@article {46998,
	title = {Alkyl-group-wrapped unsymmetrical squaraine dyes for dye-sensitized solar cells: branched alkyl chains modulate the aggregation of dyes and charge recombination processes},
	journal = {ACS Applied Materials \& Interfaces},
	volume = {12},
	year = {2020},
	month = {JAN},
	pages = {2555-2565},
	type = {Article},
	abstract = {<p>Electron transfer processes at the interfaces dictate the factors that improve the photovoltaic parameters, such as open-circuit voltage (V-oc) and short-circuit current (J(sc)), of a dye-sensitized solar cell device, besides selection of a set of suitable anode, dye, electrolyte, and cathode materials. An inefficient charge injection process at the dye-TiO2 interface and charge recombination at the TiO2-dye/electrolyte interface have detrimental effects on improving both J(sc) and V-oc. Hence, tailoring the factors that govern the improvement of J(sc) and V-oc will be an ideal approach to get the desired sensitizers with good device efficiencies. Squaraines are far-red-active zwitterionic dyes and have a high molar extinction coefficient along with unique aggregation properties due to the large dipole moment associated with them. Here, we report a series of unsymmetrical squaraine dyes, SQS1 to SQS6, with systematic variation of alkyl groups at the sp(3)-C and N-atoms of the indoline unit that is away from the anchoring group to control the dye-dye interactions on the TiO2 surface. The branched alkyl groups help in modulating the self-assembly of sensitizers on the TiO2 surface, besides passivating the surface that helps avoid the charge recombination processes. Light harvesting efficiency and cyclic voltammetry studies of dye-sensitized TiO2 electrodes indicate that the aggregation and charge hopping process between the dye molecules can be modulated, respectively, by systematically increasing the number of carbon atoms in the alkyl groups. Such a variation in the branched alkyl group helps enhance V-oc from 672 (SQS1) to 718 mV (SQS6) and J(sc) from 7.95 (SQS1) to 12.22 mA/cm(2) (SQS6), with the device efficiency ranging from 3.82\% to 6.23\% without any coadsorbent. Dye SQS4 achieves the highest efficiency of 7.1\% (V-oc = 715 mV, J(sc) = 13.05 mA/cm(2)) with coadsorbent chenodeoxycholic acid (CDCA) using an iodine (I-/I-3(-)) electrolyte compared to its analogues. An analysis of the incident photon-to-current efficiency profiles indicates that the major contribution to photocurrent generation is from the aggregated squaraine dyes on TiO2.</p>
},
	keywords = {aggregation of dye, charge injection, charge recombination, Dye-sensitized solar cells, unsymmetrical squaraines},
	issn = {1944-8244},
	doi = {10.1021/acsami.9b19809},
	author = {Singh, Ambarish Kumar and Kavungathodi, Munavvar Fairoos Mele and Nithyanandhan, Jayaraj}
}
@article {47789,
	title = {Amphiphilic indoline-based unsymmetrical squaraine dyes for dye-sensitized solar cells: modulating the dye-TiO2/electrolyte interface for nonaqueous and aqueous electrolytes},
	journal = {ACS Applied Energy Materials},
	volume = {4},
	year = {2021},
	month = {NOV},
	pages = {13932-13942},
	type = {Article},
	abstract = {A high molar extinction coefficient with sharp absorption properties from the range of visible to near-infrared regions makes squaraine dyes very attractive and potential chromophores for dye-sensitized solar cell (DSSC) applications. Here, we report a series of alkyl groups and glycolic chain [triethylene glycol (TEG)]-wrapped amphiphilic indoline-based unsymmetrical squaraine dyes, where the number of carbon atoms in the alkyl groups and TEG was systematically changed by incorporating the alkyl groups and TEG within the dye molecule for controlling the self-assembly of the dyes on the TiO2 surface and to improve the interfacial properties at the dye-TiO2/electrolyte interface. Due to the same skeletal characteristics, ASQ dyes showed similar photophysical and electrochemical properties in solution. Photovoltaic characterization of ASQ dyes was carried out in nonaqueous and aqueous electrolytes to evaluate the effect of alkyl groups and TEG on nonaqueous and aqueous DSSC device performances. VOC, JSC, and photovoltaic efficiencies were systematically enhanced by increasing the number of carbon atoms of alkyl groups into the dye molecules for nonaqueous DSSCs. Furthermore, addition of chenodeoxycholic acid (CDCA) decreased the charge recombination processes and resulted in enhanced efficiency, VOC, and JSC (enhanced incident photon-to-current conversion efficiency performance) compared to that without CDCA. The ASQ4 dye gave the highest nonaqueous DSSC efficiency of 6.39\%, a VOC of 711 mV, and a JSC of 12.18 mA/cm2 with 2 equiv of CDCA in the ASQ dye series. Furthermore, increased carbon atoms in the alkyl groups showed a detrimental effect on the aqueous DSSC efficiency due to the mismatch in the polarity at the dye-TiO2/electrolyte interface, being the reason for the decreased device efficiencies from ASQ2 to ASQ4 dyes. The ASQ2 dye gave the highest aqueous DSSC efficiency of 2.36\%, a VOC of 611 mV, and a JSC of 4.75 mA/cm2 without CDCA in the ASQ dye series.},
	doi = {10.1021/acsaem.1c02733},
	url = {https://doi.org/10.1021/acsaem.1c02733},
	author = {Singh, Ambarish Kumar and Nithyanandhan, Jayaraj}
}
@article {48934,
	title = {Aniline and indoline donors based far-red active unsymmetrical squaraine dyes for dye sensitized solar cells},
	journal = {Chemphotochem},
	volume = {8},
	year = {2024},
	month = {FEB},
	type = {Article},
	abstract = {<p>In dye-sensitized solar cells (DSSC), controlling the dye-aggregation on the metal-oxide surface by appending the alkyl groups around the donor or pi-spacer unit of the dye is a potential approach to enhance DSSC efficiency. Further, rigidification of the dye structures by cyclization modulates the photophysical properties of the sensitizer. Here a series of donor-acceptor-donor (D-A-D) type far-red active unsymmetrical squaraine dyes (SQA) have been designed and synthesized, where N,N-dimethylaniline, methylated- and branched-indoline have been used as donor units. These dyes showed absorption between 629-654 nm (lambda max) with the molar extinction coefficient of 1.49-1.94x105 M-1 cm-1. Systematic enhancements in DSSC device efficiency have been observed due to the cyclization and alkyl-groups incorporation in this set of dyes which were further enhanced with the addition of chenodeoxycholic acid (CDCA). The highest DSSC device efficiency of 4.78 \% (Jsc of 8.77 mA/cm2 and Voc of 692 mV) has been achieved for SQA3. The IPCE profile of SQA dyes indicates the contribution of aggregated structures for the photocurrent generation. Further, co-sensitization of SQA3 dye with a complementary visible light active dye AK4 showed the enhanced device efficiency of 6.27 \% with panchromatic IPCE response. Dye rigidification, and controlled aggregation of dyes on TiO2 by means of cyclization of donor unit and introducing the alkyl groups in the dye structure synergistically improve the dye-sensitized solar cell (DSSC) device performance. Donor-Acceptor-Donor (D-A-D) based unsymmetrical squaraine dye SQA3 showed the DSSC device performance of 4.78 \%.image</p>
},
	keywords = {co-sensitization, dye-sensitized solar cell, effect of alkyl chain, molecular planarity, squaraine dye},
	issn = {2367-0932},
	doi = {10.1002/cptc.202300160},
	author = {Jadhav, Avinash P. and Singh, Ambarish Kumar and Maibam, Ashakiran and Krishnamurty, Sailaja and Krishnamoorthy, Kothandam and Nithyanandhan, Jayaraj}
}
