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Dye nanoaggregate structures in MK-2, N3, and N749 dye…TiO2 interfaces that represent dye-sensitized solar cell working electrodes

DOI: 10.1021/acsaem.9b02002 DOI Help

Authors: Ke Deng (University of Cambridge) , Jacqueline M. Cole (University of Cambridge; Research Complex at Harwell; ISIS Neutron and Muon Source; Argonne National Laboratory) , Jonathan L. Rawle (Diamond Light Source) , Christopher Nicklin (Diamond Light Source) , Hao Chen (University of Cambridge; Research Complex at Harwell) , Angel Yanguas-gil (Argonne National Laboratory) , Jeffrey W. Elam (Argonne National Laboratory) , Gavin B. G. Stenning (ISIS Neutron and Muon Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Applied Energy Materials

State: Published (Approved)
Published: December 2019
Diamond Proposal Number(s): 15487

Abstract: The working electrode of a dye-sensitized solar cell (DSSC) consists of dye molecules adsorbed onto nanoparticles of a semiconductor such as TiO2. A reliable prediction of the DSSC photovoltaic performance of a given dye requires in-depth knowledge about the precise structure of the dye···TiO2 interface. X-ray reflectometry (XRR) and grazing-incidence small angle X-ray scattering (GISAXS) are herein employed to determine the dye···TiO2 interfacial structure and associated dye aggregation behavior of three high-performance DSSC dyes: an organic metal-free dye, MK-2, and the two archetypal ruthenium-based organometallic dyes, N3, and N749 (Black Dye). Results show that all three dyes form nanoaggregates in dye···TiO2 interfaces. We determine the dye nanoaggregate separations, sizes, distribution densities and the extent of short-range order within each dye self-assembly in the longitudinal and lateral directions. Dye···TiO2 composites fabricated using dye solutions of varying concentrations are analyzed. We find that nanoaggregates of the three dyes are separated by several hundred nanometers (158-203 nm) in dye···TiO2 interfaces that have been fabricated using concentrated dye solutions (0.5 mM or 1.0 mM). MK-2 and N749 dyes also display smaller inter-particle separations. Dye nanoparticle diameters are of the order of 156-198 nm, sizes that are comparable to the largest inter-particle separations. Thus, no extraneous dye particles can be fitted into gaps between particles, so the dye self-assembly is saturated. Self-assemblies of all three dyes exhibit both lateral and longitudinal short-range order; N3 displays a particularly short coherence length along the TiO2 surface, with extensive structured disorder along the longitudinal direction. The operation of DSSC working electrodes would therefore seem to be dependent on a dye self-assembly that may exhibit several levels of structural granularity and dye aggregation effects.

Journal Keywords: dye-sensitized solar cell; X-ray reflectometry; Grazing-incidence X-ray scattering (GIXS); nanoaggregate size and separation; sensitization concentration; dye self-assembly; lateral and longitudinal short-range order; coherence length

Subject Areas: Materials, Chemistry, Energy


Instruments: I07-Surface & interface diffraction