Examination of Tethered Porphyrin, Chlorin, and Bacteriochlorin Molecules in Mesoporous Metal-Oxide Solar Cells

Abstract

The performance of five tetrapyrrole molecules as sensitizers in regenerative solar cells was evaluated. The tetrapyrroles form two sets. One set contains three meso-substituted porphyrins that differ only in the nature of their surface-binding tether: isophthalic acid, ethynylisophthalic acid, or cyanoacrylic acid. The other set includes the ethynylisophthalic acid tether attached to porphyrin, chlorin, and bacteriochlorin macrocycles, which contain zero, one, and two saturated pyrrole rings, respectively. Incident photon-to-current efficiency was measured for each sensitizer loaded onto a mesoporous TiO2 semitransparent electrode in a solar cell. The porphyrin bearing the cyanoacrylic acid tether gives the largest peak and integrated (350−900 nm) photocurrent density of the five tetrapyrrole molecules. For this sensitizer, a quasi-monochromatic power conversion efficiency of 21% was obtained at the Soret maximum (450 nm), along with a fill factor of 0.69. To elucidate the molecular origins of the effects of tether and macrocycle reduction on photocurrent production, the measured redox potentials and optical absorption spectra were analyzed in terms of the characteristics (energies and electron-density distributions) of the frontier molecular orbitals obtained from density functional theory calculations. Additionally, first-principle simulations were performed for the production of photocurrent by hypothetical planar and actual mesoporous films of each sensitizer under AM 1.5 solar irradiation. Collectively, the findings give fundamental insights into the factors that govern the observed differences in photocurrent production characteristics for the five tetrapyrrole sensitizers. In addition, the results provide a framework for further tuning of the properties of these molecules and related sensitizers to enhance solar-cell performance.

Ternary Porphyrinato HfIV and ZrIV Polyoxometalate Complexes

“…AFM studies of the compound on the ITO do not reveal large aggregates of the metalloporphyrin and a somewhat decreased rms roughness. Since the Zr(TPP) 2+ and Hf(TPP) 2+ complexes robustly bind surfaces, likely at defect sites and we remove unbound materials, the surface coverages are much less than coating of porphyrins such as tetracarboxyphenyl derivatives on ITO or TiO 2 surfaces by chemisorption 16,17,20,52. Relative to the surface, the horizontal orientation of the Zr and Hf complexes of TPP also diminishes the maximum potential coverage compared to the vertical orientation of the TCPP 52.…”

“…The efficiency of charge transport from molecules into semiconductors underpins a variety of hybrid molecular-semiconductor device architectures and other photonic materials. Charge transport efficiency is mediated by appropriate matching of molecular HOMO-LUMO gaps to semiconductor band gaps, the linker, and the proximity of the molecule 2,17,18,20,51. Metals that axially bind oxygen, e.g.…”

De NovoSynthesis of Gem-Dialkyl Chlorophyll Analogues for Probing and Emulating Our Green World

“…The chlorins in Scheme 87 that contain a gem-dimethyl group include the following: (1) the naturally occurring Bonellin; (2) 111f , prepared by Jacobi 243 (see Schemes 37–40 for other examples); (3) 202 , which bears an isophthalic acid moiety designed for incorporation in solar cells; 275,276 (4) 203a , which bears a single benzoic acid unit (10-position) and a p -tolyl group (5-position); 299 and (5) 203b , which bears a single phosphonic acid unit (10-position) and a p -tolyl group (5-position). 261 Chlorin 202 was prepared from H 2 C-T 5 M 10 by 15-bromination (neutral conditions) followed by Sonogashira coupling.…”

Introduction of carboxylic ester and acid functionalities to meso-tetrakis(pentafluorophenyl)porphyrin and their limited electronic effects on the chromophore

“…[17] Recently tested hydroporphyrins were promising but they were also prepared by multi-step, non-trivial total syntheses. [18] (Structures 1 and 2)…”