An investigation of the roles furan versus thiophene π-bridges play in donor-π-acceptor porphyrin based DSSCs

Photochromic naphthopyran dyes incorporating a benzene, thiophene or furan spacer: effect on photochromic, optoelectronic and photovoltaic properties in dye-sensitized solar cells

We recently demonstrated that diaryl-naphthopyran photochromic dyes are efficient for sensitization of TiO₂ mesoporous electrodes, thus allowing the fabrication of photo-chromo-voltaic cells that can self-adapt their absorption of light and their generation of electricity with the light intensity. Herein we report the synthesis, the characterisation of two novel photochromic dyes based on diaryl-naphthopyran core i.e NPI-ThPh and NPI-FuPh for use in Dye Sensitized Solar Cells (DSSCs). Compared to our reference dye NPI, the molecules only vary by the nature of the spacer, a thiophene or a furan, connecting the photochromic unit and the phenyl-cyano-acrylic acid moiety used as the anchoring function. We found that swapping a phenyl for a thiophene or a furan leads to an improvement of the absorption properties of the molecules both in solution and after grafting on TiO₂ electrodes, however their photochromic process becomes not fully reversible. Despite better absorption in the visible range, the new dyes show poorer photochromic and photovoltaic properties in devices compared to NPI. Thanks to UV-Vis spectroscopy, DFT calculation, electrical characterization of the cells, and impedance spectroscopy, we unravel the factors limiting their performances. Our study contributes to better understand the connection between photochromic and photovoltaic properties, which is key to develop better performing molecules of this class.

Two multifunctional benzoquinone derivatives as small molecule organic semiconductors for bulk heterojunction and perovskite solar cells

Two novel quinone derivatives (NN3 and NN4) were synthesized in this work and they were characterized to be used as small organic semiconductor molecules in different types of photovoltaic applications. To make accessible compounds, three simple steps were followed to prepare NN3 and NN4 compounds. Furthermore, energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were determined for the computationally optimized models of the investigated compounds. The obtained optical and electrochemical results of this work indicated that NN3 and NN4 compounds were good candidates for application in the fields of bulk heterojunction (BHJ) and perovskite solar cells. Indeed, investigating new energy resources has been seen an important topic of research for producing clean energies and portable storage systems.

Synthesis, Optical Properties, and Electrochemical Behavior of 5,10,15,20-Tetraaryl-5,15-diazaporphyrin-Amine Hybrids

This work reports a series of covalently linked hybrids comprising 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (M-TADAP; M = Ni, Zn, Cu) and amines. M-TADAP-amine hybrids were prepared via the metal-templated cyclization of the corresponding metal(II)-dipyrrin complexes and redox reactions on the DAP unit. In the UV/vis/near-IR absorption spectra of the hybrids containing an 18π-electron DAP ring, broad charge-transfer bands were observed, reflecting the electron-donating property of the para-aminophenyl groups and the electron-accepting property of the 18π TADAP dication. The electrochemical behavior of the M-TADAP-amine hybrids was strongly dependent on the structure of the peripheral amine units. Further electrochemical oxidation of the hybrids bearing N-Ph groups conceivably generated amine-centered radicals, which sequentially underwent irreversible coupling to form benzidine-linked M-TADAP polymer films. The Ni-TADAP-benzidine polymer exhibited the electric conductivity of 1×10^-3  S m^-1 .

Electronic and optical properties' tuning of phenoxazine-based D-A2-π-A1 organic dyes for dye-sensitized solar cells. DFT/TDDFT investigations

Modulation of molecular features of metal free organic dyes is important to present sensitizers with competing electronic and optical properties for dye sensitized solar cells (DSSCs). The D-A₂-π-A₁ molecular design based on phenothiazine skeleton (D) connected with benzothiadiazole (A₂) linked with furan π-spacer and acceptor unit of cynoacrylic acid (A₁) were fabricated and examined theoretically for possible use as DSSCs. Density functional theory (DFT) and time dependent density functional theory TDDFT were used to study the effect of additional donors on the photophysical properties of the dyes. Eight (8) different donor subunits were introduced at C7 of phenoxazine based dye skeleton to extend the π-conjugation, lower HOMO-LUMO gap (E_g) and improve photo-current efficiency of the dye sensitizer. All the dye sensitizers (except P3 and P4) exhibited capability of injecting electrons into the conduction band of the semiconductor (TiO₂) and regenerated via redox potential (I⁻/I₃^-) electrode. Attachment of 2-hexylthiophene (P2) remarkably lowered the E_g, extended π-electron delocalization, hence, gives higher absorption wavelength (λ_max) at 752 nm. The donor subunit containing 2-hexylthiophene (P2) presented the best chemical hardness, open circuit voltage (V_oc), and other comparable electronic properties, making P2 the best DSSC candidate amongst the optimized dyes. The reported dyes would be interesting for further experimental research.

Bis(μ-thiolato)-dicopper Containing Fully Spin Delocalized Mixed Valence Copper-Sulfur Clusters and Their Electronic Structural Properties with Relevance to the CuA Site

With aromatic and aliphatic thiol-S donor Schiff base ligands, the copper-sulfur clusters, [(L1)₈Cu^I₆Cu^II₂](ClO₄)₂·DMF·0.5CH₃OH (1) and [(L2)₁₂Cu^I₅Cu^II₁₁(μ₄-S)(μ₄-O)₆](ClO₄)·4H₂O, respectively, have been reported ( Chem. Commun. 2017, 53, 3334); HL1/HL2 are 2-(((3-methylthiophen-2-yl)methylene)amino)benzene/ethanethiol). Complex 1 comprises a wheel shaped Cu₈S₈ framework, made up of interlinked Cu₂{μ-S(R)}₂ units. To understand the properties with relevance to the Cu_A site and to check whether self-assembly generates similar type clusters to 1, three complexes, [(L3)₈Cu^I₆Cu^II₂](ClO₄)₂·(C₂H₅)₂O·2.5H₂O (2), [(L3^Cl)₈Cu^I₆Cu^II₂](ClO₄)₂·1.25(C₂H₅)₂O·1.25CH₃OH·2H₂O (3), and [(L3^CF3)₈Cu^I₆Cu^II₂](ClO₄)₂·2(C₂H₅)₂O·H₂O (4) have been synthesized with supporting ligands HL3^X (HL3 = 2-((furan-2-ylmethylene)amino)benzenethiol when X = -H; X = -Cl or -CF₃ para to thiol-S are HL3^Cl and HL3^CF3 ligands, respectively). The X-ray structures of 3 and 4 feature a similar Cu₈S₈ architecture to 1. The spectroscopic properties and the X-ray structures revealed that 2-4 are fully spin delocalized mixed valence (MV) of class-III type clusters. The structural parameters of the N₂Cu₂{μ-S(R)}₂ units of 3 and 4 closely resemble those of the MV binuclear Cu_A site. With the aid of UV-vis-NIR, EPR, and spectroelectrochemical studies, the electronic properties of these complexes have been described in comparison with the MV model complexes and Cu_A site.

Bis(4′-tert-butylbiphenyl-4-yl)aniline (BBA)-substituted A3B zinc porphyrin as light harvesting material for conversion of light energy to electricity

Limited synthetic steps via low-cost starting materials are needed to develop large-scale light-active materials for efficient solar cells. Here, novel bis(4[Formula: see text]-tert-butylbiphenyl-4-yl)aniline (BBA) based A3B zinc porphyrin (GB) is synthesized and applied as a light harvesting/electron injection material in dye-sensitized solar cells. The GB sensitizer was characterized by various spectroscopic techniques and the optimized device shows [Formula: see text] of 10.98 ± 0.37 mA/cm2 and power conversion efficiency (PCE) of 3.34 ± 0.26%. In addition, performance is enhanced up to ∼3.9% by the addition of co-adsorbent 3a,7a-dihydroxy-5b-cholic acid (chenodeoxycholic acid, CDCA) to minimize [Formula: see text]-[Formula: see text] staking of the planar porphyrin macrocycles. These results demonstrate that novel broad-absorbing light-active material (GB) could be used for indoor solar panels.

Coplanar Donor-π-Acceptor Dyes Featuring a Furylethynyl Spacer for Dye-Sensitized Solar Cells

Coplanar metal-free organic dyes featuring a furylethynyl spacer with different donor residues (MeO-, MeS-, and Me₂N-) have been synthesized. Density functional theory (DFT) calculations predicted that the Me₂N- residue would facilitate more effective charge transfer from donor to acceptor than the MeO- and MeS- residues. In agreement with DFT calculations, the dye-sensitized solar cells (DSSCs) fabricated with the Me₂N- functionalized dye exhibited the best power conversion efficiency (η), 2.88%. Furthermore, the effect of the furan spacer on the photophysical properties and DSSC parameters are discussed in comparison to a previously reported thiophene counterpart.

Effect of furan π-spacer and triethylene oxide methyl ether substituents on performance of phenothiazine sensitizers in dye-sensitized solar cells

Synthesis and characterization of three phenothiazine dyes inspired by literature dye EO3 improving absorption properties and photovoltaic performance in DSSCs.

J, Pradhan SC, Lingamoorthy S, P. R. N, M. V. C, Mishra RK, K. N. NU, John J, Soman S. Indolo[3,2-b]indole donor-based D–π–A dyes for DSCs: investigating the role of π-spacers towards recombination

A detailed investigation of recombination, employing novel indolo[3,2-b]indole donor-based organic D–π–A dyes with variable π-spacers, using various perturbation techniques.

Iodine binding with thiophene and furan based dyes for DSCs

Donor–π-bridge–acceptor dyes with thiophene have been shown to bind I₂ leading to diminished dye-sensitized solar cell performances relative to furan based analogues.