Title: Molecular engineering of fluorescein dyes as complementary absorbers in dye co-sensitized solar cells

Abstract

Fluorescein dye derivatives exhibit extended optical absorption up to 500 nm, rendering these compounds suitable as co-absorbers in dye-sensitized solar cells (DSCs). A molecular engineering approach is presented, which embraces this intrinsic optical attribute of fluoresceins, while modifying the dye chemistry to enhance their light harvesting efficiency, in order to effectively tailor them for DSC applications. This approach first realizes relationships between the molecular structure and the optoelectronic properties for a series of five a priori known (parent) fluorescein dyes: 5-carboxyfluorescein (1), a mixture of m-carboxyfluorescein where m = 5 or 6 (2), 5-carboxyfluorescein diacetate (3), 6-carboxyfluorescein diacetate (4), a mixture of n-carboxy-2',7'-dichlorofluorescein diacetate where n = 5 or 6 (5). The first step in this approach combines, where available, experimental and computational methods so that electronic structure calculations can also be validated for representative fluorescein dyes. Such calculations can then be used reliably to predict the structure and properties of fluorescein dyes for cases where experimental data are lacking. Structure-function relationships established from this initial step inform the selection of parent dye 1 that is taken forward to the second step in molecular engineering: in silico chemical derivation to re-functionalize 1 for DSC applications. For this purpose, computational calculationsmore » are used to extend the charge conjugation in 1 between its donor and acceptor moieties. These structural modifications result in a bathochromic shift of the lowest excitation by ~1.3-1.9 eV (100-170 nm), making the dye optically absorb in the visible region. Further calculations on dye molecules adsorbed onto the surface of a TiO₂ cluster are used to investigate the dye sensitization behavior via dye adsorption energies and anchoring modes. The results of this theoretical investigation lead to two molecularly engineered fluoresceins being proposed to act as co-sensitizers together with a rhodamine dye. This combination of three dyes ensures chemical compatibility, panchromatic absorption, and restores optical absorption dipping otherwise observed in a DSC device at ~350-400 nm owing to the I-/I-₃ electrolyte. Altogether, the results of this study demonstrate that molecular engineering can be used to identify suitable chemical modifications for organic dyes with improved light harvesting properties for photovoltaic applications.« less

Authors:

Pepe, Giulio ^[1]; Cole, Jacqueline M. ^[2]; Waddell, Paul G. ^[3]; Griffiths, Joseph R. D. ^[1]

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+ Show Author Affiliations

1. Univ. of Cambridge, Cambridge (United Kingdom)
2. Univ. of Cambridge, Cambridge (United Kingdom); STFC Rutherford Appleton Lab., Didcot (United Kingdom); Argonne National Lab. (ANL), Argonne, IL (United States)
3. Univ. of Cambridge, Cambridge (United Kingdom); Australian Nuclear Science and Technology Organization, Lucas Heights (Australia)

Publication Date:

Thu Sep 22 00:00:00 EDT 2016

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1353035

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Molecular Systems Design & Engineering

Additional Journal Information:

Journal Volume: 1; Journal Issue: 4; Journal ID: ISSN 2058-9689

Publisher:

Royal Society of Chemistry

Country of Publication:

United States

Language:

English

Subject:

14 SOLAR ENERGY