Functional tuning of organic dyes containing 2,7-carbazole and other electron-rich segments in the conjugation pathway

Abstract

Organic dyes containing triarylamine donor, cyanoacrylic acid acceptor and conjugation pathway composed of 2,7-carbazole, thiophene and fluorene have been synthesized and characterized as sensitizers for TiO2-based dye-sensitized solar cells. The effect of the nature of the conjugation bridge on the optical, electrochemical and photovoltaic properties has been investigated. Elongation of conjugation by the insertion of 2,7-carbazole or 2,7-fluorene π-linkers led to increase in the molar extinction coefficients while the use of terthiophene red-shifted the absorption. Also the lengthening of the π-bridge helped to raise the lowest unoccupied molecular orbital of the dyes relative to the conduction band of TiO2. This increased the thermodynamic driving force for the electron injection from the excited dyes into the conduction band of TiO2. The trends in the optical properties of the dyes were also substantiated by the TDDFT computations. DSSC based on a dye containing terthiophene in the conjugation bridge exhibited the highest power conversion efficiency (4.9%) in the series attributable to its larger photocurrent (JSC = 13.08 mA cm -2 ) generation. However, the dye with fluorene linker exhibited high open circuit voltage (VOC = 632 mV) and prolonged electron lifetime for the device. The role of the π-bridge on the charge transfer and electron recombination kinetics in the DSSC was elucidated by electrochemical impedance spectroscopic studies.

A new sensitizer containing dihexyloxy-substituted triphenylamine as donor and a binary conjugated spacer for dye-sensitized solar cells

“…Indoline 9 , triphenylamine 10,11 , coumarin 12,13 , carbazole 14,15 etc, were widely used as donor moieties in the design of sensitizers, while cyanoacrylic acid was by far the most commonly used anchoring and electron acceptor unit. The structure of π-conjugated bridge can be easily tuned and can comprise a variety of functional units such as phenylenevinylene, benzothiadiazole, thiophene, dithienothiophene, EDOT, selenophene etc 6,16 .…”

Star-Shaped Asymmetrically Substituted Blue Emitting Carbazoles: Synthesis, Photophyscial, Electrochemical and Theoretical Investigations

“…Subsequently, the bromide 3 was reacted with aryl boronic acids in the presence of Pd‐catalyst following Suzuki coupling reaction conditions to obtain 9‐butyl‐9 H ‐carbazole‐3,6‐dicarbaldehyde containing different auxiliary chromophores on C1 & C8 ( 4 a‐d ) . Finally, the precursor aldehydes ( 1 and 4 a‐d ) were treated with N 1 ‐phenyl benzene‐1,2‐diamine in the presence of sodium metabisulfite to obtain target dyes ( 2 and 5 a‐d ) in good yields . The dyes were thoroughly characterized using 1 H, 13 C NMR and HRMS measurements.…”

“…250–380 nm. The higher energy absorption peaks appearing below 320 nm corresponds to the localized π‐π* electronic transitions of N ‐phenylbenzimidazole unit, and the auxiliary chromophores present on C1 & C8 or central carbazole nucleus . The lower energy absorption bands with reasonable intensities centered at ca.…”

Synthesis and photovoltaic properties of organic dyes containing N-fluoren-2-yl dithieno[3,2-b:2′,3′-d]pyrrole and different donors

“…We have recently developed several organic dyes featuring fluorene [48][49][50][51][52][53] or heterocyclic donors [54][55][56][57][58][59][60]. In continuation of our work, we felt that incorporation of fluorene on DTP may result in new chromophore with better electron richness.…”