Dye-sensitized Solar Cells Devices Research Articles

Rational Design of Facile and Low‐Cost Construction of Carbon‐Based Dye‐Sensitized Solar Cells using Garcinia Mangostana L. as a Photosensitizer

Research on solar cell devices is not only always related to how to obtain high power conversion efficiency (PCE), but also other factors need to be fully considered, such as the cost and their ecofriendliness. In this present research, a low‐cost and ecofriendly dye‐sensitized solar cell (DSSC) is being developed using a graphite‐based nanocomposite and an unusual plant extract (Garcinia mangostana L.) as the dye photosensitizer. A rational design on how to use graphite as a photoanode and counter electrode (CE) in DSSC is carried out by combining the graphite with ZnO and multiwalled carbon nanotube (MWCNT), respectively. It is observed that graphite acts as a matrix for ZnO and MWCNT to make these nanocomposites have very appropriate optoelectronics and catalytic properties compared to the control sample. Therefore, they could serve as an excellent photoanode and CE, respectively. It is also expected that the anthocyanin absorption in Garcinia mangostana L. dye which is found in the visible light range can efficiently absorb photons, thus supporting the enhancement of photovoltaic performance of the DSSC. The generated voltage (V) and current (I) from light irradiation using commercial lamps are higher compared to halogen lamps, indicating that the obtained DSSC has potential as indoor powered devices. It is believed that our study can shed light on the development of DSSC using low‐cost material graphite as the main component for the realization of low‐cost DSSC devices.

Submicron-scale Au-decorated TiO2 mesoporous spheres for enhanced photon harvesting in DSSCs through near-field enhancement, light scattering, and dye loading

Light harvesting materials are crucial for capturing the sunlight in a device such as a solar cell for better efficiency. In this study, we developed high surface area, submicron-sized TiO2 spheres (MTS) incorporated with anisotropic Au nanoparticles (Au_MTS) to create highly light-absorbing photoanodes for enhanced dye-sensitized solar cell (DSSC) efficiency. The high surface area of MTS (∼125 m2/g) allows for increased dye-loading, while their submicron size (150–300 nm) provides superior light-scattering capabilities for significantly enhancing the photoanode’s light absorption. Furthermore, incorporating of anisotropic Au nanoparticles enables broadband surface plasmon resonance (SPR) coupling, synergistically boosting photon harvesting in the Au_MTS photoanodes. The interconnected tiny TiO2 nanoparticle network in MTS supports charge carrier generation and transport, providing ample sites for dye adsorption and efficient electron pathways. Au_MTS with varying amounts of Au nanoparticles synthesized by a greener microwave-assisted synthesis method and DSSC devices were fabricated and compared with devices made from pristine MTS and P25 nanoparticles. The optimal Au_MTS device, containing ∼1.3 wt% Au nanoparticles, achieved a maximum power conversion efficiency (PCE) of ∼7.7%, representing improvements of ∼40% and ∼60% over pristine MTS (PCE of ∼5.2%) and P25 nanoparticles (PCE of ∼4.71%), respectively. Overall, this work demonstrates the effectiveness of plasmonic mesoporous photoanodes in enhancing DSSC performance through improved photo response, light scattering, and dye loading.

Far-red active squaraine dye-sensitized photoanode for dye-sensitized solar cells with a copper (II/I) electrolyte

In dye-sensitized solar cells (DSSC), controlling the dye-aggregation on TiO2 and charge recombination between electrons present in TiO2 and electrolyte can be achieved by wrapping the long alkyl groups around the dye structure and further introducing bulky donor on the dye is a potential approach to enhance both the open-circuit potential and short-circuit current parameters. Additionally, bulky donor containing dye structures modulates the photophysical and electrochemical properties of the sensitizer which helps reducing the over potentials required for the dye regeneration process by utilizing a multidentate ligand containing [Cu(tme)]2+/+ and I−/I3− redox electrolytes. Hagfeldt donor appended far-red NIR active unsymmetrical squaraine dye (SQ-HF) has been designed, synthesized, and characterized. SQ-HF dye showed an intense absorption at 676 nm (ε 1.7 × 105 M−1cm−1). Photophysical and electrochemical studies indicated that the LUMO and HOMO energy levels of the SQ-HF dye were suited for charge injection (from the LUMO of the dye to the conduction band of TiO2) and dye-regeneration processes, respectively. The DSSC device efficiency of 5.15 % (JSC of 10.83 mA/cm2 and VOC of 0.690 V) has been achieved for SQ-HF dye by utilizing a literature reported [Cu(tme)]2+/+ and 4.11 % (JSC of 8.74 mA/cm2 and VOC of 0.702 V) in I−/I3− redox shuttles, respectively.

Enhanced Efficiency of Dye-Sensitized Solar Cells by Controlled Co-Adsorption Self-Assembly of Dyes.

Single dyes typically exhibit limited light absorption in dye-sensitized solar cells (DSSCs). Thus, cosensitization using two or more dyes to enhance light-harvesting efficiency has been explored; however, the aggregation of dyes can adversely affect electron injection capabilities. This study focused on the design and synthesis of three dyes with a common carbazole donor for DSSCs: DZ102, TZ101, and JM102. JM102 broadens the absorption spectrum by replacing the benzoic acid electron acceptor of TZ101 with acetylenic benzoic acid. A cosensitized DSSC device based on CO-1 [DZ102:TZ101 = 1:1 (50 μM:50 μM)] achieved a short-circuit current density of 19.4 mA/cm2 and a power conversion efficiency of 10.9%. For the first time, the molecular interactions between the dyes in the photoanode were demonstrated using cyclic voltammetry, which revealed the presence of intermolecular forces. Adsorption kinetics further indicated that these forces promoted the self-assembly of dyes during adsorption, which resulted in a cosensitization adsorption amount greater than the sum of the individual dye adsorptions. This study provides novel insights into the selection of cosensitizing dyes for DSSCs.

Exploration of the structural and electrical characteristics and solar cell applications of an electrolyte membrane derived from acacia gum

The natural and eco-friendly solid-state electrolytes were prepared using varying concentrations (wt%) of ZnSO4.7H2O salt and pure acacia gum through the solution cast method. Multiple analytical methods were employed to characterize the resulting acacia gum electrolyte samples. XRD analysis confirmed the increased presence of the amorphous phase with the introduction of salt. FTIR analysis explored the formation of interlinking bands and their complex nature upon salt incorporation. The ionic conductivity was found from room temperature (RT) to 100 °C range. The optimized high ionic conductivity value was found to be 1.11 × 10−4 S/cm at 100 °C for the electrolyte composed of 70 wt% acacia gum and 30 wt% ZnSO4.7H2O, while at RT it was 1.06 × 10−5 S/cm for the same composition. Activation energy values fell within the 0.6–0.92 eV range for all samples. Complex dielectric (real and imaginary) and complex electric modulus analyses were conducted. Dielectric permittivity and electrical modulus analyses revealed a significant interaction between the segmental movements of acacia gum and salt ions. Ionic relaxation processes were explored in terms of conductivity relaxation time using the electrical modulus. The presence of a long tail in the complex dielectric modulus study indicated that the acacia-based solid electrolyte displayed favorable capacitance properties. Further, the Solar Cell (dye-sensitized solar cell) device was fabricated with (Acacia gum + ZnSO4.7H2O) electrolyte. The current density-voltage (J-V) characteristics of the prepared device were investigated. The outstanding results were optimized in the present work, Voc = 0.81 V, Jsc = 9.56 mA/cm2, Fill Factor of 0.67, and optimum power conversion efficiency ƞ = 5.17 % for the electrolyte composed of 70 wt% acacia gum and 30 wt% ZnSO4.7H2O device.

Spectral properties and photophysical processes of triphenylamine-porphyrin-pyrimidine triads

Porphyrins have attracted considerable attention as an important family of photosensitizers used for dye-sensitized solar cells (DSSCs). In this work, a novel triphenylamine-porphyrin-pyrimidine triad with a triple bond linkage was synthesized and characterized. The sensitizer presents broad absorption in solution and on TiO2 films across the UV-Vis region benefiting from the extended conjugation. The acetenyl [Formula: see text]-conjugated bridge stimulates the photoinduced electron transfer (PET) process and brings a charge-separated state lifetime of around 4 μs. DSSC devices based on the sensitizer achieve a power conversion efficiency (PCE) of 3.77% thanks to the prolonged charge-separated state lifetime and suppressed charge recombination. The understanding of the structural, optical, and electrochemical properties of triphenylamine-porphyrin-pyrimidine triads provides new insights into the rational design of porphyrin sensitizers for various applications.

Fabrication of binder-free TiO2 P 25 films on flexible PET/ITO substrate for photoanode in dye-sensitized solar cells

In this work, TiO2 P 25 films for photoanode in dye-sensitized solar cells (DSSCs) have been fabricated using a flexible PET/ITO substrate with a low-temperature heating technique. Ammonium hydroxide/ethanol solution was used as an alternative binding agent to fabricate TiO2 paste, which can be removed at low-temperature heating. The conventional screen print method is still used in DSSC fabrication because it is a very cheap and easy technique. A hot-pressing method is also used to improve the quality of TiO2 films and the performance of DSSCs. The encapsulation technique used in the assembly of DSSC is expected to increase the stability of DSSC devices to prevent electrolyte leakage. The resulting TiO2 film shows the highest DSSC performance using the hot-pressing and encapsulation method with PCE 0.29%. The encapsulation technique increased the stability of DSSC devices with more extended durability than without encapsulation.

Conformational and environmental effects on the electronic and vibrational properties of dyes for solar cell devices.

The main challenge for solar cell devices is harvesting photons beyond the visible by reaching the red-edge (650-780nm). Dye-sensitized solar cell (DSSC) devices combine the optical absorption and the charge separation processes by the association of a sensitizer as a light-absorbing material (dye molecules, whose absorption can be tuned and designed) with a wide band gap nanostructured semiconductor. Conformational and environmental effects (i.e., solvent, pH) can drastically influence the photophysical properties of molecular dyes. This study proposes a combined experimental and computational approach for the comprehensive investigation of the electronic and vibrational properties of a unique class of organic dye compounds belonging to the family of red-absorbing dyes, known as squaraines. Our focus lies on elucidating the intricate interplay between the molecular structure, vibrational dynamics, and optical properties of squaraines using state-of-the-art density functional theory calculations and spectroscopic techniques. Through systematic vibrational and optical analyses, we show that (i) the main absorption peak in the visible range is influenced by the conformational and protonation equilibria, (ii) the solvent polarity tunes the position of the UV-vis absorption, and (iii) the vibrational spectroscopy techniques (infrared and Raman) can be used as informative tools to distinguish between different conformations and protonation states. This comprehensive understanding offers valuable insights into the design and optimization of squaraine-based DSSCs for enhanced solar energy conversion efficiency.

Influence of functionalized diketopyrrolopyrrole sensitizer on the performance of CdS nanowire based-DSSC applications

Synthesis of chromophore (E)-2-(2-(2-(5-(2,5-bis(2-ethylhexyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6 tetrahydropyrrolo [3,4-c] pyrrol-1-yl) thiophen-2-yl) vinyl)-4H-chromen-4 ylidene) malononitrile (DPP-CM-CN) has been designed and achieved in multistep reaction strategy. The experimental, photophysical and electrochemical properties along with theoretical calculations were explored. DPP-CM-CN dye was – chemically anchored on CdS nanowires (NWs) to investigate its influence on the dye-sensitized solar cell (DSSC) applications. Under the illumination of standard sunlight conditions, the photovoltaic performance of DPP-CM-CN based CdS nanowire device displayed a power conversion efficiency (PCE) of 0.38 %, which is 3.30 times higher as compared to a bare CdS nanowire (0.115 %) based DSSC device; ascribed to the dye loading time on CdS nanostructures. The present results suggest the potential ability of DPP-CM-CN to enhance DSSC device efficiency and reveal the importance of dye molecules in device fabrication, a key step towards the development of DSSC technology.

Graphene oxide doping in tropical almond (terminalia catappa L.) fruits extract mediated green synthesis of TiO2 nanoparticles for improved DSSC power conversion efficiency

The power conversion efficiency (PCE) of a dye-sensitized solar cell (DSSC) device depends on its semiconductor characteristics. Titanium dioxide (TiO2) nanoparticles are a semiconductor material commonly used in the DSSC device whose characteristics depend on the synthesis process. There are many routes to synthesize TiO2, however, they typically involve hazardous approaches, which may cause risk to the environment. Green synthesis is an environmentally friendly alternative method using ecological solvents that eliminates toxic waste and reduces energy consumption. In this work, tropical almond (Terminalia catappa L.) was used as a natural capping agent in the green synthesis to control the growth of TiO2. In addition, graphene oxide (GO) was used as a dopant to increase the performance of DSSC device. The results are convincing, in which the addition of 0.0017 % GO doping in tropical almond extract mediated green synthesis of TiO2 improved the PCE from 0.85 % to 1.72 %. These results suggest that GO-modified TiO2 nanoparticles green synthesized using tropical almond extract have great potential in the fabrication of DSSC devices with good PCE, low cost, and low environmental impact.

Effects of Several Auxiliary Acceptors and Anchoring Groups on Charge Transfer and Photophysical Properties of D-A-π-A Type DSSCs: A DFT Study.

In this paper, we performed theoretical studies on the twelve D-A-π-A type organic dyes (G-1 ~ G-3, M-1 ~ M-3, J-1 ~ J-3, and S-1 ~ S-3) with 9-phenylcarbazole as the electron donor in anticipation of the application of these dyes in dye-sensitized solar cells (DSSCs). DFT and TD-DFT methods are applied to investigate in detail the molecular geometries, frontier molecular orbitals (FMOs), absorption spectra, charge density difference (CDD), and transition density matrix (TDM) of several dyes. The results show that the M-series (M-1 ~ M-3) dyes have the largest dihedral angles between the electron donor and the auxiliary acceptor and also has the largest energy gaps in HOMO-LUMO orbitals, which greatly reduces the charge transfer efficiency. Finally, the UV-Vis absorption spectra inferred that the anchoring groups modified with o-nitrobenzoic acid (G-3, M-3, J-3, S-3) can red-shift the absorption peaks of the dyes, which results in higher light-harvesting efficiency and improves the power conversion efficiency of DSSCs. Overall, all of these dyes contribute to the improvement of photovoltaic power conversion efficiency and have potential for application in DSSCs devices.

Effect of Position of Donor Units and Alkyl Groups on Dye-Sensitized Solar Cell Device Performance: Indoline-Aniline Donor-Based Visible Light Active Unsymmetrical Squaraine Dyes.

Indoline (In) and aniline (An) donor-based visible light active unsymmetrical squaraine (SQ) dyes were synthesized for dye-sensitized solar cells (DSSCs), where the position of An and In units was changed with respect to the anchoring group (carboxylic acid) to have In-SQ-An-CO2H and An-SQ-In-CO2H sensitizers, AS1-AS5. Linear or branched alkyl groups were functionalized with the N atom of either In or An units to control the aggregation of the dyes on TiO2. AS1-AS5 exhibit an isomeric π-framework where the squaric acid unit is placed in the middle, where AS2 and AS5 dyes possess the anchoring group connected with the An donor, and AS1, AS3, and AS4 dyes having the anchoring group connected with the In donor. Hence, the conjugation between the middle squaric acid acceptor unit and the anchoring -CO2H group is short for AS2, AS5, and AK2 and longer for AS1, AS3, and AS4 dyes. AS dyes showed absorption between 501 and 535 nm with extinction coefficients of 1.46-1.61 × 105 M-1 cm-1. Further, the isomeric π-framework of An-SQ-In-CO2H and In-SQ-An-CO2H exhibited by means of changing the position of In and An units a bathochromic shift in the absorption properties of AS2 and AS5 compared to the AS1, AS3, and AS4 dyes. The DSSC device fabricated with the dyes contains short acceptor-anchoring group distance (AS2 and AS5) showed high photovoltaic performances compared to the dyes having longer distance (AS1, AS3, and AS4) with the iodolyte (I-/I3-) electrolyte. DSSC device efficiencies of 5.49, 6.34, 6.16, and 5.57% have been achieved for AS1, AS2, AS3, and AS4 dyes, respectively; without chenodeoxycholic acid (CDCA), small changes have been observed in the device performance of the AS dyes with CDCA. Significant changes have been noted in the DSSC parameters (open-circuit voltage VOC, short-circuit current JSC, fill factor ff, and efficiency η) for the AS5 dye while sensitized with CDCA and showed highest DSSC efficiency of 8.01% in the AS dye series. This study revealed the potential of shorter SQ acceptor-anchoring group distance over the longer one and the importance of alkyl groups on the overall DSSC device performance for the unsymmetrical squaraine dyes.

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.

Efficient processed carbon Soot@MoS2 hybrid Bi-functional electrode for dye-sensitized solar cell and asymmetric supercapacitor devices

A feasible approach to rectify the world's energy demand using sustainable development of adequate energy generation and storage technologies in a single channel. In this respect, we made a holistic approach with a bi-functional electrode material to perform effectively in energy generation and storage applications. MoS2 nanosheets were produced by the eco-friendly method and reduced graphene oxide is used to prepared by carbon soot which is derived from castor oil. The prepared soot and rGO were combined with MoS2 nanosheets using a simple sonication method. The as-prepared sample was introduced in the supercapacitor and DSSC application. The combination MoS2@rGO provides an enhanced conversion efficiency of 11.81 ​% and the reproducibility of DSSC is also studied. Further, MoS2@rGO is used to fabricate an asymmetric supercapacitor to investigate its real-time application. The device produced the maximum power density (1666.6 ​mW/kg) and energy density (25.69 ​mWh/Kg) at 1 A/g. The asymmetric supercapacitor device holds a cyclic stability of 81.4 % for 5000 cycles and it powered up an LED device for 4 ​min.

The brief study of ZnO/PEDOT:PSS counter electrode in DSSC Based on solid electrolyte YSZ

Dye-Sensitized Solar Cell (DSSC) is a photovoltaic technology that is eco-friendly, has affordable costs, an easy fabrication process, and high power conversion efficiency. The application of solid electrolytes in DSSC is a promising option compared to using liquid electrolytes because liquid electrolytes easily cause corrosion on the photoanode and counter electrode. The role of the counter electrode in DSSC is crucial to speed up the electron transfer process to enhance the performance of DSSC devices. Much research on DSSC still uses a lot of platinum and graphene which are relatively expensive and supplies are limited. Therefore, this research will develop a low-cost and easy to fabricate counter electrode made of ZnO/PEDOT:PSS composite. Adding ZnO in PEDOT:PSS polymer can obtain higher catalytic activity, that can accelerate oxidation–reduction reactions to improve the performance of DSSC solar cells. From the results of this study, it can be concluded that the addition of ZnO mass to the ZnO/PEDOT: PSS composite can increase lattice parameters, crystal size, porosity values, and light absorbance. Based on the I-V testing, it shows that the addition of ZnO mass to the ZnO/PEDOT:PSS composite results in the highest efficiency of 3.29%.

Novel A-π-D-A organic dyes for better photovoltaic performance.

In this article, we report two indole-based metal-free organic dyes In-T-2C (3-(5-(3-((2-carboxy-2-cyanovinyl)-1-pentyl-1H-indol-5-yl)thiophen-2-yl)-2-isocyanoacrylic acid) and In-B-C (2-cyano-3-(5-(4-cyanophenyl)-1-pentyl-1H-indol-3-yl)acrylic acid) with A-π-D-A architecture. The molecular structures of metal-free indole-based A-π-D-A organic dyes were elucidated using FT-IR, NMR, HRMS and single-crystal X-ray diffraction techniques. The present investigation examined the features of the synthesized dyes employing photophysical attributes, electrochemical traits and theoretical studies were executed to acquire a detailed comprehension of the geometry, electronic structure and absorption spectra of the synthesized dyes using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Additionally, dye-sensitized solar cells (DSSCs) were fabricated using newly synthesized dyes and examined their photovoltaic activity. Electrochemical impedance analysis (EIS) was performed to recognize the interfacial charge transfer in the DSSCs. The In-T-2C dye-based DSSC device exhibited an uppermost fill factor (FF) of 0.63, resulting in the uppermost open-circuit voltage (V OC) of 540.2 mV and highest efficiency (η) of 4.12% due to the highest short-circuit current density (J SC) of 12.1 mA cm-2 compared to the In-B-C dye (V OC = 497 mV, J SC = 1.07, FF = 0.70, η = 0.38%).

Quantum Chemical Studies of Sensitizers Designed for Dye-Sensitive Solar Cells

In this study, two different organic dyes with a D-π1-R-π2-A structure were designed from the reference dye E0 with a D-π1-π2-A structure (E3-E4). By adding 2,3-dicyanopyrirazinophenanthrene between the π-bridges on the reference dye E0 and changing the π-bridge, dyes designed to examine the photovoltaic features for use in dye-sensitized solar cell (DSSC) devices were obtained. Various properties of the designed dyes, such as their geometrical structures, absorption spectra, nonlinear optical properties (NLOs), energy levels, boundary molecular orbitals, and some photovoltaic and chemical reactivity parameters, were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods to improve the performance of Dye-Sensitized Solar Cells (DSSCs). The calculated theoretical results concluded that E4 of the designed dyes can have a high short-circuit current and better power conversion energy (PCE) compared with E0. These results indicate that adding different auxiliary ligands and modifying the π-bridges can effectively improve the photovoltaic performance of the system.

Synthesis of ZnO-TiO2 Nanoparticles by Sol-Gel Process and its Application for Solar Cell Semiconductor

ZnO-TiO2 semiconductor can be used in Dye-Sensitized Solar Cell (DSSC) devices as an alternative to renewable energy. This semiconductor can be synthesized by sol-gel method. The objective of this study is synthesizing the TiO2-doped ZnO nanoparticle semiconductors for DSSC devices with mangosteen peel extract dye. Avocado seeds were extracted with water, as a capping agent in the synthesis of ZnO-TiO2 (TiO2 ratio of 0,3,5,7 and 10% to ZnO). XRD results show the success of ZnO-TiO2 doping, due to the 2θ shift and changes in the crystal lattice. The average crystal size obtained was 33.7972 nm. The SEM results showed that the particle size of ZnO ranged from 45-100 nm. The UV-Vis dye measurements of mangosteen peel extract showed an absorption peak at 296-483 nm wavelength, with a corresponding band gap energy value of 3.04 eV. The UV-Vis DRS ZnO-TiO2 measurements have an average band gap energy of 3.1425 eV and ZnOof 3.1915 eV. The highest DSSC efficiency value is 2.15 x 10-2% at 7% ZnO-TiO2 semiconductor.

NiSe2-CoSe2 hollow polyhedron as counter electrode catalyst for high-efficiency dye-sensitized solar cells

The design of efficient counter electrode (CE) materials for dye sensitized solar cells (DSSCs) strongly depend on the microstructure construction and the effective combination of different active components. In this study, a hollow polyhedral structured NiSe2-CoSe2 composite electrode was synthesized through the direct selenization of the hollow nanocage morphology nickel-cobalt layered double hydroxide (NiCo-LDH) ultrathin nanosheets, which was derived from ZIF-67 nanocrystals. Notably, owing to the unique hollow structure and synergistic effect of the Ni-Co bimetallic selenides, the hollow polyhedral NiSe2-CoSe2 CE exhibited the expected electrochemical catalytic activity in the reduction of triiodide, as revealed by electrochemical impedance spectroscopy, cyclic voltammetry and Tafel polarization measurements. The photovoltaic results revealed that the PCE of the NiSe2-CoSe2 CE reached 8.21 %, which was higher than those of the Pt and CoSe2 CEs (7.62 % and 6.78 %, respectively). Moreover, the hollow NiSe2-CoSe2 CE exhibited a favourable photocurrent response upon light on-and-off cycling and improved stability over multiple start. This study provides a meaningful reference for the construction of hollow polymetallic transition-metal selenides for DSSC devices.

Visible-Light-Active Unsymmetrical Squaraine Dyes with Pyridyl Anchoring Groups for Dye-Sensitized Solar Cells.

Visible-light-active alkyl group-wrapped unsymmetrical squaraine dyes SD1-SD3 were synthesized, featuring an indoline donor and pyridine and carboxylic acid anchoring groups. Their photophysical, electrochemical, and photovoltaic characteristics were examined by fabricating a dye-sensitized solar cell (DSSC) device. Both carboxylic acid and pyridine anchoring groups containing squaraine dyes SD3 and SD2 possess similar photophysical and electrochemical characteristics. However, their photovoltaic performances were completely different. The SD3 dye with the carboxylic acid anchoring group displayed a DSSC device efficiency of 7.20% (VOC 0.81 V; JSC 12.29 mA/cm2) using iodolyte (I-/I3-) electrolyte, compared to SD1 (VOC 0.659 V; JSC 4.97 mA/cm2; and η - 2.34%) and SD2 (VOC 0.629 V; JSC 1.68 mA/cm2; and η - 0.84%), which were featured with pyridyl anchoring groups. These results were attributed to dye loading on the Lewis and Brønsted acidic sites of TiO2 and the importance of aggregated structures for photocurrent generation. In the incident photon-to-current efficiency (IPCE) analysis, SD1 dye-sensitized devices exhibited photocurrent generation from both monomeric and aggregated dyes on the TiO2 surface. In contrast, SD2 showed photocurrent generation solely from aggregated states. Despite the introduction of long alkyl chains to reduce dye aggregation and charge recombination, the results indicated preferential charge injection from only the aggregated SD2 dye on TiO2. Fluorescence-quenching experiments indicated an efficient charge transfer from the aggregated SD2 dye to TiO2 compared to that of the monomeric dye. Cosensitization, a method to enhance the light-harvesting efficiency and photocurrent generation in DSSCs, was explored by simultaneously cosensitizing pyridyl-based dyes (SD1 and SD2) with a blue-colored carboxylic acid-based squaraine dye SD4. IPCE analysis demonstrated that both SD1 and SD4 contributed to generating a photocurrent of 9.11 mA/cm2. The sequential cosensitization of SD1 and SD4 with the coadsorbent CDCA showed the highest performance, with a VOC of 0.663 V, a JSC of 11.43 mA/cm2, and an efficiency (η) of 5.20%.