Ashraful Islam

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Organization: National Institute for Materials Science , Japan
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Co-reporter:Narra Vamsi Krishna, Jonnadula Venkata Suman Krishna, Surya Prakash Singh, Lingamallu Giribabu, Ashraful Islam, and Idriss Bedja
The Journal of Physical Chemistry C November 22, 2017 Volume 121(Issue 46) pp:25691-25691
Publication Date(Web):October 26, 2017
DOI:10.1021/acs.jpcc.7b07692
Porphyrin-based sensitizers have attracted significant attention due to their excellent performance in dye-sensitized solar cells (DSSCs). Herein, a novel electron donor−π-bridge–electron acceptor (D−π–A) based porphyrin sensitizer having strong electron donating methyl phenanthroimidazole ring and ethynylcarboxyphenyl group at meso- position of porphyrin framework (LG11) was designed and applied as sensitizer in DSSC. To reduce the undesirable loss of open-circuit voltage (VOC) caused by dye aggregation and charge recombination effect, phenyl (LG12) or hexyl phenyl chains (LG13 and LG14) were attached to the phenanthroimidazole moiety. The introduction of a simple thiophene unit between the porphyrin and carboxylic acid anchoring group (LG14) has enabled further extension of the absorption to a longer wavelength. Compared to LG11 and LG12, hexyl phenyl-substituted LG13 and LG14 effectively reduced the dye aggregation and allowed enhancement of VOC to 460 and 650 mV. Both LG13 and LG14 sensitizers exhibit broader and redshift incident photon conversion efficiency spectra and resulted in highest JSC of 14.2 and 15.5 mA cm–2, respectively. Because of all aforesaid properties, LG13 and LG14 dyes show photovoltaic conversion efficiencies of 6.25% and 7.45%, respectively. Further, a cosensitization of LG14 with an organic molecule (HC5) to increase the absorption valley in the visible region has seen efficiency enhanced to 8.27%. This work provides a potential approach to molecular design of porphyrin sensitizers and selection of cosensitizers to build better efficient and stable DSSC system. We have adopted intensity-modulated photo voltage spectroscopy and nanosecond laser flash photolysis spectroscopy to explain the efficiency and structure relationship of these LG11-LG14 sensitizers.
Co-reporter:Lingamallu Giribabu;Naresh Duvva;Surya Prakash Singh;Liyuan Han;Idriss M. Bedja;Ravindra Kumar Gupta
Materials Chemistry Frontiers 2017 vol. 1(Issue 3) pp:460-467
Publication Date(Web):2017/03/09
DOI:10.1039/C6QM00070C
Two new metal-free organic sensitizers have been designed based on tetrathiafulvalene scaffolds by implementing a donor–π–acceptor (D–π–A) approach in which thioalkyl substituted tetrathiafulvalene acts as a donor, substituted anthracene as a π-spacer and cyanoacrylic acid acts as an acceptor as well as an anchoring group. Spectroscopic, electrochemical and DFT studies confirmed the molecular integrity of both sensitizers. The onset of absorption of both sensitizers extends up to 600 nm in solution and up to 700 nm on nanocrystalline TiO2. DFT studies specified that the HOMO is delocalized over the anthracene as well as the dithiole units, and the LUMO is delocalized over the anchoring group in both sensitizers. The new sensitizers have shown an improved efficiency of 7.15% in dye-sensitized solar cells using an I−/I3− redox couple. The enhanced efficiency might be due to the thioalkyl group wrapping over the anthracene π-spacer to prevent the recombination of electrons in the TiO2 conduction band. Recombination studies indicate the regeneration of the oxidized dye due to the redox couple.
Co-reporter:Lingamallu Giribabu;Naresh Duvva;Seelam Prasanthkumar;Surya Prakash Singh;Liyuan Han;Idriss Bedja;Ravindra Kumar Gupta
Sustainable Energy & Fuels (2017-Present) 2017 vol. 1(Issue 2) pp:345-353
Publication Date(Web):2017/03/29
DOI:10.1039/C6SE00014B
Four new extended π-conjugated tetrathiafulvalene (ex-TTF) based dyes featuring a donor–π–acceptor (D–π–A) configuration with varying π-spacers and anchoring groups were synthesized and characterized. The sensitizer having the 4-ethynyl phenyl π-spacer (G4) shows red shifted absorption maxima in comparison with the sensitizer having only the phenyl π-spacer (G2). All four sensitizers undergo reversible oxidations to form stable radical cations. TDDFT calculations highlighted that the LUMO of the G4 sensitizer is more stabilized by the incorporation of the ethynyl group between the π-spacer and the cyanoacrylic acid anchoring group that aid to inject electrons efficiently into TiO2 thereby resulting in an enhanced power conversion efficiency of 6.36% when compared to the other derivatives, which is also confirmed by the intensity-modulated photovoltage spectroscopy (IMVS) method. Kinetic studies demonstrated that fast regeneration of the oxidized dye by the redox couple is an important factor behind enhanced efficiencies in solar cells. Finally, the performance of the present sensitizers is compared to that of previously reported sensitizers.
Co-reporter:Guohua Wu, Ryuji Kaneko, Kosuke Sugawa, Ashraful Islam, Idriss Bedja, Ravindra Kumar Gupta, Liyuan Han, Joe Otsuki
Dyes and Pigments 2017 Volume 140(Volume 140) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.dyepig.2017.01.061
•Novel Ru dyes with NˆNˆN or C−ˆNˆN pattern as an auxiliary ligand were designed.•Introduction of 2-hexylthiophene unit lowers the molar extinction coefficients.•The dyes with C−ˆNˆN pattern exhibited the IPCE up to a near-IR region (∼950 nm).•The efficiency of DSSC is higher with NˆNˆN complex than with C−ˆNˆN complex.Four new bistridentate Ru(II) complexes having a combination of ligands, 4,4′-dicarboxy-2,2′:6,2″-terpyridine or its 2-hexylthiophene-substituted derivative as the anchoring ligand on one hand and one of tetrazolylpyridine-based ligands having a NˆNˆN coordination pattern or C−ˆNˆN coordination pattern as the auxiliary ligand on the other are reported as sensitizers for dye-sensitized solar cells (DSSCs), along with their spectroscopic, electrochemical, and theoretical characterizations. For the anchoring ligand, the introduction of 2-hexylthiophene unit leads to narrower spectral response and lower molar extinction coefficients and a smaller driving force for dye regeneration. For the ancillary ligand, the cyclometalating RuC bond induces a red shift in absorption compared with a RuN bond and thus affords a photocurrent generation at wavelengths of up to 950 nm. Further, the overall efficiencies of DSSCs are higher with the NˆNˆN complexes than with the C−ˆNˆN complexes, mainly due to higher open-circuit voltages (Voc). Overall, the DSSC based on the bistetrazolate dye without the hexylthiophene unit for the anchoring ligand and having the NˆNˆN coordination pattern for the auxiliary ligand exhibited the highest efficiency of 5.9% when employing 0.5 M t-butylpyridine in the electrolyte.Download high-res image (159KB)Download full-size image
Co-reporter:Ashraful Islam, Md. Akhtaruzzaman, Towhid H. Chowdhury, Chuanjiang Qin, Liyuan Han, Idriss M. Bedja, Romain Stalder, Kirk S. Schanze, and John R. Reynolds
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 7) pp:4616
Publication Date(Web):January 26, 2016
DOI:10.1021/acsami.5b11134
Dye-sensitized solar cells (DSSCs) based on a donor–acceptor–donor oligothienylene dye containing benzothiadiazole (T4BTD-A) were cosensitized with dyes containing cis-configured squaraine rings (HSQ3 and HSQ4). The cosensitized dyes showed incident monochromatic photon-to-current conversion efficiency (IPCE) greater than 70% in the 300–850 nm wavelength region. The individual overall conversion efficiencies of the sensitizers T4BTD-A, HSQ3, and HSQ4 were 6.4%, 4.8%, and 5.8%, respectively. Improved power conversion efficiencies of 7.0% and 7.7% were observed when T4BTD-A was cosensitized with HSQ3 and HSQ4, respectively, thanks to a significant increase in current density (JSC) for the cosensitized DSSCs. Intensity-modulated photovoltage spectroscopy results showed a longer lifetime for cosensitized T4BTD-A+HSQ3 and T4BTD-A+HSQ4 compared to that of HSQ3 and HSQ4, respectively.Keywords: benzothiadiazole dye; co-sensitization; dye-sensitized solar cell; incident photon to current conversion efficiency; squaraine dye
Co-reporter:G. Hanumantha Rao, A. Venkateswararao, L. Giribabu, Liyuan Han, Idriss Bedja, Ravindra Kumar Gupta, Ashraful Islam and Surya Prakash Singh  
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 21) pp:14279-14285
Publication Date(Web):19 Apr 2016
DOI:10.1039/C6CP01669C
A combination of squaraine-based dyes (SPSQ1 and SPSQ2) and a ruthenium-based dye (N3) were chosen as co-sensitizers to construct efficient dye-sensitized solar cells. The co-sensitization of squaraine dyes with N3 enhanced their light-harvesting properties as a result of the broad spectral coverage in the region 350–800 nm. The co-sensitized solar cells based on SPSQ2 + N3 showed the highest short circuit current density of 17.10 mA cm−2, an open circuit voltage of 0.66 V and a fill factor of 0.73, resulting in the highest power conversion efficiency of 8.2%, which is higher than that of the dye-sensitized solar cells based on the individual SPSQ1 and SPSQ2 dyes. The high power conversion efficiency of SPSQ2 + N3 was ascribed to its good light-harvesting properties, which resulted from its broader incident photon current conversion spectrum than that of the individual dyes. The high electron life time and electron recombination, which were the main causes of the higher efficiency of the device, were successfully analysed and correlated using transient absorption spectrometry and intensity-modulated photovoltage spectrometry.
Co-reporter:Towhid H. Chowdhury;A. K. Mahmud Hasan;M. Asri Mat Terdi;Arunakumari M.;Surya Prakash Singh;Md. Khorshed Alam;Idriss M. Bedja;Mohd Hafidz Ruslan;Kamaruzzaman Sopian;Nowshad Amin;Md. Akhtaruzzaman
The Chemical Record 2016 Volume 16( Issue 2) pp:614-632
Publication Date(Web):
DOI:10.1002/tcr.201500206

Abstract

Third-generation solar cells are understood to be the pathway to overcoming the issues and drawbacks of the existing solar cell technologies. Since the introduction of graphene in solar cells, it has been providing attractive properties for the next generation of solar cells. Currently, there are more theoretical predictions rather than practical recognitions in third-generation solar cells. Some of the potential of graphene has been explored in organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs), but it has yet to be fully comprehended in the recent third-generation inorganic–organic hybrid perovskite solar cells. In this review, the diverse role of graphene in third-generation OPVs and DSSCs will be deliberated to provide an insight on the prospects and challenges of graphene in inorganic–organic hybrid perovskite solar cells.

Co-reporter:Hua Jiang, Kazuaki Oniwa, Ashraful Islam, Jian Zhao, Liyuan Han, Ying-Ji Sun, Ming Bao, Naoki Asao, Yoshinori Yamamoto, Tienan Jin
Tetrahedron 2015 Volume 71(Issue 37) pp:6534-6540
Publication Date(Web):16 September 2015
DOI:10.1016/j.tet.2015.04.018
A new series of donor-π-acceptor organic dyes based on thieno[3,2-a]carbazole as a new donor moiety, designated as JH-dyes, has been synthesized for dye-sensitized solar cells (DSCs). The photophysical properties and DSC performances of JH-dyes have been characterized. Among the three JH-dyes, a high power conversion efficiency (η) of 8.04% with a short-circuit current (Jsc) of 14.08 mA cm−2 and an open-circuit voltage (Voc) of 0.78 V has been achieved for DSC based on JH03 bearing hexyl chains on the terthiophene π-linker. The electrochemical impedance spectra (EIS) and intensity-modulated photovoltage spectroscopy (IMVS) of JH-cells were measured to understand the effect of molecular structure on charge transfer process and electron life time.
Co-reporter:Chuanjiang Qin;Antoine Mirloup;Nicolas Leclerc;Ahmed El-Shafei;Liyuan Han;Raymond Ziessel
Advanced Energy Materials 2014 Volume 4( Issue 11) pp:
Publication Date(Web):
DOI:10.1002/aenm.201400085
Co-reporter:Maqbool Hussain, Ashraful Islam, Idriss Bedja, Ravindra Kumar Gupta, Liyuan Han and Ahmed El-Shafei  
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 28) pp:14874-14881
Publication Date(Web):08 May 2014
DOI:10.1039/C4CP00907J
Four novel Ru(II) bipyridyl complexes MH12–15 were synthesized and characterized for dye-sensitized solar cells (DSSCs). Their photovoltaic performance including incident photon-to-current conversion efficiency (IPCE), total solar-to-power conversion efficiency (η%) and ground and excited state oxidation potentials and photoelectrochemical properties were evaluated on mesoporous nanocrystalline TiO2 and compared with the benchmark N719-dye under the same experimental conditions. MH12–15 showed stronger MLCT with significantly higher molar extinction coefficient for the lower energy absorption bands at 553 nm (27500 M−1 cm−1), 554 nm (34605 M−1 cm−1), 577 nm (23300 M−1 cm−1), and 582 nm (39000 M−1 cm−1), respectively, than that of N719 (14200 M−1 cm−1). The introduction of a cyclometallated ligand in dyes MH14 and 15 improved the optical properties and red-shifts of 24 nm and 28 nm, respectively, compared to the non-cyclometallated analogs MH12 and 13. The red shift in the UV-Vis spectra of MH14 and 15 can be attributed to the destabilization of the HOMO t2g of Ru(II). However, the destabilization of the HOMO furnished an upward shift of the ground state oxidation potentials (GSOPs) of MH14 and 15 at −5.44 eV and −5.36 eV against vacuum, respectively, which resulted in a driving force of only 0.22 and 0.16 eV for regeneration of dyes MH14 and 15, respectively. In the case of NCS analogs, MH12 and 13, the GSOPs, however, were −5.56 and −5.51 eV, respectively, which produced a driving force of more than 0.25 eV for dye regeneration. The nanosecond transient absorbance measurements showed that the time needed for the oxidized forms of MH12–MH15 to regenerate the neutral dye is 6 μs, 4 μs, 13 μs and 18 μs, respectively, compared to N719 (2.3 μs). These kinetic data confirmed that the weak thermodynamic force, small negative free energy (−ΔG), for regeneration of MH14 and 15 neutral dyes makes the dye regeneration process kinetically sluggish, which contributed significantly to the loss of both photocurrent and photovoltage. This study clearly elucidated that although cyclometallation may produce significantly better light harvesting, the driving force of less than 0.25 eV is not sufficiently enough for effective dye regeneration.
Co-reporter:Md. Akhtaruzzaman, H.N.M. Ekramul Mahmud, Ashraful Islam, Ahmed Ei Shafei, Mohammed Rezaul Karim, Kamaruzzaman Sopian, Liyuan Han, Yoshinori Yamamoto
Materials Chemistry and Physics 2013 Volume 142(Issue 1) pp:82-86
Publication Date(Web):15 October 2013
DOI:10.1016/j.matchemphys.2013.06.044
•A simple and robust indoline-triphenylamine based sensitizer for DSCs.•An overall conversion efficiency of 6.01% was obtained.•Strong electron donor triphenylamine unit extends absorption spectrum.•Simple and robust molecular design is a promising class of sensitizers.A simple metal-free donor–acceptor type sensitizer U01, bearing strong electron donor indoline-triphenylamine was synthesized for panchromatic sensitization of TiO2 nanocrystalline film. Photovoltaic properties of U01 showed remarkably enhanced light harvesting due to the presence of strong electron donor and robust structure. The new U01 sensitized solar cell exhibited a photovoltaic performance: a short-circuit photocurrent density (Jsc) of 10.70 mA cm−2, an open-circuit photovoltage (Voc) of 0.758 V and a fill factor (FF) of 0.74, corresponding to an overall conversion efficiency of 6.01% under standard global AM 1.5 solar light condition. Our results suggest that indoline-triphenylamine based robust D–A molecular architecture is a highly promising class of panchromatic sensitizers for improvement of the performance of dye-sensitized solar cells (DSCs).A new donor–acceptor type sensitizer, U01 has been synthesized for panchromatic TiO2 sensitization. The photovoltaic properties of U01 showed higher light harvesting compared to D-1 due to the presence of strong electron donor indoline-triphenylamine moiety and compact molecular structure, which translated into a high total conversion efficiency of 6.01%.
Co-reporter:Md. Akhtaruzzaman, Yohei Seya, Naoki Asao, Ashraful Islam, Eunsang Kwon, Ahmed El-Shafei, Liyuan Han and Yoshinori Yamamoto  
Journal of Materials Chemistry A 2012 vol. 22(Issue 21) pp:10771-10778
Publication Date(Web):26 Mar 2012
DOI:10.1039/C2JM30978E
Four novel organic dyes including three based on dibenzosilole (YS01–03) and one based on fluorene (YS04) were synthesized, and their photophysical properties and dye-sensitized solar cell (DSC) performances were characterized. The silicon-containing dibenzosilole-based dyes (YS01–03) were superior to the carbon analogue fluorene-based dye YS04 in incident-photon-to-current conversion efficiency (IPCE), and total solar-to-electric conversion efficiency (η), with YS03, which has the bulkiest and most branched electron donor group, achieving the highest η of 5.07% compared to 2.88% of YS04. To better understand how silicon influences the excited state oxidation potentials (S+/*) and absorption maxima (λmax), the equilibrium molecular geometries of dyes YS01–04 were calculated using density functional theory (DFT) utilizing B3LYP energy functional and DGDZVP basis set. It was shown that the torsion angles (θ1 and θ2) across the biphenyl linkages of dyes containing silicon (YS01–03) were less twisted than that of the silicon-free dye (YS04), which enhanced the π–π* overlap, and that translated into photocurrent enhancements in the silicon-containing dyes YS01–03. Moreover, the vertical electronic excitations and S+/* of dyes YS01–04 were studied using different long-range corrected time-dependent DFT methods, including CAM-B3LYP, LC-BLYP, WB97XD, and LC-wPBE at the basis set level DGDZVP. Excellent agreement between the calculated, using CAM-B3LYP/DGDZVP, and experimental results was found.
Co-reporter:Ahmed El-Shafei, Maqbool Hussain, Aasim Atiq, Ashraful Islam and Liyuan Han  
Journal of Materials Chemistry A 2012 vol. 22(Issue 45) pp:24048-24056
Publication Date(Web):20 Sep 2012
DOI:10.1039/C2JM35267B
Two novel high molar extinction coefficient heteroleptic Ru(II) isomers, NCSU-10 and NCSU-10′, based on carbazole antenna were synthesized with the aid of Knoevenagel reaction, to study the influence of the carbazole antenna and anchoring group (COOH) isomerization on the light harvesting efficiency (LHE), ground and excited state oxidation potentials, incident-photon-to-current conversion efficiency (IPCE), short-circuit photocurrent density (JSC), and total solar-to-electric conversion efficiency (η) for DSSCs, and their device performances were compared to the benchmark dye N719. The photophysical and photoelectrochemical properties discussed herein addressed the significant impact of the carbazole antenna and the position of the anchoring group on JSC and η in DSSCs. Tetrabutylammonium (TBA) substituted NCSU-10 achieved efficient sensitization of nanocrystalline TiO2 over the whole visible range, extending into the near IR region (ca. 870 nm) with an excellent power conversion efficiency (η) of 9.37% under an irradiation of full sunlight (100 mW cm−2) with mask compared to 8.17% of N719 under optimized conditions. NCSU-10 outperformed N719 by 45% in molar absorptivity, 18.8% in JSC, and 14.6% in the total conversion efficiency. Molecular modeling studies (DFT/TD-DFT) of NCSU-10 and NCSU-10′ showed that the HOMO is delocalized not only on Ru and NCS but also on the carbazole with a large coefficient, indicating that the second charge generation transfer in the visible region at ∼400 nm is a mixture of metal-to-ligand charge transfer (MLCT) and strong ligand–ligand charge transfer (LLCT) with a significant HOMO coefficient originating from the carbazole antenna (π) to the bipyridyl electron acceptor (π*). Moreover, DFT calculations showed that the 4,4′-isomer (NCSU-10) is a significantly stronger electron acceptor than the 5,5′-isomer (NCSU-10′), which explained the inferior electron injection and significantly lower JSC of the 5,5′-isomer.
Co-reporter:Ryuji Kaneko, Guohua Wu, Kosuke Sugawa, Joe Otsuki, Ashraful Islam, Liyuan Han, Idriss Bedja, Ravindra Kumar Gupta
Journal of Organometallic Chemistry (15 March 2017) Volume 833() pp:
Publication Date(Web):15 March 2017
DOI:10.1016/j.jorganchem.2017.01.025
•A panchromatic cyclometalated Ru complex is applied for dye-sensitized solar cells.•Absorption tail of this complex extends up to 800 nm.•Deprotonation induces large negative shifts in the redox potentials.•The short-circuit current of cell with our complex is better than that with N719.A cyclometalated ruthenium complex with 6-(ortho-methoxyphenyl)-2,2'-bipyridine (MeO-L) and tricarboxyterpyridine (tpy(CO2H)3) (RuCC·PF6) was prepared, characterized, and evaluated as a dye for dye-sensitized solar cells (DSSCs). The first oxidation and reduction potentials are +0.99 V and −0.81 V vs NHE, respectively. This complex exhibits panchromatic absorption spectrum extending up to 800 nm. The transitions upon visible light excitation were mixtures of metal-to-ligand (Ru → tpy(CO2H)3) and interligand (MeO-L → tpy(CO2H)3) charge transfer transitions. Adsorption of the ruthenium complex on TiO2 was carried out from solutions of RuCC·PF6 in the free acid form or solutions of RuCC·(NBu4)2 in a deprotonated carboxylate form. The DSSC devices employing these complexes as the dye sensitizers generate electricity in response to light over the whole visible range and into the near infrared region over 900 nm. Remarkably, RuCC·(NBu4)2 recorded higher short-circuit current density than a benchmark N719, while the open-circuit voltage was lower, resulting in a modest overall photon-to-current conversion efficiency of 6.4%. The transient absorption and electrochemical impedance spectroscopy have been conducted to get insight into the mechanistic details of the DSSC cells, which suggested that the presence of NBu4 cation was beneficial in retarding the unwanted recombination reaction. Considering the efficient charge injection and regeneration as manifested by the large short-circuit current, modification based on the present structure would be a promising strategy toward higher efficiency dyes for DSSCs.A new cyclometalated ruthenium dye has been prepared, characterized, and applied to dye-sensitized solar cells (DSSCs). The short-circuit photocurrent density of DSSCs using this complex as the sensitizer dye exceeded that of the benchmark dye N719 under the same conditions because of the near IR sensitivity.
Co-reporter:Lingamallu Giribabu, Naresh Duvva, Surya Prakash Singh, Liyuan Han, Idriss M. Bedja, Ravindra Kumar Gupta and Ashraful Islam
Inorganic Chemistry Frontiers 2017 - vol. 1(Issue 3) pp:NaN467-467
Publication Date(Web):2016/08/15
DOI:10.1039/C6QM00070C
Two new metal-free organic sensitizers have been designed based on tetrathiafulvalene scaffolds by implementing a donor–π–acceptor (D–π–A) approach in which thioalkyl substituted tetrathiafulvalene acts as a donor, substituted anthracene as a π-spacer and cyanoacrylic acid acts as an acceptor as well as an anchoring group. Spectroscopic, electrochemical and DFT studies confirmed the molecular integrity of both sensitizers. The onset of absorption of both sensitizers extends up to 600 nm in solution and up to 700 nm on nanocrystalline TiO2. DFT studies specified that the HOMO is delocalized over the anthracene as well as the dithiole units, and the LUMO is delocalized over the anchoring group in both sensitizers. The new sensitizers have shown an improved efficiency of 7.15% in dye-sensitized solar cells using an I−/I3− redox couple. The enhanced efficiency might be due to the thioalkyl group wrapping over the anthracene π-spacer to prevent the recombination of electrons in the TiO2 conduction band. Recombination studies indicate the regeneration of the oxidized dye due to the redox couple.
Co-reporter:Jian Zhao, Kazuaki Oniwa, Ashraful Islam, Chuanjiang Qin, Naoki Asao, Liyuan Han, Yoshinori Yamamoto and Tienan Jin
Inorganic Chemistry Frontiers 2015 - vol. 2(Issue 3) pp:NaN258-258
Publication Date(Web):2015/01/20
DOI:10.1039/C4QO00285G
A new series of donor–π-acceptor organic K-dyes based on the thieno[2,3,a]carbazole moiety as a new electron donor, trithiophene as a π-linker and cyanoacrylic acid as an electron acceptor were designed and synthesized for achieving high performances in dye-sensitized solar cells (DSCs). The substituent effect and the molecular planarity for photophysical properties and DSC performances of K-dyes have been investigated, and the highest power conversion efficiency of 7.4% has been achieved. EIS and IMVS were employed to study the effect of the molecular structure on the charge transfer process and electron lifetime.
Co-reporter:Md. Akhtaruzzaman, Yohei Seya, Naoki Asao, Ashraful Islam, Eunsang Kwon, Ahmed El-Shafei, Liyuan Han and Yoshinori Yamamoto
Journal of Materials Chemistry A 2012 - vol. 22(Issue 21) pp:NaN10778-10778
Publication Date(Web):2012/03/26
DOI:10.1039/C2JM30978E
Four novel organic dyes including three based on dibenzosilole (YS01–03) and one based on fluorene (YS04) were synthesized, and their photophysical properties and dye-sensitized solar cell (DSC) performances were characterized. The silicon-containing dibenzosilole-based dyes (YS01–03) were superior to the carbon analogue fluorene-based dye YS04 in incident-photon-to-current conversion efficiency (IPCE), and total solar-to-electric conversion efficiency (η), with YS03, which has the bulkiest and most branched electron donor group, achieving the highest η of 5.07% compared to 2.88% of YS04. To better understand how silicon influences the excited state oxidation potentials (S+/*) and absorption maxima (λmax), the equilibrium molecular geometries of dyes YS01–04 were calculated using density functional theory (DFT) utilizing B3LYP energy functional and DGDZVP basis set. It was shown that the torsion angles (θ1 and θ2) across the biphenyl linkages of dyes containing silicon (YS01–03) were less twisted than that of the silicon-free dye (YS04), which enhanced the π–π* overlap, and that translated into photocurrent enhancements in the silicon-containing dyes YS01–03. Moreover, the vertical electronic excitations and S+/* of dyes YS01–04 were studied using different long-range corrected time-dependent DFT methods, including CAM-B3LYP, LC-BLYP, WB97XD, and LC-wPBE at the basis set level DGDZVP. Excellent agreement between the calculated, using CAM-B3LYP/DGDZVP, and experimental results was found.
Co-reporter:Ahmed El-Shafei, Maqbool Hussain, Aasim Atiq, Ashraful Islam and Liyuan Han
Journal of Materials Chemistry A 2012 - vol. 22(Issue 45) pp:NaN24056-24056
Publication Date(Web):2012/09/20
DOI:10.1039/C2JM35267B
Two novel high molar extinction coefficient heteroleptic Ru(II) isomers, NCSU-10 and NCSU-10′, based on carbazole antenna were synthesized with the aid of Knoevenagel reaction, to study the influence of the carbazole antenna and anchoring group (COOH) isomerization on the light harvesting efficiency (LHE), ground and excited state oxidation potentials, incident-photon-to-current conversion efficiency (IPCE), short-circuit photocurrent density (JSC), and total solar-to-electric conversion efficiency (η) for DSSCs, and their device performances were compared to the benchmark dye N719. The photophysical and photoelectrochemical properties discussed herein addressed the significant impact of the carbazole antenna and the position of the anchoring group on JSC and η in DSSCs. Tetrabutylammonium (TBA) substituted NCSU-10 achieved efficient sensitization of nanocrystalline TiO2 over the whole visible range, extending into the near IR region (ca. 870 nm) with an excellent power conversion efficiency (η) of 9.37% under an irradiation of full sunlight (100 mW cm−2) with mask compared to 8.17% of N719 under optimized conditions. NCSU-10 outperformed N719 by 45% in molar absorptivity, 18.8% in JSC, and 14.6% in the total conversion efficiency. Molecular modeling studies (DFT/TD-DFT) of NCSU-10 and NCSU-10′ showed that the HOMO is delocalized not only on Ru and NCS but also on the carbazole with a large coefficient, indicating that the second charge generation transfer in the visible region at ∼400 nm is a mixture of metal-to-ligand charge transfer (MLCT) and strong ligand–ligand charge transfer (LLCT) with a significant HOMO coefficient originating from the carbazole antenna (π) to the bipyridyl electron acceptor (π*). Moreover, DFT calculations showed that the 4,4′-isomer (NCSU-10) is a significantly stronger electron acceptor than the 5,5′-isomer (NCSU-10′), which explained the inferior electron injection and significantly lower JSC of the 5,5′-isomer.
Co-reporter:G. Hanumantha Rao, A. Venkateswararao, L. Giribabu, Liyuan Han, Idriss Bedja, Ravindra Kumar Gupta, Ashraful Islam and Surya Prakash Singh
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 21) pp:NaN14285-14285
Publication Date(Web):2016/04/19
DOI:10.1039/C6CP01669C
A combination of squaraine-based dyes (SPSQ1 and SPSQ2) and a ruthenium-based dye (N3) were chosen as co-sensitizers to construct efficient dye-sensitized solar cells. The co-sensitization of squaraine dyes with N3 enhanced their light-harvesting properties as a result of the broad spectral coverage in the region 350–800 nm. The co-sensitized solar cells based on SPSQ2 + N3 showed the highest short circuit current density of 17.10 mA cm−2, an open circuit voltage of 0.66 V and a fill factor of 0.73, resulting in the highest power conversion efficiency of 8.2%, which is higher than that of the dye-sensitized solar cells based on the individual SPSQ1 and SPSQ2 dyes. The high power conversion efficiency of SPSQ2 + N3 was ascribed to its good light-harvesting properties, which resulted from its broader incident photon current conversion spectrum than that of the individual dyes. The high electron life time and electron recombination, which were the main causes of the higher efficiency of the device, were successfully analysed and correlated using transient absorption spectrometry and intensity-modulated photovoltage spectrometry.
Co-reporter:Maqbool Hussain;Idriss Bedja;Ravindra Kumar Gupta;Liyuan Han;Ahmed El-Shafei
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 28) pp:NaN14881-14881
Publication Date(Web):2014/06/25
DOI:10.1039/C4CP00907J
Four novel Ru(II) bipyridyl complexes MH12–15 were synthesized and characterized for dye-sensitized solar cells (DSSCs). Their photovoltaic performance including incident photon-to-current conversion efficiency (IPCE), total solar-to-power conversion efficiency (η%) and ground and excited state oxidation potentials and photoelectrochemical properties were evaluated on mesoporous nanocrystalline TiO2 and compared with the benchmark N719-dye under the same experimental conditions. MH12–15 showed stronger MLCT with significantly higher molar extinction coefficient for the lower energy absorption bands at 553 nm (27 500 M−1 cm−1), 554 nm (34 605 M−1 cm−1), 577 nm (23 300 M−1 cm−1), and 582 nm (39 000 M−1 cm−1), respectively, than that of N719 (14 200 M−1 cm−1). The introduction of a cyclometallated ligand in dyes MH14 and 15 improved the optical properties and red-shifts of 24 nm and 28 nm, respectively, compared to the non-cyclometallated analogs MH12 and 13. The red shift in the UV-Vis spectra of MH14 and 15 can be attributed to the destabilization of the HOMO t2g of Ru(II). However, the destabilization of the HOMO furnished an upward shift of the ground state oxidation potentials (GSOPs) of MH14 and 15 at −5.44 eV and −5.36 eV against vacuum, respectively, which resulted in a driving force of only 0.22 and 0.16 eV for regeneration of dyes MH14 and 15, respectively. In the case of NCS analogs, MH12 and 13, the GSOPs, however, were −5.56 and −5.51 eV, respectively, which produced a driving force of more than 0.25 eV for dye regeneration. The nanosecond transient absorbance measurements showed that the time needed for the oxidized forms of MH12–MH15 to regenerate the neutral dye is 6 μs, 4 μs, 13 μs and 18 μs, respectively, compared to N719 (2.3 μs). These kinetic data confirmed that the weak thermodynamic force, small negative free energy (−ΔG), for regeneration of MH14 and 15 neutral dyes makes the dye regeneration process kinetically sluggish, which contributed significantly to the loss of both photocurrent and photovoltage. This study clearly elucidated that although cyclometallation may produce significantly better light harvesting, the driving force of less than 0.25 eV is not sufficiently enough for effective dye regeneration.
Formamide, N,N-dimethyl-
3H-Indolium, 2,3,3-trimethyl-1-octyl-, iodide
ACETONITRILE
Benzenamine, 4-bromo-N,N-dibutyl-
Pyridine,2-(trimethylstannyl)-
2-Propenoic acid, 2-cyano-3-[5'''-(9-ethyl-9H-carbazol-3-yl)-3',3'',3''',4-tetrahexyl[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl]-
9-Phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole
(E)-4-((5-carboxy-3,3-dimethyl-1-octyl-3H-indolium-2-yl)methylene)-2-((E)-(1-ethyl-3,3-dimethylindolin-2-ylidene)methyl)-3-oxocyclobut-1-enolate
3H-Indolium, 5-carboxy-2,3,3-trimethyl-1-octyl-, iodide (1:1)
N2,N2,N2',N2',N7,N7,N7',N7'-Octakis(4-methoxyphenyl)-9,9'-spirobi[fluorene]-2,2',7,7'-tetraamine