title: Effect of Out-of-Plane Alkyl Group's Position in Dye-Sensitized Solar Cell Efficiency: A Structure-Property Relationship Utilizing Indoline-Based Unsymmetrical Squaraine Dyes.
abstract: 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 sp3C- 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 TiO2surface 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 (Voc) of 660 mV and short-circuit current density (Jsc) of 19.82 mA/cm2, under simulated AM 1.5G illumination (100 mW/cm2). 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 TiO2surface 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.
authors.affiliation: Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, CSIR-Network of Institutes for Solar Energy , Dr. Homi Bhaba Road, Pune 411008, India.
authors.forename: Ananthan
authors.initials: A
authors.lastname: Alagumalai
authors.affiliation: Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, CSIR-Network of Institutes for Solar Energy , Dr. Homi Bhaba Road, Pune 411008, India.
authors.forename: Munavvar Fairoos
authors.initials: MF
authors.lastname: M K
authors.affiliation: Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, CSIR-Network of Institutes for Solar Energy , Dr. Homi Bhaba Road, Pune 411008, India.|Academy of Scientific and Innovative Research (AcSIR) , New Delhi 110025, India.
authors.forename: Punitharasu
authors.initials: P
authors.lastname: Vellimalai
authors.affiliation: Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, CSIR-Network of Institutes for Solar Energy , Dr. Homi Bhaba Road, Pune 411008, India.|Academy of Scientific and Innovative Research (AcSIR) , New Delhi 110025, India.
authors.forename: Manik Chandra
authors.initials: MC
authors.lastname: Sil
authors.affiliation: Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, CSIR-Network of Institutes for Solar Energy , Dr. Homi Bhaba Road, Pune 411008, India.|Academy of Scientific and Innovative Research (AcSIR) , New Delhi 110025, India.
authors.forename: Jayaraj
authors.identifier: http://orcid.org/0000-0002-3429-4989
authors.initials: J
authors.lastname: Nithyanandhan
keywords: dye aggregation; dye-sensitized solar cells; in-plane and out-of-plane branching units; organic sensitizers; unsymmetrical squaraine dye