@article {44642, title = {Fused fluorenylindolenine-donor-based unsymmetrical squaraine dyes for dye-sensitized solar cells}, journal = {ACS Applied Materials \& Interfaces}, volume = {10}, year = {2018}, month = {AUG}, pages = {26335-26347}, abstract = {

A series of four unsymmetrical squaraine dyes, XSQ1-4, were synthesized using a fused fluorenylindolenine-based donor unit for dye-sensitized solar cells (DSSCs). The fused structure of fluorenylindolenine helped in moving the absorption toward the near-infrared (NIR) region, and the two sp(3)-C centers available on this donor were utilized to incorporate out-of-plane alkyl chains in opposite directions to control the dye-dye interactions on the TiO2 surface. High extinction coefficient (epsilon \>= 10(5) M-1 cm(-1)) for absorbing NIR photons and suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels with respect to the conduction band of TiO2 and electrolyte for charge injection and dye regeneration processes, respectively, make these dyes potential sensitizers for DSSCs. Introduction of branched alkyl groups in the pi-framework helped in controlling dye aggregation to reduce exciton quenching and assisted in TiO2 surface passivation to avoid the charge recombination process. Furthermore, having a naphthyl group on the indole part of the anchoring group containing segment helped to red-shift the absorption spectrum of dyes 15 nm toward the NIR region (XSQ3-4). Among all of the dyes under investigation, XSQ2 gave the best photovoltaic performance, having a short-circuit current density (J(SC)) of 13.99 mA cm(-2), open -circuit voltage (V-OC) of 0.66 V, and a fill factor (ff) of 0.71, with a device performance (eta) of 6.57\%. Electrochemical impedance spectroscopy revealed higher electron lifetime on TiO2 for XSQ2, which helps to avoid the charge recombination process.

}, keywords = {Dye-sensitized solar cells, fluorenylindolenine, H- and J-type aggregation, NIR absorption, out-of-plane alkyl groups, squaraine dyes}, issn = {1944-8244}, doi = {10.1021/acsami.8b09866}, author = {Bisht, Rajesh and Sudhakar, Vediappan and Kavungathodi, Munavvar Fairoos Mele and Karjule, Neeta and Nithyanandhan, Jayaraj} } @article {47381, title = {D-A-D based complementary unsymmetrical squaraine dyes for co-sensitized solar cells: enhanced photocurrent generation and suppressed charge recombination processes by controlled aggregation}, journal = {ACS Applied Energy Materials}, volume = {4}, year = {2021}, month = {APR}, pages = {3182-3193}, type = {Article}, abstract = {

A series of donor-acceptor-donor (D-A-D) based unsymmetrical squaraine dyes have been synthesized with indoline and aniline as donor units. The sp(3)-C, N atoms of the indoline and N atom of the aniline donors are appended with alkyl groups systematically to control the self-assembly of dyes on TiO2 and to passivate the photoanode that helps in improving the open circuit voltage (V-oc) of the dye-sensitized solar cell (DSSC) device. The resulting dyes, AK1-4, possess strong absorptions between 529 and 541 nm with extinction coefficients of 1.44-1.84 X 10(5) M-1 cm(-1). Photophysical and electrochemical studies revealed that the lowest unoccupied molecular orbital and highest occupied molecular orbital of the dyes are aligned with the conduction band of TiO2 and the redox function of the electrolyte for the efficient charge injection and dye regeneration processes, respectively. A DSSC device performance for AK4 of 7.93\% (V-oc of 815.88 mV and short circuit current density (J(sc)) of 12.4 mA/cm(2)) is obtained, with an incident photon to current conversion efficiency (IPCE) response of 92\% at 473 nm and 86\% at 566 nm without sensitizing with coadsorbent. IPCE studies revealed the equal contribution for the photocurrent generation from the H-aggregated structures. Further, such a high V-oc and DSSC efficiency have been observed first time for this class of zwitterionic dyes with the I-/I-3(-) electrolyte without sensitizing with coadsorbent. The importance of introducing the alkyl groups at the indoline as well as aniline donor units for the synergistic boosting of both V-oc, and J(sc) is compared with the model dye AK1. Complementary light absorbing dyes SQ1 and SQS4 possess absorption at 643 nm with extinction coefficients of 1.4 and 3.0 x 10(5) M-1 cm(-1), respectively. A cosensitized device performance of 9.36\% is obtained for the AK4:SQS4 (1:1) combination in the I-/I-3(-) electrolyte. The IPCE profile indicates a good response over 450-700 nm with 94\% at 621 nm. The importance of aggregated structures from both the dyes AK4 and SQS4 for photocurrent generation is realized.

}, keywords = {aggregation of dyes, co-sensitization, extension of conjugation, H-aggregate, squaraine dyes}, issn = {2574-0962}, doi = {10.1021/acsaem.0c02966}, author = {Singh, Ambarish Kumar and Veetil, Athulya Nellur and Nithyanandhan, Jayaraj} } @article {48746, title = {Visible-light-active unsymmetrical squaraine dyes with 1 V of open-circuit voltage for dye-sensitized solar cells}, journal = {ChemPhotoChem}, volume = {7}, year = {2023}, month = {MAY}, type = {Article}, abstract = {

A series of alkyl-group-functionalized, aniline- and indoline-donor-based, unsymmetrical visible-light-active squaraine dyes, AM1-3, were designed and synthesized. Dye-sensitized solar cell (DSSC) devices were fabricated with both I-/I-3(-) and [Cu(tmby)(2)](+/2+) electrolytes. DSSC devices sensitized with the AM1 and AM2 dyes showed relatively high-power conversion efficiency of 7.44 \% and 7.22 \%, respectively with I-/I-3(-) in the absence of chenodeoxycholic acid (CDCA) than those of the AM3 dye (5.41 \%). The [Cu(tmby)(2)](+/2+) electrolyte along with poly(3,4-ethylenedioxythiophene) (PEDOT) as cathode material showed excellent open-circuit potentials (V-OC) of 1030, 1025, and 1001 mV with the DSSC efficiency of 8.05 \%, 7.96 \%, and 5.84 \%, respectively, for the AM1, AM2, and AM3 dyes in the absence of CDCA. Here, the AM1 dye exhibited the maximum DSSC efficiency of 8.05 \% and V-OC of 1030 mV, which is the highest obtained efficiency and V-OC for the visible-light active zwitterionic unsymmetrical-squaraine dye with copper-based electrolyte.

}, keywords = {Cu electrolytes, dihedral angle, Dye-sensitized solar cells, open circuit voltage, squaraine dyes}, issn = {2367-0932}, doi = {10.1002/cptc.202200328}, author = {Singh, Amrita and Kumar Singh, Ambarish and Dixit, Ruchi and Vanka, Kumar and Krishnamoorthy, Kothandam and Nithyanandhan, Jayaraj} } @article {49283, title = {Triazatruxene amine donor-based visible-light-responsive unsymmetrical squaraine dyes for dye-sensitized solar cells}, journal = {ACS Applied Energy Materials}, volume = {7}, year = {2024}, month = {SEP}, pages = {7982-7991}, type = {Article}, abstract = {

Optimized charge-transfer dynamics at the dye-TiO2/electrolyte interface are required for an enhanced dye-sensitized solar cell (DSSC) device performance. Such an optimized interface enhances the charge-injection, dye-regeneration, and diminished charge-recombination processes, synergistically enhancing the device efficiency. In this study, octupolar-structured sensitizers are designed to improve the interaction between the dye and the redox electrolyte for increasing the dye-regeneration process upon photoexcitation. Accordingly, a set of unsymmetrical squaraine dyes with indoline and triazatruxene amine donor-based D-A-D dyes are designed (KV1-KV3), synthesized, and sensitized with a semiconducting metal oxide (TiO2) film. The sensitizer forms a monolayer on the TiO2 surface, leading to a dye-dye interaction, which broadens the absorption spectrum. The N atom of the triazatruxene amine donor was left unsubstituted in KV1, whereas a hexyl chain was installed in KV2 and KV3 and a branched alkyl chain was installed on the core N atoms in KV3 to control the self-assembly of dyes on the TiO2 surface. Self-assembly of alkyl groups wrapped in KV1-KV3 dyes on the TiO2 surface aids surface passivation and broadens the absorption profile, improving the light-harvesting capabilities. The DSSC devices based on KV2 exhibited a high power conversion efficiency of 7.85\% (V-oc = 794 mV, J(sc) = 14.76 mA/cm(2), and FF = 67\%), with an onset incident photon-to-current conversion efficiency response from 680 nm.

}, keywords = {aggregationof dyes, Dye-sensitized solar cells, metal-free organic dyes, self-assembly of dye, squaraine dyes, triazatruxene}, issn = {2574-0962}, doi = {10.1021/acsaem.4c01591}, author = {Ingole, Kiran Balaso and Deshmukh, Shivdeep Suresh and Verma, Tushar Singh and Krishnamurty, Sailaja and Krishnamoorthy, Kothandam and Nithyanandhan, Jayaraj} } @article {49031, title = {Visible, far-red, and near-infrared active unsymmetrical squaraine dyes based on extended conjugation within the polymethine framework for dye-sensitized solar cells}, journal = {ACS Applied Energy Materials}, volume = {7}, year = {2024}, month = {FEB }, pages = {1461-1475}, type = {Article}, abstract = {

Alkyl group wrapped visible, far-red, and NIR active unsymmetrical squaraine dyes with pi-extension in the polymethine framework-based AM4-AM7 have been designed, synthesized, and utilized as sensitizers for dye-sensitized solar cells. To extend the pi-conjugation within the polymethine framework, thiophene moieties have been incorporated between the donor and acceptor moieties. Absorption spectroscopic studies revealed that pi-extension with each -C \& boxH;C- unit resulted similar to 100 nm of redshift in the charge transfer transition with the lambda(maximum) of 541, 643, 747, and 833 nm for AM4, AM5, AM6, and AM7 dyes, respectively, with the molar extinction coefficient of \>10(5) M(-1)cm(-1). The pi-extended conjugation-based AM6 and AM7 dyes showed improved light-harvesting efficiency (LHE), where the AM7 dye showed an LHE of 386 nm at 60\%. Electrochemical studies of AM dyes revealed that the HOMO energy level of the sensitizers has been modulated systematically. Further, pi-extension within the polymethine framework showed a dramatic effect on V-OC, J(SC), and device efficiency when move from visible active AM4 to far-red active to NIR active AM7 dyes. The DSSC efficiencies of 7.35, 5.18, 0.08, and 0.053\% have been achieved with the I-/I-3(-) electrolyte (Z-50) for the AM4, AM5, AM6, and AM7 dyes, respectively. Further, AM4 dye has been cosensitized with AM5, AM6, and AM7 dyes, where AM4:AM5 (1:1) composition achieved the maximum efficiency of 8.12\% with I-/I-3(-) electrolyte (Z-50) compared to the other cosensitization compositions.

}, keywords = {aggregation of dyes, DSSC device efficiency, light-harvesting efficiency, pi-extension, polymethine framework, squaraine dyes}, issn = {2574-0962}, doi = {10.1021/acsaem.3c02610}, author = {Singh, Amrita and Singh, Ambarish Kumar and Dixit, Ruchi and Vanka, Kumar and Krishnamoorthy, Kothandam and Nithyanandhan, Jayaraj} } @article {49614, title = {Double anchoring squaraine dye with triazatruxene amine donor for dye-sensitized solar cells: sequential cosensitization for panchromatic light-harvesting}, journal = {Journal of Photochemistry and Photobiology A-Chemistry}, volume = {462}, year = {2025}, month = {MAY}, pages = {116229}, type = {Article}, abstract = {

Dyes are firmly bound to a semiconducting TiO2 film using carboxylic acid anchoring groups for an efficient electron transfer from the excited state of dye to the conduction band (CB) of TiO2. Strong dye binding can be accomplished with multi-anchoring dye designs to improve photophysical characteristics, including high extinction coefficients, panchromatic absorption, post-sensitization modifications, and dark current suppression, besides enhancing the stability of the dye-TiO2 interface. Herein, a novel KV2D dye with double squaraine acceptor and double carboxylic acid anchoring groups is designed to achieve a high extinction coefficient (epsilon, 3.57 x 105M-1cm-1) and robust binding to the TiO2 film for an effective electron transfer. We systematically changed the amount of coadsorbent chenodeoxycholic acid (CDCA) to control the aggregation of dyes on the TiO2 surface that improves the power conversion efficiency (PCE, eta) for the devices based on the doubleanchoring KV2D. Out of these devices, KV2D: CDCA (1:10) based cell exhibited the best PCE of 5.26\% with VOC of 754 mV, JSC of 10.41 mA/cm2, and ff of 67\%. The sequential cosensitization studies were carried out with a far-red active dye to find the effect of the strong binding of the sensitizer to the TiO2 film. Interestingly, when di-anchoring, KV2D was sensitized first for 12 h and then sequentially cosensitized with far-red absorbing SQS4 for 5 h to achieve a PCE of 5.0\% with VOC of 697 mV, JSC of 10.23 mA/cm2, and ff of 70\% with panchromatic spectral response in IPCE upto 730 nm giving higher photocurrent generation.

}, keywords = {aggregation of dyes, Bulky donor unit, Double acceptor dye, Dye-sensitized solar cells, self-assembly of dye, squaraine dyes, triazatruxene}, issn = {1010-6030}, doi = {10.1016/j.jphotochem.2024.116229}, author = {Ingole, Kiran Balaso and Siby, Jesna and Pandya, Rinu and Vanka, Kumar and Krishnamoorthy, Kothandam and Nithyanandhan, Jayaraj} }