Squaraine dyes are promising chromophores to harvest visible and near-infrared (NIR) photons. A series of indoline-based unsymmetrical squaraine (SQ) dyes that contain alkyl chains at sp C- and N- atoms of indoline moieties with a carboxylic acid anchoring group were synthesized. The optical and electrochemical properties of the SQ dyes in solution were nearly identical as there was no change in the D-A-D SQ framework; however, remarkable changes with respect to the power conversion efficiencies (PCE) were observed depending upon the position of alkyl groups in the dye. Introduction of alkyl groups to the indoline unit that was away from anchoring unit were helped in more dye loading with controlled organization of dyes on surface, increased charge transfer resistance, long electron lifetime, and hence higher PCE than that of the corresponding isomer in which the alkyl groups funtionalized indoline unit contains the carboxylic acid anchoring group. Careful analysis of incident photon-to-current conversion efficiency (IPCE) profiles indicated the presence of aggregated structure on the TiO surface that contributes to the charge injection in the presence of a coadsorbent. A dye-sensitized solar cell (DSSC) device made out of SQ5 was achieved an efficiency of 9.0%, with an open-circuit potential (V) of 660 mV and short-circuit current density (J) of 19.82 mA/cm, under simulated AM 1.5G illumination (100 mW/cm). The IPCE profile of SQ5 shows an onset near to 750 nm with a good quantum efficiency (>80%) in the range of 550-700 nm, indicating the importance of self-organization of dyes on the TiO surface for an efficient charge injection. This present investigation revealed the importance of position of alkyl groups in the squaraine-based dyes for the better PCE.
Organic dyes possessing conjugated π-framework forms closely packed monolayers on photoanode in dye-sensitized solar cell (DSSC), because of the limitation to control the orientation and the extend of intermolecular π-π interaction, self-aggregation of dyes leads to reduced cell performance. In this report, a series of homodimeric (D-D and D-D) and heterodimeric (D-D and D-D) donor/acceptor (D/A) dyes containing spiroBiProDOT π-spacer were designed and synthesized by utilizing Pd-catalyzed direct arylation reaction and correlates the device performance with monomeric dyes (D and D). Both the thiophenes (π-spacer) of spiroBiProDOT were functionalized with same or different donor groups which led to homodimeric and heterodimeric chromophores in a single sensitizer. The homodimeric spiro-dye D-D showed higher power conversion efficiency (PCE), of 7.6% with a V and J of 0.672 V and 16.16 mA/cm, respectively. On the other hand, the monomeric D exhibited a PCE of 3.2% (V of 0.64 V and J of 7.2 mA/cm), which is lower by 2.4 fold compared to dimeric analogue. The spiro-unit provides flexibility between the incorporated chromophores to orient on TiO due to four sp-centers, which arrest the molecular motions after chemisorption. This study shows a new molecular approach to incorporate two chromophores in the dimeric dye possessing complementary absorption characteristics toward panchromatic absorption. The attenuated charge recombination at TiO/Dye/redox couple interface in case of D-D, owing to better passivation of TiO surface, was elucidated through impedance analysis. The FT-IR spectrum of D-D adsorbed on TiO film indicated both the carboxylic units were involved in chemisorption which makes strong coupling between dye and TiO.
Silicon (Si) on-chip metallization was carried out through surface functionalization and electroless deposition of copper (Cu). Surface functionalization of Si was performed by grafting an amine (NH 2 )-terminated organosilane, 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (ETAS), as a nanoscaled bridge linker to adsorb catalytic polyvinylpyrrolidone-capped palladium nanoclusters (PVP-nPd) through complex reaction. The ETAS molecules bear three methoxy groups that can transform into the hydroxyl groups through hydrolysis and attach to the SiO 2 /Si substrate by hydrogen bonding. Through rapid thermal annealing (RTA) treatment, the dehydration reaction occurred and led to the formation of the covalent bonding of siloxane (Si−O−Si) between ETAS and SiO 2 /Si. The increase of the RTA temperature to 673 and 773 K caused the increase of the Si−O−Si bonding which improved the grafting orientation of ETAS as suggested by the molecular simulation. The adhesion strength of electrolessly deposited Cu film on SiO 2 /Si is boosted to 4 MPa (673 K) and 5.6 MPa (773 K) which is 60−124% enhancement compared to the sample without the RTA treatment (2.5 MPa). This shows its high feasibility induced by the organosilane nanolayer as molecular adhesive for next-generation Si metallization.
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