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 π–π 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 ∼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 π-systems in accessing enhancements in long wavelength light harvesting in molecular-based optoelectronic devices.
Metal-free bis-cyclopentadithiophene-based molecular sensitizers with varying halogens (Cl, Br, and I) installed at a terminal position in conjugation with the dye frontier molecular orbital π-system are studied in combination with two cobalt redox shuttles (RSs): with and without a nonmetal-coordinated nitrogen atom (pyrazine or pyridine) accessible to the halide-decorated dyes. This systematic study employs UV−vis absorption, cyclic voltammetry, density functional theory calculations, and nanosecond transient absorption spectroscopy to probe the influence of possible halogen-bonding between the dyes and the pyrazine-based RS on electron-transfer reactions and effects on dye-sensitized solar cell performances. The results of this study imply a possible halogen-bonding event occurring between the halogenated dyes and the halogen binding RS with substantial effects on electrontransfer reaction rates.
“The Hagfeldt donor” is a bulky triarylamine building block with four alkyl chains in a 3‐dimensional arrangement that is used with organic dyes in dye‐sensitized solar cells (DSCs) in over 140 publications. Many of the highest performing DSC devices in literature make use of this group due to exceptional TiO2 surface protection properties, which slows recombination of electrons in TiO2 with the electrolyte. Importantly, record‐setting cobalt and copper redox shuttle‐based DSCs require exceptional surface protection to slow a facile recombination of electrons to these positively charged redox shuttles. Several syntheses have emerged for the Hagfeldt donor due to the need for iterative aryl–halide cross‐ coupling reactions complicating a straightforward route. Six synthetic strategies found in literature are described along with the challenges of each route. A recent method that has been put forward in the literature as a scalable, regioisomerically pure route is highlighted.
Near-infrared-absorbing organic dyes are critically needed in dye-sensitized solar cells (DSCs). Thieno[3,4-b]pyrazine (TPz) based dyes can access the NIR spectral region and show power conversion efficiencies (PCEs) of up to 8.1 % with sunlight being converted at wavelengths up to 800 nm for 17.6 mA cm of photocurrent in a co-sensitized DSC device. Precisely controlling dye excited-state energies is critical for good performances in NIR DSCs. Strategies to control TPz dye energetics with stronger donor groups and TPz substituent choice are evaluated here. Additionally, donor size influence versus dye loading on TPz dyes is analyzed with respect to the TiO surface protection designed to prevent recombination of electrons in TiO with the redox shuttle. Importantly, the dyes evaluated were demonstrated to work well with low Li concentration electrolytes, with iodine and cobalt redox shuttle systems, and efficiently as part of co-sensitized devices.
The bulky triarylamine group commonly referred to as the "Hagfeldtd onor" is ak ey buildingb lock found in many of the organic dyes used in dye-sensitized applications such as dyesensitized solar cells (DSCs). This building block has gained popularity owing to its presence in many of the best-performing DSC devicesr eported to date, which use dyes containing this donorg roup. The Hagfeldt donor provides ad esirable 3dimensionals tructure that aids in surface protection of electrons injected into the semiconductor from oxidants in the electrolyte, allowing for record-setting cobalt-and copperbased redoxs huttles to be utilized more frequently.H owever, the synthesiso ft his molecule has provenu nreliable form any routes. This study concerns an ovel, reliable and scalable fivestep synthesis of the Hagfeldt donor.Supporting Information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
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