@article { ISI:000323241100045, title = {Enhanced hole carrier transport due to increased intermolecular contacts in small molecule based field effect transistors}, journal = {ACS Applied Materials \& Interfaces}, volume = {5}, number = {15}, year = {2013}, month = {AUG}, pages = {7086-7093}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Small molecules and oligomers can be synthesized with very high purity and precise molecular weights, but they often do not form uniform thin films while processed from solution. Decreased intermolecular contacts between the small molecules are another disadvantage. To increase the intermolecular contacts in small molecules, we have chosen i-indigo, as one of the conjugated molecular units. The electron poor i-indigo has been connected with electron rich triphenylamine to synthesize a donor-acceptor-donor type small molecule. The propeller shaped triphenylamine helps to increase the solubility of the small molecule as well as isotropic charge transport. The intermolecular spacing between the molecules has been found to be low and did not vary as a function of thermal annealing. This implies that the intermolecular contacts between the small molecules are enhanced, and they do not vary as a function of thermal annealing. Organic field effect transistors (OFET) fabricated using a small molecule exhibited a hole carrier mobility (mu) of 0.3 cm(2)/(V s) before thermal annealing. A marginal increase in mu was observed upon thermal annealing at 150 degrees C, which has been attributed to changes in thin film morphology. The morphology of the thin films plays an important role in charge transport in addition to the intermolecular spacing that can be modulated with a judicious choice of the conjugated molecular unit.

}, keywords = {hole mobility, i-indigo, organic field effect transistor, quadrupole interaction, small molecules, triphenylamine}, issn = {1944-8244}, doi = {10.1021/am401379a}, author = {Dharmapurikar, Satej S. and Arulkashmir, Arulraj and Das, Chayanika and Muddellu, Pooja and Krishnamoorthy, Kothandam} } @article {45405, title = {Experimental and theoretical investigations of different diketopyrrolopyrrole-based polymers}, journal = {ACS Omega}, volume = {3}, year = {2018}, month = {SEP}, pages = {11710-11717}, type = {Article}, abstract = {Diketopyrrolopyrrole (DPP)-based polymers are often considered las the most promising donor moiety in traditional bulk heterojunction solar cell devices. In this paper, we report the synthesis, characterization of various DPP-based copolymers with different molecular weights, l and polydisper sity where other aromatic repeating units (phenyl or thiophene based) are connected by alternate double bonds or triple bonds. Some of the copolymers were used for device fabrication and the crucial parameters such as fill factor (FF) and open circuit voltage (V-oc) were calculated. The density functional theory was used to optimize the geometries and deduce highest occupied molecular orbital lowest unoccupied molecular orbital gaps of all the polymers and{\textquoteright}theoretically predict their optical and electronic properties. Optical properties of all the polymers, electrochemical properties and band gaps were also obtained experimentally and compared with the theoretically predicted values.}, doi = {10.1021/acsomega.8b01132}, author = {Murugan, Pachaiyappan and Raghavendra, Venkatraman. and Chithiravel, Sundaresan and Krishnamoorthy, Kothandam and Mandal, Asit Baran and Subramanian, Venkatesan and Samanta, Debasis} } @article {47154, title = {Enhancing the device efficiency by filling the traps in photoanodes}, journal = {Journal of Materials Chemistry C}, volume = {7}, year = {2019}, month = {DEC }, pages = {14632-14638}, type = {Article}, abstract = {

Traps are ubiquitous in semiconductors and act as recombination sites. These recombination sites have a deleterious effect on the device efficiency. Thus, trap filling is used to increase the efficiency of devices. The traps are filled by dopants that either inject or extract electrons to/from the semiconductor. The trap-filled devices exhibit superior performance as compared to their unfilled counterparts. However, to date, this approach has not been explored in dye-sensitized solar cells despite the well-established presence of traps in them. The traps in the TiO2 photoanode are due to the presence of oxygen vacancies. Therefore, herein, we treated the photo anodes with hydrazine and filled the traps that increased all device metrics. Moreover, further sintering of the trap-filled photoanodes in the presence of hydrazine led to the formation of a nitrogen-doped photoanode. The device comprising a nitrogen-doped photoanode exhibited the efficiency increase of 23\%. The detailed analysis of the device performance led to the conclusion that trap filling suppressed back electron transfer and increased the photo conversion efficiency.

}, issn = {2050-7526}, doi = {10.1039/c9tc04740a}, author = {Sudhakar, Vediappan and Krishnamoorthy, Kothandam} } @article {45478, title = {Evolution of ZnO nanostructures as hexagonal disk: Implementation as photoanode material and efficiency enhancement in Al: ZnO based dye sensitized solar cells}, journal = {Applied Surface Science}, volume = {470}, year = {2019}, month = {MAR}, pages = {1130-1138}, type = {Article}, abstract = {

Hexagon shaped pristine and Al doped ZnO nanodisks (NDs) with exposed +/- [0001] polar facets were successfully synthesized using modified sol-gel method without the involvement of any structural directing or capping agents. It was investigated that OH- ions in mixed solvent system is responsible for pore formation and inhibit the growth of ZnO along the direction of c-axis leading to a high percentage exposure of active +/- [0001] polar facets and encourage the formation of ZnO NDs. Crystallographic analysis revealed that crystallite size and lattice constants are decreased, with the addition of Al3+ ions. The results obtained from Raman, and XPS analysis further corroborated with the XRD results, revealed the successful incorporation of Al3+ ions into ZnO lattice. Optical study revealed the band gap tunability with the incorporation of Al ion as dopant. Enhanced power conversion efficiency (PCE) of 1.96\% (J(sc) similar to 7.69 +/- 0.23 mA/cm(2)) was observed for Al: ZnO hexagonal NDs based DSSC. The increased PCE in Al: ZnO based DSSC can be attributed to the higher inner surface area for dye anchoring by the interconnected network of the disk-like structure. The obtained results were satisfactory and most importantly the synthesis procedure proposed in present work is excellent for the synthesis of perfectly hexagonal shaped disks under precised synthesis parameters. The device interface study was further conducted using electrochemical impedance spectroscopy which revealed better charge transport process and charge storage ability with the incorporation of Al3+ ions into ZnO lattice.

}, keywords = {dye sensitized solar cells, Hexagonal disks, Sol-gel method, ZnO}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2018.11.077}, author = {Parra, Mohammad Ramzan and Pandey, Padmini and Siddiqui, Hafsa and Sudhakar, Vediappan and Krishnamoorthy, Kothandam and Haque, Fozia Z.} } @article {46937, title = {Effect of aromatic rings and substituent on the performance of lithium batteries with rylene imide cathodes}, journal = {ChemElectroChem}, volume = {7}, year = {2020}, month = {MAR }, pages = {1160-1165}, type = {Article}, abstract = {

Rylene imides (RIs) are attractive organic battery materials because of the inherent modularity of the molecules. While strong aggregation of RIs is disadvantageous for fast lithium-ion transport in the organic active material, decreasing the solubility of the RIs in battery electrolytes is essential to avoid performance fading. Therefore, the design and synthesis of RIs for lithium batteries is a non-trivial task that must, among other considerations, balance lithium-ion transport in the solid material vs. low solubility by controlling aggregation and packing. We have chosen triphenylamine (TPA) as a substituent which disrupts the aggregation but maintains a low solubility due to increased aromaticity of TPA. We have synthesized three RIs with one, two, and four aromatic units in the core. All of them showed stable specific capacity over 300 charge-discharge cycles. The batteries also showed specific capacities close to their theoretical capacities with 97-99 \% coulombic efficiency. The maximum specific energy and specific power were 197 mWh g(-1) and 37 mW g(-1), respectively.

}, keywords = {lithium-ion batteries, organic cathode material, rylene imides, solubility, triphenylamine}, issn = {2196-0216}, doi = {10.1002/celc.202000118}, author = {Aher, Jagdish and Graefenstein, Alexander and Deshmukh, Gunvant and Subramani, Kumar and Krueger, Bastian and Haensch, Mareike and Schwenzel, Julian and Krishnamoorthy, Kothandam and Wittstock, Gunther} } @article {48949, title = {Electrocatalytic hydrogen evolution mediated by an organotelluroxane macrocycle stabilized through secondary interactions}, journal = {Dalton Transaction }, volume = {52}, year = {2023}, month = {NOV }, pages = {17242-17248}, type = {Journal Article}, abstract = {

A discrete liphophilic organotelluroxane macrocycle has been found to catalyse the hydrogen evolution reaction (HER) by proton reduction efficiently. The macrocycle is synthesized via chloride abstraction from bis(p-methoxyphenyl) tellurium dichloride (p-MeOC6H5)2TeCl2 (1) by silver salts AgMX4 (MX4 = BF4-, and ClO4-) resulting in in situ generated di-cationic tetraorganoditelluroxane units; two such units are held together by two weak anions mu 2-MX4, bridging to form 12-membered di-cationic macrocycles [((p-MeO-C6H4)2Te)2(mu-O)(mu 2-F2BF2)2]2+ (2) and [((p-MeO-C6H4)2Te)2(mu-O)(mu 2-O2ClO2)2]2+ (3) stabilized via Te-(mu 2-BF4/ClO4), with secondary interactions. The charge is balanced by the presence of two more anions, one above and another below the plane of the macrocycle. Similar reaction at higher temperatures leads to the formation of telluronium salts R3TeX [X = BF4- (4), ClO4- (5)] as a major product. The BF4- anion containing macrocycle and telluronium salt were monitored using 19F NMR. HRMS confirmed the structural stability of all the compounds in the solution state. The organotelluroxane macrocycle 2 has been found to act as an efficient electrocatalyst for proton reduction in an organic medium in the presence of p-toluene sulfonic acid as a protic source. A discrete liphophilic organotelluroxane macrocycle has been found to catalyse hydrogen evolution reaction (HER) by proton reduction efficiently.

}, keywords = {Anion Transport, Proton-Reduction}, issn = {1477-9226}, doi = {10.1039/d3dt02746e}, author = {Narsimhulu, Gujju and Samuel, Calvin and Palani, Sathishkumar and Dasari, Sai Hemant Kumar and Krishnamoorthy, Kothandam and Baskar, Viswanathan} } @article {49037, title = {Effect of position of donor units and alkyl groups on dye-sensitized solar cell device performance: indoline-aniline donor-based visible light active unsymmetrical squaraine dyes}, journal = {ACS Om.}, volume = {9}, year = {2024}, month = {MAR}, pages = {16429-16442}, type = {Article}, abstract = {

Indoline (In) and aniline (An) donor-based visible light active unsymmetrical squaraine (SQ) dyes were synthesized for dye-sensitized solar cells (DSSCs), where the position of An and In units was changed with respect to the anchoring group (carboxylic acid) to have In-SQ-An-CO2H and An-SQ-In-CO2H sensitizers, AS1-AS5. Linear or branched alkyl groups were functionalized with the N atom of either In or An units to control the aggregation of the dyes on TiO2. AS1-AS5 exhibit an isomeric pi-framework where the squaric acid unit is placed in the middle, where AS2 and AS5 dyes possess the anchoring group connected with the An donor, and AS1, AS3, and AS4 dyes having the anchoring group connected with the In donor. Hence, the conjugation between the middle squaric acid acceptor unit and the anchoring -CO2H group is short for AS2, AS5, and AK2 and longer for AS1, AS3, and AS4 dyes. AS dyes showed absorption between 501 and 535 nm with extinction coefficients of 1.46-1.61 x 10(5) M-1 cm(-1). Further, the isomeric pi-framework of An-SQ-In-CO2H and In-SQ-An-CO2H exhibited by means of changing the position of In and An units a bathochromic shift in the absorption properties of AS2 and AS5 compared to the AS1, AS3, and AS4 dyes. The DSSC device fabricated with the dyes contains short acceptor-anchoring group distance (AS2 and AS5) showed high photovoltaic performances compared to the dyes having longer distance (AS1, AS3, and AS4) with the iodolyte (I-/I-3(-)) electrolyte. DSSC device efficiencies of 5.49, 6.34, 6.16, and 5.57\% have been achieved for AS1, AS2, AS3, and AS4 dyes, respectively; without chenodeoxycholic acid (CDCA), small changes have been observed in the device performance of the AS dyes with CDCA. Significant changes have been noted in the DSSC parameters (open-circuit voltage V-OC, short-circuit current J(SC), fill factor ff, and efficiency eta) for the AS5 dye while sensitized with CDCA and showed highest DSSC efficiency of 8.01\% in the AS dye series. This study revealed the potential of shorter SQ acceptor-anchoring group distance over the longer one and the importance of alkyl groups on the overall DSSC device performance for the unsymmetrical squaraine dyes.

}, issn = {2470-1343}, doi = {10.1021/acsomega.4c00123}, author = {Singh, Amrita and Singh, Ambarish Kumar and Dixit, Ruchi and Vanka, Kumar and Krishnamoorthy, Kothandam and Nithyanandhan, Jayaraj} } @article {49516, title = {Effect of cyclization and alkyl group wrapping in visible-light-active unsymmetrical squaraine dyes for dye-sensitized solar cells}, journal = {ACS Applied Energy Materials}, volume = {8}, year = {2025}, month = {APR }, pages = {5017-5030}, type = {Article}, abstract = {

A series of alkyl group-appended indoline- and carboxylic acid-functionalized indolenine-based visible-light-active unsymmetrical squaraine dyes, SQA7-10, were designed, synthesized, and utilized for the dye-sensitized solar cells device fabrication. The number of alkyl group has been increased systematically on the indoline moiety to control the self-assembly of dyes on TiO2 and to passivate the photoanode that helps in improving the open-circuit voltage (V-OC) by avoiding the charge recombination process. SQA7-10 dyes showed an absorption between lambda(max) 536-540 nm, with molar extinction coefficients of 1.62-2.13 x 10(5) M-1 cm(-1) in CH3CN. Further, ultraviolet-visible (UV-vis) studies on TiO2 indicated the formation of H-aggregated dyes (505-510 nm), which can be controlled by appending the alkyl groups. The energy levels of the highest occupied molecular orbital (HOMO) of these dyes are well aligned with the Nernst potentials of I-/I(3)(-)electrolyte and [Cu(tmby)(2)](+/2+) electrolytes with sufficient overpotentials required for the dye regeneration process. DSSC devices made with these dyes showed systematic enhancements of open-circuit voltage (V-OC) and device efficiency with respect to alkyl group incorporation for SQA7-10 with I-/I-3(-) electrolytes. All of the SQA dyes exhibited the device V-OC of more than 805 mV, where the introduction of alkyl groups systematically enhanced the V-OC in the order of SQA7 (805 mV) \< SQA8 (829 mV) \< SQA9 (843 mV) \< SQA10 (862 mV) without any addition of CDCA. Within the SQA dye series, SQA10 dye has achieved the highest DSSC device efficiency of 7.52\% (J(sc) of 11.16 mA/cm(2), V-oc of 862 mV, and ff of 78\%) with I-/I-3(-) electrolyte, whereas use of [Cu(tmby)(2)](+/2+) redox shuttle with SQA10 showed enhanced V-oc (1080 mV) and device efficiency (8.35\%). The IPCE profile for the device fabricated with SQA dyes showed good response at 480 and 560 nm, which indicates the photocurrent generation from the aggregated structures.

}, keywords = {aggregation of dyes, charge recombination, Dye-sensitized solar cells, indoline and indolenine donors, visible-light-activeunsymmetrical squaraine dye}, issn = {2574-0962}, doi = {10.1021/acsaem.4c03116}, author = {Jadhav, Avinash P. and Singh, Ambarish Kumar and Shivankar, Bhavana R. and Siby, Jesna and Krishnamurty, Sailaja and Krishnamoorthy, Kothandam and Nithyanandhan, Jayaraj} }