Photophysical Study on the Effect of the External Potential on NiO-Based Photocathodes

In the present study, we investigate the effects of the applied external potential on a dye-sensitized NiO photocathode by time-resolved photoluminescence and femtosecond transient absorption spectroscopy under operating conditions. Instead of the anticipated acceleration of photoinduced hole injection from dye into NiO at a more negative applied potential, we observe that both hole injection and charge recombination are slowed down. We cautiously assign this effect to a variation in OH- ion concentration in the inner Helmholtz plane of the electrochemical double layer with applied potential, warranting further investigation for the realization of efficient solar fuel devices.

Designing Efficient Metal-Free Dye-Sensitized Solar Cells: A Detailed Computational Study

The modulation of molecular characteristics in metal-free organic dyes holds significant importance in dye-sensitized solar cells (DSSCs). The D-π-A molecular design, based on the furan moiety (π) in the conjugated spacer between the arylamine (D) and the 2-cyanoacrylic acid (A), was developed and theoretically evaluated for its potential application in DSSCs. Utilizing linear response time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional, different donor and acceptor groups were characterized in terms of the electronic absorption properties of these dyes. All the studied dye sensitizers demonstrate the ability to inject electrons into the semiconductor's conduction band (TiO2) and undergo regeneration through the redox potential triiodide/iodide (I3-/I-) electrode. TDDFT results indicate that the dyes with CSSH anchoring groups exhibit improved optoelectronic properties compared to other dyes. Further, the photophysical properties of all dyes absorbed on a Ti(OH)4 model were explored and reported. The observed results indicate that bidentate chemisorption occurs between dyes and TiO4H5. Furthermore, the HOMO-LUMO energy gaps for almost all dye complexes are significantly smaller than those of the free dyes. This decrease of the HOMO-LUMO energy gaps in the dye complexes facilitates electron excitation, and thus more photons can be adsorbed, guaranteeing larger values of efficiency and short-circuit current density.

All-in-One Electric Double Layer Supercapacitors Based on CH3NH3PbI3 Perovskite Electrodes

Supercapacitors (SCs) are widely used energy storage devices in various applications that require instantaneous power supply and fast response times; however, the challenge for achieving high performance demands the continuous development and tailoring of electrode materials. Organic-inorganic halide perovskites (OIHPs) have recently received significant attention in electrochemical energy storage and conversion applications due to their unique properties including high charge carrier mobility, high mixed (electronic-ionic) conductivity, and presence of large oxygen vacancies. This study presents the fabrication and use of OIHPs based on methyl-ammonium lead iodide (CH₃NH₃PbI₃) and its Co²⁺- and Bi³⁺-substituted derivatives (CH₃NH₃Pb_1-x Co _x I₃ and CH₃NH₃Pb_1-x Bi _x I₃, respectively, where x = 0.1) as electrodes for SCs. SC devices were constructed symmetrically by sandwiching the synthesized electrode materials in a quasi-solid-state electrolyte between two TiO₂-coated FTO glasses. We discussed the optimization parameters (i.e., A-site doping, B-site doping, and controlling the stoichiometry of the anion and cation) to improve the electrochemical performance of the fabricated SCs. Furthermore, the effects of substitution ions (Co²⁺ and Bi³⁺) on the charge-discharge performance, energy and power density, defects, crystallinity, and microstructure were demonstrated. Electrochemical performances of the electrodes were analyzed by using CV, EIS, and GCPL techniques. The highest power density of 934.6 W/kg was obtained for Bi-substituted perovskite electrodes. Fabricated SC devices show good cyclability with 97.2, 96.3, and 86.6% retention of the initial capacitances after 50 cycles for pure, Co²⁺-substituted, and Bi³⁺-substituted perovskite electrodes, respectively.

Dye-sensitized solar cells strike back

Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. In recent years, DSCs and dye-sensitized photoelectrochemical cells (DSPECs) have experienced a renaissance as the best technology for several niche applications that take advantage of DSCs' unique combination of properties: at low cost, they are composed of non-toxic materials, are colorful, transparent, and very efficient in low light conditions. This review summarizes the advancements in the field over the last decade, encompassing all aspects of the DSC technology: theoretical studies, characterization techniques, materials, applications as solar cells and as drivers for the synthesis of solar fuels, and commercialization efforts from various companies.

Hydrogel Electrolytes Based on Xanthan Gum: Green Route towards Stable Dye-Sensitized Solar Cells

The investigation of innovative electrolytes based on nontoxic and nonflammable solvents is an up-to-date, intriguing challenge to push forward the environmental sustainability of dye-sensitized solar cells (DSSCs). Water is one of the best choices, thus 100% aqueous electrolytes are proposed in this work, which are gelled with xanthan gum. This well-known biosourced polymer matrix is able to form stable and easily processable hydrogel electrolytes based on the iodide/triiodide redox couple. An experimental strategy, also supported by the multivariate chemometric approach, is used here to study the main factors influencing DSSCs efficiency and stability, leading to an optimized system able to improve its efficiency by 20% even after a 1200 h aging test, and reaching an overall performance superior to 2.7%. In-depth photoelectrochemical investigation demonstrates that DSSCs performance based on hydrogel electrolytes depends on many factors (e.g., dipping conditions, redox mediator concentrations, etc.), that must be carefully quantified and correlated in order to optimize these hydrogels. Photovoltaic performances are also extremely reproducible and stable in an open cell filled in air atmosphere, noticeably without any vacuum treatments.

Flipping Molecules over on TiO2 Surfaces with Light and Electric Fields

Light excitation of the sensitizer [Ru(NH₃)₅(eina)](PF₆)₂, where eina is ethyl isonicotinate, anchored to anatase TiO₂ nanocrystallites interconnected in a mesoporous thin film and immersed in CH₃CN resulted in spectroscopic changes consistent with both excited-state injection and sensitizer reorientation, termed flipping. When the light irradiation was removed, the sensitizers flipped back over. Such flipping was absent when the carboxylic acid derivative of the sensitizer was utilized or when SnO₂/TiO₂ core/shell materials were employed in place of TiO₂. The flipping was attributed to the torque on the sensitizer in the electric field generated by the injected electrons. Pulsed light excitation was utilized to time-resolve flipping and charge recombination with this and the per-deuterated complex (ND₃)₅Ru^II(eina)|TiO₂. In all cases, charge recombination was more rapid when the oxidized sensitizer was flipped over, behavior consistent with stronger electronic coupling. Kinetic isotope effects of 26.7 and 0.12 were determined for charge recombination and for flipping, respectively. Spectro-electrochemical measurements showed that thermal reduction of TiO₂ with an applied potential also initiated flipping yet required much larger field strengths. The data show that the electric fields created at illuminated semiconductor interfaces are sufficient to reorientate molecules anchored to its surface.

Theoretical study on the influence of electric field direction on the photovoltaic performance of aryl amine organic dyes for dye-sensitized solar cells

It is very important to reveal the influence of different electric field directions on dye sensitizers.

Diverging surface reactions at TiO2- or ZnO-based photoanodes in dye-sensitized solar cells

Surface reactions of electrolyte additives and consequences for cell properties are studied and assigned to characteristics specific for both semiconductors.

Molecular Engineering of D-π-A Type of Blue-Colored Dyes for Highly Efficient Solid-State Dye-Sensitized Solar Cells through Co-Sensitization

A novel blue-colored organic donor-π-acceptor sensitizer, the so-called MKA16 dye, has been employed to construct solid-state dye-sensitized solar cells (ssDSSCs). Using 2,2',7-,7'-tetrakis( N, N-di- p-methoxyphenyl-amine) 9,9'-spirobifuorene (Spiro-OMeTAD) as hole-transport material, a good conversion efficiency of 5.8% was recorded for cells based on the MKA16 dye and a high photovoltage of 840 mV in comparison with 5.6% efficiency using the known (Dyenamo Blue) dye. By co-sensitization using the orange-colored D35 dye and MKA16 together, the solid-state solar cells showed an excellent efficiency of 7.5%, with a high photocurrent of 12.41 mA cm^-2 and open-circuit voltage of 850 mV. The results show that the photocurrent of ssDSSCs can be significantly improved by co-sensitization mainly attributed to the wider light absorption range contributing to the photocurrent. In addition, results from photo-induced absorption spectroscopy show that the dye regeneration is efficient in co-sensitized solar cells. The current results possible routes of improving the design of aesthetic and highly efficient ssDSSCs.

A small electron donor in cobalt complex electrolyte significantly improves efficiency in dye-sensitized solar cells

Photoelectrochemical approach to solar energy conversion demands a kinetic optimization of various light-induced electron transfer processes. Of great importance are the redox mediator systems accomplishing the electron transfer processes at the semiconductor/electrolyte interface, therefore affecting profoundly the performance of various photoelectrochemical cells. Here, we develop a strategy—by addition of a small organic electron donor, tris(4-methoxyphenyl)amine, into state-of-art cobalt tris(bipyridine) redox electrolyte—to significantly improve the efficiency of dye-sensitized solar cells. The developed solar cells exhibit efficiency of 11.7 and 10.5%, at 0.46 and one-sun illumination, respectively, corresponding to a 26% efficiency improvement compared with the standard electrolyte. Preliminary stability tests showed the solar cell retained 90% of its initial efficiency after 250 h continuous one-sun light soaking. Detailed mechanistic studies reveal the crucial role of the electron transfer cascade processes within the new redox system.

The electrolyte is an important component of dye-sensitized solar cells. Here, Hao et al. use an electron donor additive in the cobalt-based electrolyte, which speeds up the dye regeneration and slows down recombinations. The resulting devices are stable and more efficient than those without additive.

Supramolecular Hemicage Cobalt Mediators for Dye-Sensitized Solar Cells

A new class of dye-sensitized solar cells (DSSCs) using the hemicage cobalt-based mediator [Co(ttb)]2+/3+ with the highly preorganized hexadentate ligand 5,5'',5''''-((2,4,6-triethyl benzene-1,3,5-triyl)tris(ethane-2,1-diyl))tri-2,2'-bipyridine (ttb) has been fully investigated. The performances of DSSCs sensitized with organic D-π-A dyes utilizing either [Co(ttb)]2+/3+ or the conventional [Co(bpy)3 ]2+/3+ (bpy=2,2'-bipyridine) redox mediator are comparable under 1000 W m-2 AM 1.5 G illumination. However, the hemicage complexes exhibit exceptional stability under thermal and light stress. In particular, a 120-hour continuous light illumination stability test for DSSCs using [Co(ttb)]2+/3+ resulted in a 10 % increase in the performance, whereas a 40 % decrease in performance was found for [Co(bpy)3 ]2+/3+ electrolyte-based DSSCs under the same conditions. These results demonstrate the great promise of [Co(ttb)]2+/3+ complexes as redox mediators for efficient, cost-effective, large-scale DSSC devices.

Enhanced performance of dye-sensitized solar cells with dual-function coadsorbent: reducing the surface concentration of dye–iodine complexes concomitant with attenuated charge recombination

We introduce a dual-function coadsorbent in DSCs, that play a beneficial role in the recombination and iodine binds to the N719 dye.