Molecular engineering of indoline based organic sensitizers for highly efficient dye-sensitized solar cells

Abstract

The increasing electron-donating ability of the donor part is focused to further optimize the lightharvesting capability. Our strategy is to introduce an additional donor group into the indoline unit in the donor part to form a donor-donor structure (D-D moiety). Three different units (carbazole, fluorene and 4-methylphenyl groups) with different degrees of electron-donating capability are incorporated, thus constructing the specific donor-donor-p-acceptor (D-D-p-A) system (C-CA, F-CA and I-3) and giving a systematic view of the absorption evolution. Through molecular engineering, their light-harvesting capabilities, energy levels and photovoltaic performances were studied. As expected, utilizing strong electron-donating carbazole unit as additional donor, the IPCE spectrum of DSSC based on C-CA is successfully broadened to NIR region on the premise of suitable LUMO level, with an extraordinarily high plateau in visible region till around 700 nm. In the system of C-CA and F-CA, the introduction of n-pentyl group in donor part of carbazole and fluorene unit has little effect on preventing the molecular p-aggregation due to the good co-planarity of p-linker (vinyl thiophene), suggesting that the most effective way to prevent p-aggregation is still the incorporation of long alkyl groups into planar p-linker segment. However, the introducing long alkyl group can effectively prevent the electron recombination between electrons in conduction band (CB) of TiO 2 and I 3À ions. Along with the preferable light-harvesting capability, C-CA presents excellent IPCE performance with a short-circuit photocurrent (J sc ) of 18.53 mA cm À2 , an open-circuit photovoltage (V oc ) of 649 mV, a fill factor of 0.71, corresponding to a power conversion efficiency (h) of 8.49%. The internal relations between chemical structure and conversion efficiency provide a strategy for developing highly efficient organic sensitizers working in whole visible region with high photovoltaic performance.

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

“…21 The dye 4d showed comparatively small red-shift, probably, due to the alkyl groups present at C9 of fluorene which may impose hindrence for the close assembly of the dyes when compared to its congener dye 4e which contains carbazole bearing one alkyl chain. 22 All the dyes are weakly emitting in dichloromethane solutions with blue to yellow emission as displayed in Fig. 7.…”

“…1 Probably, the alkyl groups on C9 position of fluorene provides a hydrophobic environment to repel the ionic electrolyte from approaching TiO 2 surface. 8b, 22,39 Fig. 13 shows Nyquist and Bode phase plots of the devices under illumination.…”

Novel synthetized near infrared cyanine dyes as sensitizer for dye sensitized solar cells based on nano-TiO2

“…The best DSSC performance of dye 5 can be attributed to the two methyl group in the indole ring which restricts the intramolecular interactions. The effective way to prevent π-aggregation and charge recombination is still the incorporating of the alkyl chain into the π-bridge (Liu et al, 2012). The novel synthesized cyanine dyes 3-5 shows a low efficiency values, this may be attributed to the intermolecular aggregations of the dyes on TiO2 films.…”

Accelerated Discovery of Potential Organic Dyes for Dye‐Sensitized Solar Cells by Interpretable Machine Learning Models and Virtual Screening

“…[41][42][43] Herein, 44 unique functional units, including 20 D, 12 π, 6 A, and 6 Aa units (see Figure 5), are applied to construct candidate dyes for virtual screening. Among them, most units are derived from synthesized organic dyes with excellent performance, such as indoline derivatives (D1 and D3), [44][45][46] tetrathiophene (π11), [14] and cyanoacrylic acid (A1), [47] whereas some are derived from previous theoretical works, such as nitrogen-doped triphenylamine derivatives (D20) [48] and dithio-cyanoacrylic acid (A2). [49] Different types of building units are randomly connected in D-π-A and D-Aa-π-A configurations, automatically generating a total of 10 080 molecules.…”