Simple Metal-Free Organic D-π-A Dyes with Alkoxy- or Fluorine Substitutions: Application in Dye Sensitized Solar Cells

Abstract

Two new metal-free organic sensitizers with simplest structural variations have been synthesized for application in nanocrystalline TiO2 sensitized solar cells. The donor-pi-bridge-acceptor (D-pi-A) structure dyes, Y2 and Y3 each designed with three parts, an electron donor unit (substituted phenyl), a linker unit (thiophene), and an anchor unit (cyanoacrylic acid) showed maximal monochromatic incident photon to current conversion efficiencies (IPCE) in a device reaching upto 67% and 82% respectively. The organic sensitizers with 3,4,5-trimethoxy phenyl (Y3) as donor moieties obtained better solar light to electrical energy conversion efficiencies of 3.30% where as the organic sensitizer with 2,4-difluoro phenyl as donor (Y2) showed comparatively lower efficiency of 1.02%. The efficiency obtained with the reference sensitizer N719 under similar fabrication and evaluation conditions was 5.84%.

Thermal Fluctuations on Förster Resonance Energy Transfer in Dyadic Solar Cell Sensitizers: A Combined Ab Initio Molecular Dynamics and TDDFT Investigation

“…Up to the “perovskite” revolution in 2012, , dye-sensitized solar cells (DSSCs) − have represented the leading alternative technology to traditional silicon-based devices, with top certified efficiency exceeding 11% and laboratory-cell efficiency above 13% . Although the highest-performance devices employing liquid I – /I 3 – electrolyte are sensitized with Ru­(II)-based dyes, − a variety of metal-free dyes were developed, − with overall efficiencies reaching 13% when a cobalt-based electrolyte is employed. ,− Panchromatic sensitization of the electron transporting semiconductor, generally TiO 2 , is achieved in this case either by optimizing the optical and structural properties of individual dyes or by mixing different sensitizers (“co-sensitization”) having complementary absorption spectra. − Co-sensitization presents however two main drawbacks: (i) restrictions due to a limited TiO 2 loading and (ii) difficulties in controlling and optimizing the coadsorption geometry to increase the light collection efficiency and suppress parasitic deactivation pathways. Alternatively, a widely employed molecular engineering approach to increase the dye efficiency by extending the portion of absorbed light consists in loading dyes with tethered “antenna” systems, − the latter having the role of collecting photons and redirecting the captured energy via long-range energy transfer (so-called Förster or fluorescence-detected resonance energy transfer, hereafter FRET) to the sensitizing dye, which is adsorbed onto the semiconductor surface …”

A New Series of EDOT Based Co-Sensitizers for Enhanced Efficiency of Cocktail DSSC: A Comparative Study of Two Different Anchoring Groups

“…The observed enhanced V oc of cocktail DSSC devices could be attributed to the decreased recombination rate between the injected electrons in the conduction band of TiO 2 semiconductor and I 3 - species in the redox electrolyte. Owing to their small size, the co-sensitizers provide better surface coverage [19,34,37] by getting adsorbed into the pores and gaps on TiO 2 , whereas the ruthenium-based dye molecules cannot get absorbed (discussed in detail in dye loading section). Though RA based co-sensitizers have shown high absorption properties in DMF solvent than CA based dyes, it could not be transformed into high efficiency.…”

“…It was mostly because of a change in the molecular size of the dyes, which was able to adequately adsorb on the surface of the TiO 2 semiconductor, thereby enabling the device to harvest a larger number of incident photons from the light [35,36]. Inspired by these results various research groups, [35], in addition to our group [33,35,36,37,38], designed numerous organic co-sensitizers using high electron donors such as triphenylamine, indole, carbazole, phenothiazine, thiophene, etc. [39].…”

An Integrated Experimental and Theoretical Approach to the Spectroscopy of Organic‐Dye‐Sensitized TiO2 Heterointerfaces: Disentangling the Effects of Aggregation, Solvation, and Surface Protonation

“…The sensitizer plays a key role in the operation of the devices because it is responsible for the absorption of solar radiation and the subsequent charge-separation process. Recently, a number of promising metal-free organic dyes have been developed [5,6] with overall efficiencies that approach 10 %. [7,8] Organic dyes exhibit many advantages compared with metal-organic dyes, such as the ease of molecular structure design and synthesis, high molar extinction coefficients, the possibility of extending absorption spectra in the visible range as a result of the incorporation of different light-absorbing groups, and reduced production costs.…”