The Role of π Bridges in High‐Efficiency DSCs Based on Unsymmetrical Squaraines

Abstract

A series of squaraine-based sensitizers with various π bridges and anchors were prepared and examined in dye-sensitized solar cells. The carboxylic anchor group was attached onto a squaraine dye through π bridges with and without an ethynyl spacer. DFT studies indicate that the LUMO is delocalized throughout the dyes, whilst the HOMO resides on the squaraine core. The dye that incorporates a 4,4-di-n-hexyl-cyclopentadithiophene group that is directly attached onto the π bridge, JD10, exhibits the highest power conversion efficiency in a DSC; this result is attributed, in part, to the deaggregative properties that are associated with the gem-di-n-hexyl substituents, which extend above and below the π-conjugated dye plane. Dye JD10 demonstrates a power-conversion efficiency of 7.3% for liquid-electrolyte dye-sensitized solar cells and 7.9% for cells that are co-sensitized by another metal-free dye, D35, which substantially exceed the performance of any previously tested squaraine sensitizer. A panchromatic incident-photon-to-current-conversion efficiency curve is realized for this dye with an excellent short-circuit current of 18.0 mA cm(-2). This current is higher than that seen for other squaraine dyes, partially owing to a high molar absorptivity of >5,000 M(-1) cm(-1) from 400 nm to the long-wavelength onset of 724 nm for dye JD10.

Strategies for optimizing the performance of carbazole thiophene appended unsymmetrical squaraine dyes for dye-sensitized solar cells

“…13 Recently Grätzel's group reported 7.3% efficiency for a particular class of unsymmetrical squaraines. 14,15 In the present paper, we report the synthesis, characterization and 10 photovoltaic performance of two unsymmetrical squaraine sensitizers. These dyes are characterized by a carbazole thiophene donor unit and an indolium acceptor unit.…”

Indolizine‐Based Donors as Organic Sensitizer Components for Dye‐Sensitized Solar Cells

“…TPAs and indolines are two of the most common DSC donors in organic dye designs that are common to nearly all organic sensitizers with greater than 10% PCE. [ 6,19 ] Indolizine donors exhibit substantially broader solution absorption spectra (narrowed optical band gap) compared with these donors (λ onset = 675 nm for AH6 vs λ onset = 540 nm for TPAbased CQ1 , [ 11 ] 590 nm for diMeO-TPA-based C1 , [ 12 ] and 600 nm for indoline-based LS1 , [ 13 ] Figure 7 ) and increased performance beyond 650 nm in DSC devices (Figure 6 ).…”

Titanium Dioxide Modifications for Energy Conversion: Learnings from Dye-Sensitized Solar Cells

“…Dye solution co-adsorbing additives "Soft modification," simple rinse and dry to alter TiO 2 /dye/electrolyte interface favorably is to add additives along with the dye adsorption solution known as "co-adsorbents" [95][96][97][98]. These additives are also known as de-aggregating agents which aid in favorable dye orientation on TiO 2 and increased electron injection through minimization of dye-dye intermolecular charge transfer and π-π stacking [99]. These mainly insulating additives are known to occupy the vacant spaces among dye molecules which prevents the diffusion of oxidized redox species (e.g., I 3 À ) to TiO 2 ( Figure 7) [100,101].…”