Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 11, Issue 18, Pages 16474-16489Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.8b21414
Keywords
porphyrin; NIR dyes; dye-sensitized solar cells; proaromatic; aggregate analysis
Funding
- National Science Foundation [1539035, 1455167]
- Office of Naval Research Young Investigator Program [N00014-18-1-2448]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1455167] Funding Source: National Science Foundation
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Porphyrins are attractive chromophores for application in dye-sensitized solar cells (DSCs), as judicious tuning of donor-acceptor properties can enable excellent near-infrared (NIR) absorption and exceptional device performance. Here, we report a porphyrin-based dye (SM85) conjugated to the planar strong electron donor, indolizine, designed to extend absorption further into the NIR region by inducing pi-pi interactions such as head-to-tail dye aggregation. The optoelectronic consequences of indolizine incorporation in SM85 include raising the ground-state oxidation potential and broadening and red-shifting ultraviolet-visible-NIR absorptions, along with increased molar absorptivity when compared to the dye SM315. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations confirm the push-pull character of SM85, which features an overlap of frontier occupied and unoccupied orbitals. Steady-state spectrophotometric analyses reveal the presence of solution aggregates via absorption and emission spectroscopies. Aggregate modes were probed by DFT and TD-DFT analyses, and plausible models are presented. SM85-based DSC devices demonstrate a 5.7% power conversion efficiency (PCE) at full sun (7.4% PCE at 10% sun) with an exceptional improvement to the incident photon-to-current conversion onset at similar to 850 nm. Current dynamics measurements, time-correlated single photon counting, and computational analyses are used to better understand device performances. This study puts forward a novel intramolecular charge-transfer porphyrin system with a dramatic shift into the NIR region, as is needed for nonprecious metal-based sensitizers, and provides an example of controlled, donor-acceptor-mediated aggregation as a complementary strategy to traditional donor-acceptor modifications to single-molecule pi-systems in accessing enhancements in long wavelength light harvesting in molecular-based optoelectronic devices.
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