result, DSCs incorporated with these dyes show much improved JSC compared with the reference device. Moreover, the use of bulky t-butyl substituents on the ancillary ligands improves the cell performance with excellent VOC of up to 830 mV recorded. Also, the addition of tetra-n-butyl ammonium deoxycholate [TBA][DOC] as co-adsorbent to the dye solution further improves the power conversion efficiency (η). The best solar cell parameters recorded were JSC = 16.3 mA cm−2, VOC = 860 mV, FF = 0.72, and η = 10.1% for a device sensitized with TFRS-52. The markedly high open-circuit voltage is confirmed by the longer electron lifetime revealed in transient photovoltage (TPV) measurement versus the TFRS-1 Sensitizer, and is probably derived from a combination of the higher conduction band edge of TiO2 induced by the in situ metathesis of carboxylate anchors and the reduced recombination contributed by the bulky Sensitizer.
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Effect of anchoring groups in zinc phthalocyanine on the dye-sensitized solar cell performance and stability
Chemical Science, 2011Co-Authors: Miguel García-iglesias, Jun-ho Yum, Robin Humphry-baker, M. Zakeeruddin, Peter Pechy, Purificación Vázquez, Emilio Palomares, Mohammad Khaja Nazeeruddin, Tomás TorresAbstract:We have designed and developed an unsymmetrical zinc phthalocyanine (TT9) Sensitizer that consists of three tert-butyl and two carboxylic acid groups that act as “push” and “pull”, respectively. The two carboxylic acid groups graft the Sensitizer onto the semiconductor surface resulting in enhanced stability under heat and light compared to the similar unsymmetrical zinc phthalocyanine (TT1) Sensitizer that consists of three tert-butyl and only one carboxylic acid groups. The solar cells containing the TT9 and TT1 Sensitizers with non-volatile electrolyte were subjected to light soaking conditions at 60 °C. Under these conditions, the short circuit current of the TT1 sensitized solar cell after 1000 h decreases to half of its initial value where as the TT9 sensitized solar cell remained the same demonstrating the influence of number of anchoring groups on the stability of zinc phthalocyanine sensitized solar cells.
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first principles modeling of the adsorption geometry and electronic structure of ru ii dyes on extended tio2 substrates for dye sensitized solar cell applications
Journal of Physical Chemistry C, 2010Co-Authors: Filippo De Angelis, Mohammad Khaja Nazeeruddin, Simona Fantacci, Annabella Selloni, Michael GrätzelAbstract:We report a systematic density functional theory (DFT) computational investigation of Ru(II) Sensitizer/TiO2 systems relevant to dye-sensitized solar cells (DSSCs). Focusing on the prototypical N719 and the recently introduced YE05 Sensitizers, and considering large slab and cluster models for TiO2, we have systematically studied the influence of the molecular adsorption geometry, counterions, and surface protonation on the electronic structure of the dye/semiconductor systems by means of Car−Parrinello molecular dynamics combined with single-point hybrid functional calculations of the electronic properties. Our results show that the homoleptic N719 and YE05 dyes, both bearing two bipyridine ligands functionalized with four carboxylic groups, adsorb onto the TiO2 surface by exploiting three carboxylic groups. The bulky TBA counterions employed in N719 cause a modest energy down-shift of the TiO2 conduction band, whereas the smaller Na+ counterions, which can access the surface more closely, lead to a larg...
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high extinction coefficient antenna dye in solid state dye sensitized solar cells a photophysical and electronic study
Journal of Physical Chemistry C, 2008Co-Authors: Henry J Snaith, Mohammad Khaja Nazeeruddin, Chedarampet S Karthikeyan, Annamaria Petrozza, Joel Teuscher, Jacquese Moser, Mukundan ThelakkatAbstract:We present a photophysical and device-based investigation of a new bipyridyl−NCS ruthenium complex Sensitizer with an extended π system, in both sensitized TiO2 and incorporated into solid-state dye-sensitized solar cells. We compare this new Sensitizer to an analog dye without the extended π system. We observe very similar excited-state absorption spectra and charge recombination kinetics for the two systems. However, the π-extended senstizer has a phenomenally enhanced molar extinction coefficient which translates into far greater light harvesting and current collection in solid-state dye-sensitized solar cells. We also infer from transient photovoltage measurements that positioning the pendent extended π system away from the TiO2 surface has induced a favorable dipole shift, generating enhanced open-circuit voltage. The resulting power conversion efficiency for the solar cell has been increased from 2.4% to 3.2% when comparing the new Sensitizer to an analogy with no pendent group.
Shaik M Zakeeruddin - One of the best experts on this subject based on the ideXlab platform.
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donor π acceptors containing the 10 1 3 dithiol 2 ylidene anthracene unit for dye sensitized solar cells
Chemistry: A European Journal, 2012Co-Authors: Pierreantoine Bouit, Robin Humphrybaker, Juan Luis Delgado, Shaik M Zakeeruddin, Magdalena Marszalek, Rafael Viruela, Enrique Orti, Nazario MartinAbstract:Two donoracceptor molecular tweezers incorporating the 10-(1,3-dithiol-2-ylidene)anthracene unit as donor group and two cyanoacrylic units as accepting/anchoring groups are reported as metal-free Sensitizers for dye-sensitized solar cells. By changing the phenyl spacer with 3,4-ethylenedioxythiophene (EDOT) units, the absorption spectrum of the Sensitizer is red-shifted with a corresponding increase in the molar absorptivity. Density functional calculations confirmed the intramolecular charge-transfer nature of the lowest-energy absorption bands. The new dyes are highly distorted from planarity and are bound to the TiO2 surface through the two anchoring groups in a unidentate binding form. A power-conversion efficiency of 3.7?% was obtained with a volatile CH3CN-based electrolyte, under air mass 1.5 global sunlight. Photovoltage decay transients and ATR-FTIR measurements allowed us to understand the photovoltaic performance, as well as the surface binding, of these new Sensitizers.
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significant improvement of dye sensitized solar cell performance by small structural modification in π conjugated donor acceptor dyes
Advanced Functional Materials, 2012Co-Authors: Stefan Haid, Joel Teuscher, Jacquese Moser, Robin Humphrybaker, Shaik M Zakeeruddin, Magdalena Marszalek, Amaresh Mishra, Mateusz Wielopolski, Peter BauerleAbstract:Two donor-π-acceptor (D-π-A) dyes are synthesized for application in dye- sensitized solar cells (DSSC). These D-π-A Sensitizers use triphenylamine as donor, oligothiophene as both donor and π-bridge, and benzothiadiazole (BTDA)/cyanoacrylic acid as acceptor that can be anchored to the TiO2 sur- face. Tuning of the optical and electrochemical properties is observed by the insertion of a phenyl ring between the BTDA and cyanoacrylic acid acceptor units. Density functional theory (DFT) calculations of these Sensitizers provide further insight into the molecular geometry and the impact of the additional phenyl group on the photophysical and photovoltaic performance. These dyes are investigated as Sensitizers in liquid-electrolyte-based dye-sensitized solar cells. The insertion of an additional phenyl ring shows significant influence on the solar cells’ performance leading to an over 6.5 times higher efficiency (η = 8.21%) in DSSCs compared to the Sensitizer without phenyl unit (η = 1.24%). Photophysical investigations reveal that the insertion of the phenyl ring blocks the back electron transfer of the charge separated state, thus slowing down recombination processes by over 5 times, while maintaining efficient electron injection from the excited dye into the TiO2-photoanode.
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cobalt redox mediators for ruthenium based dye sensitized solar cells a combined impedance spectroscopy and near ir transmittance study
Journal of Physical Chemistry C, 2011Co-Authors: Yeru Liu, James R Jennings, Yao Huang, Qing Wang, Shaik M ZakeeruddinAbstract:Dye-sensitized solar cells with power conversion efficiencies of up to 6.5% have been fabricated using a cobalt tris-bipyridyl redox mediator with the cis-diisothiocyanato-(2,2′-bipyridyl-4,4′-dicarboxylic acid)-(2,2′-bipyridyl-4,4′-dinonyl) ruthenium(II) (Z907) Sensitizer. This represents a significant improvement in efficiency compared with previous reports using ruthenium Sensitizers. In situ near-IR transmittance measurements in conjunction with electrochemical impedance spectroscopy have been used to explain the difference in performance between DSCs using Z907 and another benchmark Sensitizer cis-diisothiocyanato-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium(II) bis(tetrabutylammonium) (N719). It is found that the small-perturbation electron diffusion length (Ln) is significantly longer in Z907 cells compared with that in N719 cells, which can explain most of the difference in performance. It is also shown that the longer Ln in Z907 cells is caused by inhibited recombination, as opposed to fa...
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efficient electron transfer and Sensitizer regeneration in stable π extended tetrathiafulvalene sensitized solar cells
Journal of the American Chemical Society, 2010Co-Authors: Sophie Wenger, Joel Teuscher, Pierreantoine Bouit, Qianli Chen, Davide Di Censo, Robin Humphrybaker, Jacquesedouard Moser, Juan Luis Delgado, Nazario Martin, Shaik M ZakeeruddinAbstract:The development of metal-free organic Sensitizers is a key issue in dye-sensitized solar cell research. We report successful photovoltaic conversion with a new class of stable tetrathiafulvalene derivatives, showing surprising electrochemical and kinetic properties. With time-resolved spectroscopy we could observe highly efficient regeneration of the photo-oxidized tetrathiafulvalene Sensitizers, which were attached to a mesoporous TiO2 film, by a redox mediator in the pores (iodide/tri-iodide), even though the measured driving force for regeneration was only ∼150 mV. This important proof-of-concept shows that Sensitizers with a small driving force, i.e. the oxidation potential of the Sensitizer is separated from the redox potenial of the mediator by as little as 150 mV, can operate functionally in dye-sensitized solar cells and eventually aid to reduce photovoltage losses due to poor energetic alignment of the materials.
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passivation of nanocrystalline tio2 junctions by surface adsorbed phosphinate amphiphiles enhances the photovoltaic performance of dye sensitized solar cells
Dalton Transactions, 2009Co-Authors: Mingkui Wang, Peter Pechy, Hong Lin, Shaik M ZakeeruddinAbstract:We report a new class of molecular insulators that electronically passivate the surface of nanocrystalline titania films for high performance dye sensitized solar cells (DSC). Using electrical impedance measurements we demonstrate that co-adsorption of dineohexyl bis-(3,3-dimethyl-butyl)-phosphinic acid (DINHOP), along with the amphiphilic ruthenium Sensitizer Z907Na increased substantially the power output of the cells mainly due to a retardation of interfacial recombination of photo-generated charge carriers. The use of phosphinates as anchoring groups opens up new avenues for modification of the surface by molecular insulators, Sensitizers and other electro-active molecules to realize the desired optoelectronic performance of devices based on oxide junctions.
Michael Grätzel - One of the best experts on this subject based on the ideXlab platform.
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first principles modeling of the adsorption geometry and electronic structure of ru ii dyes on extended tio2 substrates for dye sensitized solar cell applications
Journal of Physical Chemistry C, 2010Co-Authors: Filippo De Angelis, Mohammad Khaja Nazeeruddin, Simona Fantacci, Annabella Selloni, Michael GrätzelAbstract:We report a systematic density functional theory (DFT) computational investigation of Ru(II) Sensitizer/TiO2 systems relevant to dye-sensitized solar cells (DSSCs). Focusing on the prototypical N719 and the recently introduced YE05 Sensitizers, and considering large slab and cluster models for TiO2, we have systematically studied the influence of the molecular adsorption geometry, counterions, and surface protonation on the electronic structure of the dye/semiconductor systems by means of Car−Parrinello molecular dynamics combined with single-point hybrid functional calculations of the electronic properties. Our results show that the homoleptic N719 and YE05 dyes, both bearing two bipyridine ligands functionalized with four carboxylic groups, adsorb onto the TiO2 surface by exploiting three carboxylic groups. The bulky TBA counterions employed in N719 cause a modest energy down-shift of the TiO2 conduction band, whereas the smaller Na+ counterions, which can access the surface more closely, lead to a larg...
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high performance liquid and solid dye sensitized solar cells based on a novel metal free organic Sensitizer
Advanced Materials, 2008Co-Authors: Mingkui Wang, Robin Humphrybaker, Shaik M Zakeeruddin, Feifei Gao, Dong Shi, Peng Wang, Guangliang Zhang, Michael GrätzelAbstract:A new metal-free organic Sensitizer (see figure) for high-performance and applicable dye-sensitized solar cells is presented. In combination with a solvent-free ionic liquid electrolyte, a similar to 7% cell made with this Sensitizer shows all excellent stability measured under thermal and light-soaking dual stress. For the first time a 4.8% efficiency is reached for all-solid-state dye-sensitized solar cells based oil all organic dye.
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Influence of the Sensitizer Adsorption Mode on the Open-Circuit Potential of Dye-Sensitized Solar Cells
Nano letters, 2007Co-Authors: Filippo De Angelis, Simona Fantacci, Annabella Selloni, Michael Grätzel, Mohammad Khaja NazeeruddinAbstract:We report a combined experimental and theoretical study on the origin of the different open circuit potentials observed in dye-sensitized solar cells using Ru(II)-polypyridyl homoleptic and heteroleptic Sensitizers. We have measured the photovoltaic data of different Sensitizers and used DFT calculations to analyze the electronic structure of dye-sensitized TiO2 nanoparticles. Heteroleptic Sensitizers adsorb onto TiO2 via a single bipyridine, leading to a TiO2 conduction band downshift and overall reduction of the cell open circuit potential.
Kuanlin Wu - One of the best experts on this subject based on the ideXlab platform.
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thiocyanate free ruthenium ii Sensitizers for dye sensitized solar cells based on the cobalt redox couple
Chemsuschem, 2014Co-Authors: Emilio Palomares, John N Clifford, Filippo De Angelis, Kuanlin Wu, Shengwei Wang, Yella Aswani, Maria Grazia Lobello, Edoardo Mosconi, Wanping KuAbstract:Two thiocyanate-free ruthenium(II) Sensitizers, TFRS-41 and TFRS-42, with distinctive dialkoxyphenyl thienyl substituents were successfully prepared and tested for potential applications in making dye-sensitized solar cells (DSCs). Subsequent device fabrication was conducted by using a [Co(bpy)(3)](2+/3+)-based (bpy=2,2-bipyridine) electrolyte, for which the best performance data, namely, J(SC)=13.11mAcm(-2), V-OC=862mV, fill factor=0.771, and =8.71%, were recorded for the Sensitizer TFRS-42 with a 2,6-dialkoxyphenyl substituent under AM1.5G irradiation. The markedly higher V-oc value was confirmed by the longer electron lifetime revealed in transient photovoltage (TPV) measurements versus the TFRS-1 Sensitizer. In addition, DFT calculation and detailed first-principles computational analysis were conducted to provide a rationale for the observed trends in their photovoltaic performances and electron lifetimes, with reference to different performances exhibited by three thiocyanate-free Sensitizers, TFRS-1, TFRS-41 and TFRS-42, versus Z907 reference. Through the proper control of peripheral substituents, the thiocyanate-free ruthenium(II)-based DSC Sensitizers can positively influence the performances of DSCs, with better light-harvesting capability and suppressed charge recombination, for DSC cells fabricated by using a [Co(bpy)(3)](2+/3+)-based electrolyte.
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thiocyanate free ru ii Sensitizers with a 4 4 dicarboxyvinyl 2 2 bipyridine anchor for dye sensitized solar cells
Advanced Functional Materials, 2013Co-Authors: Pitai Chou, Kuanlin Wu, Wanping Ku, Shengwei Wang, Aswani Yella, Mohammad Khaja NazeeruddinAbstract:A new class of thiocyanate-free Ru(II) Sensitizers with 4,4-dicarboxyvinyl-2,2-bipyridine anchor and two trans-oriented pyrid-2-yl pyrazolate (or triazolate) functional chromophores is synthesized, characterized, and evaluated in dye-sensitized solar cells (DSCs). Despite their enhanced red response and absorptivity when compared to the parent Sensitizer TFRS-2 that possesses standard 4,4-dicarboxyl-2,2-bipyridine anchor and shows the best conversion efficiency of = 9.82%, the newly synthesized carboxyvinyl-pyrazolate Sensitizers, TFRS-11TFRS-13, exhibit inferior performance characteristics in terms of short-circuit current density (JSC), open-circuit voltage (VOC), and power conversion efficiency (), the latter being recorded to be in the range 5.607.62%. The reduction in device efficiencies is attributed to a combination of poor packing of these Sensitizers on the TiO2 surface and less positive ground-state oxidation potentials, which, respectively, increase charge recombination with I3 in electrolytes and impede the regeneration of Sensitizers by I anions. The latter obstacle can be circumvented in part by the replacement of the pyrazolates with triazolates, forming the TFRS-14 Sensitizer, which exhibits an improved JSC, VOC, and of 16.4 mAcm2, 0.77 V, and 9.02%, respectively.
Peng Wang - One of the best experts on this subject based on the ideXlab platform.
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conjugation of selenophene with bipyridine for a high molar extinction coefficient Sensitizer in dye sensitized solar cells
Inorganic Chemistry, 2009Co-Authors: Feifei Gao, Yueming Cheng, Shi Liu, Dong Shi, Peng WangAbstract:A high molar extinction coefficient heteroleptic polypyridyl ruthenium Sensitizer, featuring a conjugated electron-rich selenophene unit in its ancillary ligand, has been synthesized and demonstrated as an efficient Sensitizer in dye-sensitized solar cells. A nanocrystalline titania film stained with this Sensitizer shows improved optical absorptivity, which is highly desirable for dye-sensitized solar cells with a thin photoactive layer. With preliminary testing, this Sensitizer has already achieved a high efficiency of 10.6% measured under the air mass 1.5 global conditions.
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high performance liquid and solid dye sensitized solar cells based on a novel metal free organic Sensitizer
Advanced Materials, 2008Co-Authors: Mingkui Wang, Robin Humphrybaker, Shaik M Zakeeruddin, Feifei Gao, Dong Shi, Peng Wang, Guangliang Zhang, Michael GrätzelAbstract:A new metal-free organic Sensitizer (see figure) for high-performance and applicable dye-sensitized solar cells is presented. In combination with a solvent-free ionic liquid electrolyte, a similar to 7% cell made with this Sensitizer shows all excellent stability measured under thermal and light-soaking dual stress. For the first time a 4.8% efficiency is reached for all-solid-state dye-sensitized solar cells based oil all organic dye.