Importance of fluorescence lifetimes for efficient indoline dyes in dye-sensitized solar cells

Abstract

To make a molecular design of efficient indoline dyes, fluorescence lifetimes should be longer than ca. 0.8 ns in chloroform, in addition to suitable HOMO and LUMO levels and bathochromic UV-vis absorption bands.Indoline dyes are one of the most efficient organic sensitizers in dye-sensitized solar cells (DSSCs). D149 was reported to exhibit a high conversion efficiency of 6.1% on titanium oxide. 1 Since then, much effort has been made to obtain more efficient indoline dyes by changing the anchor moieties such as cyanoacrylic acid, 2,3 single, 4,5 double, 6-9 and triple rhodanines. 10 The double rhodanine dyes D205, 6 DN319, 7 and DN315, 8 have been reported to exhibit higher efficiency than D149. As the acceptor anchor moieties affect the energy levels of indoline dyes, it is important to check the HOMO and LUMO levels. The relationship between the HOMO level and maximum incident photon-to-current efficiency (IPCE) of indoline dyes has been reported. 11 As the HOMO level of double rhodanine indoline dyes is close to the I À /I 3 À redox level, the stabilization of the HOMO level and positive shi of the oxidation potential (E ox ), is required. To prepare new indoline dyes, we made molecular designs of pyridone acetic acid derivatives. These novel indoline dyes, GU113 and GU114, were predicted by the DFT calculations to show stabilized HOMO levels, and similar HOMO-LUMO gaps to D149. Unfortunately, these dyes did not act as sensitizers due to reduced electron injection abilities from the excited state to the conduction band of zinc oxide. To obtain efficient indoline dyes, an additional parameter of electron injection, besides the DFT calculations, is proposed in this report. Novel indoline dyes GU113 and GU114 were synthesized as shown in Scheme 1. Ethyl alkanoylacetoacetates 1, ethyl cyanoacetate (2), and glycine ethyl ester hydrochloride (3) were allowed to react in the presence of piperidine to give ethyl pyridone acetates 4, whose ester group was hydrolyzed to afford pyridone acetic acids 5. These compounds were allowed to react with aldehyde 6 to provide GU113 and GU114. D149 was also prepared as a reference compound.The structure of GU113 was optimized at the B3LYP/3-21G level. Fig. 1 indicates that the double bond of GU113 at the 7-position is in the Z conguration due to steric repulsion between the hydrogen atom at the 8-position on the indoline ring, and the methyl group on the pyridone ring. The indoline chromophore is almost planar, with the dihedral angle between the indoline and pyridone moiety q 1 being 0.5 . Meanwhile, the uorenyl moiety can act as steric hindrance to prevent Scheme 1 Reagents and conditions: (i) 3 (20.0 mmol), TEA (29.7 mmol), 5 min, EtOH (2 mL), then 1 (20.0 mmol), 2 (20.0 mmol), piperidine (6.1 mmol), reflux, 9 h, (ii) 4 (1.8 mmol), AcOH-HCl (2 : 1, 3 mL), reflux, 3 h, (iii) 5 (0.70 mmol), 6 (0.86 mmol), EtOH (10 mL), rt, 1 day.

Long-term stability of novel double rhodanine indoline dyes having one and two anchor carboxyl group(s) in dye-sensitized solar cells

“…That of DN351 has been reported to be 1.51 ns in chloroform. 33 In our previous work, it was claried that the s f of efficient indoline dyes should be longer than 0.9 ns in chloroform. 33 Thus, these dyes have sufficiently long excitation lifetime to inject electrons from the excited singlet state to titanium oxide.…”

Graphene based photoanode for DSSCs with high performances

“…The concentration of dye in the solution is proportional to the integral area of the adsorption peak measured by the UV-visible spectrometer (the adsorption signal was located at $510 nm). 43,44…”

Electronic Structure and Optical Properties of Designed Photo-Efficient Indoline-Based Dye-Sensitizers with D–A−π–A Framework

“…IND dyes have been examined as highly efficient sensitizers for DSSCs because of their intense and stable absorption spectra in the visible zone. This makes them one of the potential top-quality chemical classes for future DSSCs with better PCE. ,,− In our previous study, we have designed IND dyes explicit to iodine electrolyte based on the developed quantitative structure–property relationship (QSPR) model. Subsequently, we screened all designed dyes based on the essential photophysical parameters with the use of quantum chemical calculations.…”