Faculty Publications
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Item Molecular Engineering and Theoretical Investigation of Novel Metal-Free Organic Chromophores for Dye-Sensitized Solar Cells(Elsevier Ltd, 2015) Babu, D.D.; Cheema, H.; Elsherbiny, D.; El-Shafei, A.; Vasudeva Adhikari, A.V.In this work we report design and synthesis of three new metal free D-D-A-?-A type dyes (E1-3) with different acceptor/anchoring groups, as effective sensitizers for nanocrystalline titanium dioxide based dye sensitized solar cells. All the three dyes carry electron donating methoxy group as an auxiliary and indole as a principal donor, cyanovinylene as an auxiliary acceptor and thiophene as a ?-spacer. Whereas, cyanoacetic acid, rhodanine-3-acetic acid and 4-aminobenzoic acid perform as acceptor/anchoring moieties, respectively in the dyes E1-3. Though the dye containing 4-aminobenzoic acid unit (E3) exhibits comparatively lower ?max, it shows the highest power conversion efficiency arising from the higher electron life time and good light-harvesting capability. The DFT studies reveal a better charge separation between the HOMO and LUMO levels of E3, further substantiating the experimental results. Among the three dyes, E3 shows the best photovoltaic performance with short-circuit current density (Jsc) of 9.35 mA cm-2, open-circuit voltage (Voc) of 620 mV and fill factor (FF) of 0.71, corresponding to an overall conversion efficiency of 4.12% under standard global AM 1.5G. © 2015 Elsevier Ltd. All rights reserved.Item New indole based co-sensitizers for dye sensitized solar cells exceeding 10% efficiency(Royal Society of Chemistry, 2016) Babu, D.D.; Su, R.; El-Shafei, A.; Vasudeva Adhikari, A.V.In this work, we report the molecular engineering and synthesis of three novel indole co-sensitizers DBA-3, DBA-4 and DBA-5 with D–D–A (donor–donor–acceptor) architecture. In the quest to comprehend the role of auxiliary donors on co-sensitization, we have incorporated auxiliary electron donating moieties with varying geometries and electron donating capabilities to the indole moiety in order to obtain the aforementioned co-sensitizers. Their electrochemical and photo-physical properties along with molecular geometries, obtained from Density Functional Theory (DFT) are studied to vindicate the effect of the co-sensitizer structures on the photovoltaic properties of DSSCs. Furthermore, for the first time we demonstrate the profound effect of auxiliary donor groups on the co-sensitization performance of the organic molecules. Devices co-sensitized using DBA-3, DBA-4 and DBA-5 along with ruthenium sensitizer NCSU-10, displayed significantly different photovoltaic conversion efficiencies (PCEs) when compared to that of the device sensitized using only NCSU-10. The photovoltaic and EIS studies revealed that, the co-sensitizer DBA-4 succeeded in enhancing the light harvesting capability as well as efficiently suppressing undesirable charge recombinations in the cell. Due to the aforementioned reasons, a cell co-sensitized using DBA-4 has shown promising photovoltaic results and exhibited an enhanced overall efficiency of 10.12%. Furthermore, vertical electronic excitations, calculated using TD-DFT, are in good agreement with the experimental l max results, which clearly indicates that, the energy functional and basis set utilized in this study can be effectively employed for predicting the absorption spectra of novel photosensitizers, with high confidence prior to their synthesis. All these results provide a better understanding and deeper insight into the intricacies involved in the design of superior co-sensitizers to further improve the performance of DSSCs. This journal is © The Royal Society of Chemistry 2016Item From Molecular Design to Co-sensitization; High performance indole based photosensitizers for dye-sensitized solar cells(Elsevier Ltd, 2016) Babu, D.D.; Su, R.; El-Shafei, A.; Vasudeva Adhikari, A.V.Herein, we report the molecular design and synthesis of two novel organic co-adsorbers DBA-1((Z)-2-cyano-3-(5-(4-(cyclohexa-1,5-dien-3-ynyl(phenyl)amino)phenyl)-1-hexyl-1H-indol-3-yl)acrylic acid) and (DBA-2) 5-((5-(4-(diphenylamino)phenyl)-1-hexyl-1H-indol-3-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)-trione with D-D-A (donor-donor-acceptor) architecture. We have combined the strong electron donating triphenylamine group with indole moiety attached to different acceptors/anchoring groups, as co-adsorbers for dye-sensitized solar cells and we present for the first time, the role of anchoring/acceptor unit on their co-adsorption properties. In this study, cyanoacetic acid and barbituric acid are employed as anchoring groups in the co-sensitizers DBA-1 and DBA-2, respectively. Their electrochemical and photo-physical properties along with molecular geometries, obtained from Density Functional Theory (DFT) are employed to vindicate the effect of co-sensitizer structures on photovoltaic properties of DSSCs. We have demonstrated that the co-sensitization effect is profoundly dependent upon the anchoring/acceptor unit in the co-adsorber molecule. Devices co-sensitized using DBA-1 and DBA-2 along with HD-2 (Ru-complex of 4, 4?-bis-(1,4-benzodioxan-5-yl-vinyl)-[2,2?]bipyridine), displayed higher power conversion efficiencies (PCEs) than the device sensitized using only HD-2. In the present work, ruthenium based sensitizer, HD-2, has been chosen due to its better solar-to-power conversion efficiency and impressively higher photocurrent densities than that of standard N719. Among them, co-adsorber DBA-2, containing barbituric acid as the acceptor/anchoring group displays promising photovoltaic results and exhibited an enhanced efficiency of 8.06%. Further, good agreement between the calculated and experimental results showcase the precision of the energy functional and basis set utilized in this study. All these findings provide a deeper insight and better understanding into the intricacies involved in the design of superior co-sensitizers for development of highly efficient DSSCs. © 2016 Elsevier Ltd. All rights reserved.Item Highly efficient panchromatic dye-sensitized solar cells: Synergistic interaction of ruthenium sensitizer with novel co-sensitizers carrying different acceptor units(Elsevier Ltd, 2016) Babu, D.D.; Elsherbiny, D.; Cheema, H.; El-Shafei, A.; Vasudeva Adhikari, A.V.Herein, we report the molecular design, synthesis and photovoltaic performance studies of three new organic co-sensitizers, N1-3 carrying indole and thiophene units linked to different acceptors/anchoring groups, as co-adsorbents for dye sensitized solar cells. We present the role of anchoring/acceptor units on co-sensitization properties N1-3. Their photo-physical and electrochemical results along with molecular geometry, obtained from Density Functional Theory are utilized to rationalize the influence of co-sensitizer structures on photovoltaic properties for DSSCs. We have shown that, the co-sensitization effect is profoundly dependent upon the anchoring/acceptor unit in the co-adsorbents. Among them, N3 containing 4-aminobenzoic acid shows promising co-sensitization results and exhibits an enhanced efficiency of 9.26%, when co-sensitized with a ruthenium dye, HD-14. Further, the study highlights the importance of molecular matching between the sensitizer and co-sensitizer in enhancing the efficiency. Furthermore, vertical electronic excitations are calculated using time dependent density functional theory studies. © 2016 Elsevier Ltd. All rights reserved.Item Synthesis and photovoltaic performance of a novel asymmetric dual-channel co-sensitizer for dye-sensitized solar cell beyond 10% efficiency(Elsevier Ltd, 2017) Babu, D.D.; Su, R.; Naik, P.; El-Shafei, A.; Vasudeva Adhikari, A.V.In this paper, we report the design and synthesis of a new bi-anchoring indole based co-sensitizer DBA-8 with A-?-D-A (acceptor-? bridge-donor-acceptor) architecture, carrying indole moiety as a donor and barbituric acid as acceptor/anchoring groups. Its photo-physical and electrochemical properties along with molecular geometries, calculated from Density Functional Theory (DFT) are employed to comprehend the effect of co-sensitizer structure on photovoltaic characteristics of DSSCs. The abovementioned organic dye (DBA-8) was employed as a co-sensitizer along with well-known ruthenium based sensitizer NCSU-10 in order to broaden the spectral responses of the co-sensitized DSSC. In the present work, for the first time we are demonstrating the profound role of a dual-anchoring co-sensitizer that can play in ameliorating the overall performance of a solar cell. The photovoltaic studies indicated that, the co-sensitizer DBA-8 succeeded in increasing the light harvesting ability in the device significantly. Notably, the device co-sensitized using 0.2 mM DBA-8 along with ruthenium based chromophore NCSU-10, showed a maximum efficiency of 10.68% (Jsc = 25.14 mAcm?2, Voc = 0.695 V, ff = 61.2%). Further, the good agreement between the theoretically and experimentally obtained ?max data vindicate that, the energy functional and basis set employed in this study can be successfully utilized for predicting the absorption spectra of new photosensitizers, with great precision before synthesis. Furthermore, all these findings showcase the vast potential of bi-anchoring molecules in improving the overall performance of the dye-sensitized solar cells. © 2017 Elsevier LtdItem New carbazole based dyes as effective co-sensitizers for DSSCs sensitized with ruthenium (II) complex (NCSU-10)(Elsevier B.V., 2018) Naik, P.; Su, R.; Elmorsy, M.R.; El-Shafei, A.; Vasudeva Adhikari, A.V.Herein, we report the design and synthesis of three new D–A type metal-free carbazole based dyes (S1–3) as effective co-sensitizers for dye-sensitized solar cell (DSSC) sensitized with Ru(II) complex (NCSU-10). In this new design, the electron rich carbazole unit was attached to three different electron withdrawing/anchoring species, viz. 4-amino benzoic acid, sulfanilic acid and barbituric acid. The dyes were characterized by spectral, photophysical and electrochemical analysis. Their optical and electrochemical parameters along with molecular geometries, optimized from DFT have been employed to apprehend the effect of the structures of these co-sensitizers on the photovoltaic performances. Further, S1–3 dyes were co-sensitized along with a well-known NCSU-10 dye in order to broaden the spectral response of the co-sensitized devices and hence improve the efficiency. The photovoltaic performance studies indicated that, the device fabricated using S1 dye as co-sensitizer with 0.2 mM of NCSU-10 exhibited improved PCE of 9.55% with JSC of 22.85 mA cm?2, VOC of 0.672 V and FF of 62.2%, whereas the DSSC fabricated with dye NCSU-10 (0.2 mM) alone displayed PCE of 8.25% with JSC of 20.41 mA cm?2, VOC of 0.667 V and FF of 60.6%. Furthermore, electronic excitations simulated using time-dependent DFT, were in good agreement with the experimentally obtained results of the co-sensitizers, indicating that the exchange-correlation function and basis set utilized for predicting the spectra of the co-sensitizers are quite appropriate for the calculations. In conclusion, the results showed the potential of simple organic co-sensitizers in the development of efficient DSSCs. © 2017 Science PressItem Simple diphenylamine based D-?-A type sensitizers/co-sensitizers for DSSCs: A comprehensive study on the impact of anchoring groups(Royal Society of Chemistry, 2019) Kesavan, R.; Abdellah, I.M.; Singh, S.P.; El-Shafei, A.; Vasudeva Adhikari, A.V.Herein, we report the design, synthesis and characterization of a new series of simple donor-? spacer-acceptor/anchor (D-?-A) type diphenylamine based metal-free organic dyes possessing three different anchoring groups, viz. 4-aminobenzoic acid (DTP), 2-(4-nitrophenyl)acetonitrile (DTN), and barbituric acid (DTB), connected with 2-(thiophene-2-yl)-acetonitrile, as effective sensitizers and co-sensitizers in Dye Sensitized Solar Cells (DSSCs). They were subjected to photophysical, electrochemical and theoretical studies. The dyes exhibited characteristic ?abs and ?emi in the range of 445-485 and 545-570 nm, respectively. Both optical and electrochemical band gaps were found to be in the range of 2.2 to 2.35 eV. The driving forces for injection (?Ginj), recombination (?Grec) and regeneration (?Greg) processes were evaluated to understand their feasibility. Finally, the DSSC devices were fabricated employing the new dyes as sensitizers as well as co-sensitizers along with the Ru(ii) based N3 dye. Interestingly, DTP carrying 4-aminobenzoic acid as the anchoring group shows the best photoelectrochemical performance, viz. photovoltaic conversion efficiency (PCE) = 4.4%, open circuit potential (VOC) = 0.577 V, and short-circuit current density (JSC) = 9.06 mA cm-2 with a broad incident photon conversion efficiency (IPCE) spectrum. Co-sensitization of the dyes brought about enhanced VOC values, compared to the N3 dye alone. Finally, different interface resistance values obtained from the electrochemical impedance spectroscopy (EIS) circuit fitting were used to study the fundamental processes of energy conversion. © 2019 the Owner Societies.Item Asymmetric Dual Anchoring Sensitizers/Cosensitizers for Dye Sensitized Solar Cell Application: An Insight into Various Fundamental Processes inside the Cell(American Chemical Society service@acs.org, 2019) Kesavan, R.; Attia, F.; Su, R.; Anees, P.; El-Shafei, A.; Vasudeva Adhikari, A.V.To study the various fundamental processes occurring inside the dye sensitized solar cell (DSSC), we have fabricated devices employing newly synthesized diphenylamine-based organic dyes with A-D-?-A configuration, carrying four different anchoring groups, namely, cyanoacetic acid (DDC), rhodanine acetic acid (DDR), 4-hydrazinylbenzoic acid (DDH), and barbituric acid (DDB), as effective sensitizers/cosensitizers. In the present work, all the bianchoring dyes were subjected to photophysical, electrochemical, thermodynamic, photoelectrochemical, and theoretical studies. All of them displayed characteristic ?abs and ?emi in the range of 415-480 and 570-680 nm, respectively. Their optical and electrochemical band gaps were calculated to be in the order of 2.1 to 2.3 eV. The calculated driving forces for electron injection (?Ginj), recombination (?Ginj), and regeneration (?Greg) processes were found to be negative, showing the feasibility of these processes, while their DFT studies clearly indicated the directional flow of electrons within the dye in the cell. The devices with DDC as sensitizer displayed the highest conversion efficiency of 2.53%, whereas DDB exhibited the maximum of 7.69% when employed as a cosensitizer along with Ru (II) based HD-2 dye. Finally, EIS circuit fitting was carried out in order to obtain different interface resistance values to study the fundamental processes of energy conversion. © © 2019 American Chemical Society.