Fabrication and performance of all-solid-state dye-sensitized solar cells using synthetic carboxylated and pyridylated chlorophyll derivatives

Highly Efficient DSSCs Sensitized Using NIR Responsive Bacteriopheophytine-a and Its Derivatives Extracted from Rhodobacter Sphaeroides Photobacteria

Employing naturally extracted dyes and their derivatives as photosensitizers towards the construction of dye-sensitized solar cells (DSSCs) has been recently emerging for establishing sustainable energy conversion devices. In this present work, Rhodobacter Sphaeroides Photobacteria (Rh. Sphaeroides) was used as a natural source from which Bacteriopheophytine-a (Bhcl) dye was extracted. Further, two cationic derivatives of Bhcl, viz., Guanidino-bacteriopheophorbide-a (Gua-Bhcl) and (2-aminoethyl)triphenylphosphono-bacteriopheophorbide-a (2AETPPh-Bhcl) were synthesized. The thus obtained Bhcl, Gua-Bhcl and 2AETPPh-Bhcl were characterized using liquid chromatography-mass spectrometry (LC-MS) and their photophysical properties were investigated using excitation and emission studies. All three near-infrared (NIR) responsive dyes were employed as natural sensitizers towards the construction of DSSC devices, using platinum as a photocathode, dye-sensitized P25-TiO2 as a photoanode and I-/I3- as an electrolyte. DSSCs fabricated using all three dyes have shown reasonably good photovoltaic performance, among which 2AETPPh-Bhcl dye has shown a relatively higher power conversion efficiency (η) of 0.38% with a short circuit photocurrent density (JSC) of 1.03 mA cm-2. This could be attributed to the dye's natural optimal light absorption in the visible and NIR region and uniform dispersion through the electrostatic interaction of the cationic derivatives on the TiO2 photoanode. Furthermore, the atomic force microscopy studies and electrochemical investigations using cyclic voltammetry, electrochemical impedance spectroscopy and Bode's plot also supported the enhancement in performance attained with 2AETPPh-Bhcl dye.

Surfactant-Free Green Synthesis of Au@Chlorophyll Nanorods for NIR PDT-Elicited CDT in Bladder Cancer Therapy

The facile and straightforward fabrication of NIR-responsive theranostic materials with high biocompatibility is still an unmet need for nanomedicine applications. Here, we used a natural photosensitizer, iron chlorophyll (Chl/Fe), for the J-aggregate template-assisted synthesis of Au@Chl/Fe nanorods with high stability. The assembly of a high amount of Chl/Fe J-aggregate onto the Au surface enabled red-NIR fluorescence for monitoring and tracking residential tumor lesions. The Chl/Fe moieties condensed on the nanorods could change the redox balance by the photon induction of reactive oxygen species and attenuate iron-mediated lipid peroxidation by inducing a Fenton-like reaction. After conjugation with carboxyphenylboronic acid (CPBA) to target the glycoprotein receptor on T24 bladder cancer (BC) cells, the enhanced delivery of Au@Chl/Fe-CPBA nanorods could induce over 85% cell death at extremely low concentrations of 0.16 ppm_[Au] at 660 nm and 1.6 ppm_[Au] at 785 nm. High lipid peroxidation, as shown by BODIPY staining and GSH depletion, was observed when treated T24 cells were exposed to laser irradiation, suggesting that preliminary photodynamic therapy (PDT) can revitalize Fenton-like reaction-mediated chemodynamic ferroptosis in T24 cells. We also manipulated the localized administration of Au@Chl-Fe combined with PDT at restricted regions in orthotopic tumor-bearing mice to cure malignant BC successfully without recurrence. By intravesical instillation of the Au@Chl/Fe-CPBA nanorods, this localized treatment could prevent the material from entering the systemic circulation, thus minimizing systemic toxicity. Upon activating NIR-PDT-elicited chemodynamic therapy, ultrasound imaging revealed almost complete tumor remission. Anti-tumor efficacy and survival benefit were achieved with a green photosensitizer.

Substituted Methylenation at the 132 -Position of a Chlorophyll-a Derivative via Mixed Aldol Condensation, Optical Properties of the Synthetic Bacteriochlorophyll-d Analogs, and Self-aggregation of Their Zinc Complexes

Chlorophyll-a derivatives possessing a substituted methylene group at the 13² -position were prepared by the mixed aldol condensation of methyl 3-hydroxymethyl-pyropheophorbide-a with aldehydes bearing a methyl, p-nitro/cyanophenyl, or pentafluorophenyl group. Their electronic absorption spectra were dependent on the substituents at the methylene terminal. The Soret bands were broadened with increasing the group electronegativity of the substituents, which was ascribable to the charge transfer from the core chlorin to the peripheral substituent in a molecule. Although their Qy absorption and fluorescence emission bands resembled each other, the emission intensities decreased with an increase in the electronegativity because of the intramolecular electron transfer quenching. Some of their zinc complexes self-aggregated in a less polar organic solvent to give red-shifted and broadened absorption bands with intense circular dichroism couplets, which were similar to those of bacteriochlorophyll-c/d aggregates in natural chlorosomes as the main light-harvesting antennas of green photosynthetic bacteria and their models. The J-aggregation was suppressed with an enhancement in the size of the 13² -substituents.

Chlorophyll Derivative-Sensitized TiO2 Electron Transport Layer for Record Efficiency of Cs2AgBiBr6 Double Perovskite Solar Cells

The power conversion efficiency (PCE) of Cs₂AgBiBr₆-based perovskite solar cells (PSCs) is still low owing to the inherent defects of Cs₂AgBiBr₆ films. Herein, we demonstrate a carboxy-chlorophyll derivative (C-Chl)-sensitized mesoporous TiO₂ (m-TiO₂) film as an electron transport layer (ETL) to enhance and extend the absorption spectrum of Cs₂AgBiBr₆-based PSCs. The C-Chl-based device achieves a significantly improved PCE, exceeding 3% for the first time, with an increase of 27% in short-circuit current density. Optoelectronic investigations confirm that the introduction of C-Chl reduces the defects, accelerates the electron extraction, and suppresses charge recombination at the interface of ETL/perovskite. Moreover, the unencapsulated PSCs display restrained hysteresis and great stability under ambient conditions.

In Depth Analysis of Photovoltaic Performance of Chlorophyll Derivative-Based "All Solid-State" Dye-Sensitized Solar Cells

Chlorophyll a derivatives were integrated in "all solid-state" dye sensitized solar cells (DSSCs) with a mesoporous TiO2 electrode and 2',2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene as the hole-transport material. Despite modest power conversion efficiencies (PCEs) between 0.26% and 0.55% achieved for these chlorin dyes, a systematic investigation was carried out in order to elucidate their main limitations. To provide a comprehensive understanding of the parameters (structure, nature of the anchoring group, adsorption …) and their relationship with the PCEs, density functional theory (DFT) calculations, optical and photovoltaic studies and electron paramagnetic resonance analysis exploiting the 4-carboxy-TEMPO spin probe were combined. The recombination kinetics, the frontier molecular orbitals of these DSSCs and the adsorption efficiency onto the TiO2 surface were found to be the key parameters that govern their photovoltaic response.