Porphyrin-sensitized solar cells with cobalt (II/III)-based redox electrolyte exceed 12 percent efficiency

Copper(ii) and cobalt(iii) Schiff base complexes with hydroxy anchors as sensitizers in dye-sensitized solar cells (DSSCs)

Two Schiff base complexes of copper(ii) and cobalt(iii) having the formulae [CuL₂] (Cu-Sal) and [CoL₃] (Co-Sal) (HL = 2-(((2-hydroxyethyl)imino)methyl)phenol) have been synthesized and characterized microanalytically, spectroscopically and in the case of Cu-Sal using single crystal X-ray diffraction technique. The single crystal X-ray analysis reveals a square planar geometry around Cu(ii) satisfied by phenoxide oxygen and imine nitrogen of the L^- ligand to generate a six membered chelate ring. The solid state structure of Cu-Sal is satisfied by varied intermolecular non-covalent interactions. The nature of these interactions has been addressed with the aid of Hirshfeld surface analysis. Both compounds have been used as sensitizers in TiO₂ based dye sensitized solar cells (DSSCs) and the DSSC experiments revealed that Co-Sal offers better photovoltaic performance in comparison to Cu-Sal. The Co-Sal exhibited a J _sc of 9.75 mA cm^-2 with a V _oc of -0.648 V, incident photon to current conversion efficiency (IPCE) of 57% and η of 3.84%. The relatively better photovoltaic performance of Co-Sal could be attributed to better light absorption and dye loading than that of Cu-Sal.

Protoporphyrin-sensitized degradable bismuth nanoformulations for enhanced sonodynamic oncotherapy

Decreasing the scavenging capacity of reactive oxygen species (ROS) and enhancing ROS production are the two principal objectives in the development of novel sonosensitizers for sonodynamic therapy (SDT). Herein, we designed a protoporphyrin-sensitized bismuth-based semiconductor (P-NBOF) as a sonosensitizer to generate ROS and synergistically depleted glutathione for enhanced SDT against tumors. The bismuth-based nanomaterial (NBOF) is a wide-bandgap semiconductor. Sensitization by protoporphyrin made it easier to excite electrons under ultrasonic stimulation, and the energy of the lowest unoccupied electron orbital in protoporphyrin was higher than the conduction-band energy of NBOF. Under ultrasound excitation, the excited electrons in the protoporphyrin were injected into the conduction band of the NBOF, increasing its reducing ability leading to the production of more superoxide anion radicals and also helping to increase the charge separation of protoporphyrin leading to the production of more singlet oxygen. Meanwhile, P-NBOF continuously depleted glutathione, which was not only conducive to breaking the redox balance of the tumor microenvironment to enhance the therapeutic efficacy of SDT, but also promoted its degradation and metabolism. The construction of this P-NBOF sonosensitizer thus provided an effective strategy to enhance SDT for tumors. STATEMENT OF SIGNIFICANCE: To enhance the efficacy of sonodynamic tumor therapy, we developed a degradable protoporphyrin-sensitized bismuth-based nano-semiconductor (P-NBOF) by optimizing the band structure and glutathione-depletion ability. Protoporphyrin in P-NBOF under excitation preferentially generates free electrons, which are then injected into the conduction band of NBOF, improving the reducing ability of NBOF and promoting the separation of electron-hole pairs, thereby enhancing the production capacity of reactive oxygen species. Furthermore, P-NBOF can deplete glutathione, reduce the scavenging of reactive oxygen species, and reactivate and amplify the effect of sonodynamic therapy. The construction of the nanotherapeutic platform provides an option for enhancing sonodynamic therapy.

Preparation and Photovoltaic Evaluation of CuO@Zn(Al)O-Mixed Metal Oxides for Dye Sensitized Solar Cell

In this manuscript, a series of dye-sensitized solar cells (DSSCs) were fabricated as a function of post-processing temperature based on mesoporous CuO@Zn(Al)O-mixed metal oxides (MMO) in conjunction with dye N719 as the main light absorber; the proposed CuO@Zn(Al)O geometry was, in turn, attained using Zn/Al-layered double hydroxide (LDH) as a precursor via combination of co-precipitation and hydrothermal techniques. In particular, the dye loading amount onto the deposited mesoporous materials was anticipated via regression equation-based UV-Vis technique analysis, which evidently demonstrated a robust correlation along with the fabricated DSSCs power conversion efficiency. In detail, of the DSSCs assembled, CuO@MMO-550 exhibited short-circuit current (JSC) and open-circuit voltage (VOC) of 3.42 (mA/cm²) and 0.67 (V) which result in significant fill factor and power conversion efficiency of 0.55% and 1.24%, respectively. This could mainly be due to the relatively high surface area of 51.27 (m²/g) which in turn validates considerable dye loading amount of 0.246 (mM/cm^-2).

Redox Shuttle-Based Electrolytes for Dye-Sensitized Solar Cells: Comprehensive Guidance, Recent Progress, and Future Perspective

A redox electrolyte is a crucial part of dye-sensitized solar cells (DSSCs), which plays a significant role in the photovoltage and photocurrent of the DSSCs through efficient dye regeneration and minimization of charge recombination. An I^-/I₃ ^- redox shuttle has been mostly utilized, but it limits the open-circuit voltage (V _oc) to 0.7-0.8 V. To improve the V _oc value, an alternative redox shuttle with more positive redox potential is required. Thus, by utilizing cobalt complexes with polypyridyl ligands, a significant power conversion efficiency (PCE) of above 14% with a high V _oc of up to 1 V under 1-sun illumination was achieved. Recently, the V _oc of a DSSC has exceeded 1 V with a PCE of around 15% by using Cu-complex-based redox shuttles. The PCE of over 34% in DSSCs under ambient light by using these Cu-complex-based redox shuttles also proves the potential for the commercialization of DSSCs in indoor applications. However, most of the developed highly efficient porphyrin and organic dyes cannot be used for the Cu-complex-based redox shuttles due to their higher positive redox potentials. Therefore, the replacement of suitable ligands in Cu complexes or an alternative redox shuttle with a redox potential of 0.45-0.65 V has been required to utilize the highly efficient porphyrin and organic dyes. As a consequence, for the first time, the proposed strategy for a PCE enhancement of over 16% in DSSCs with a suitable redox shuttle is made by finding a superior counter electrode to enhance the fill factor and a suitable near-infrared (NIR)-absorbing dye for cosensitization with the existing dyes to further broaden the light absorption and enhance the short-circuit current density (J _sc) value. This review comprehensively analyzes the redox shuttles and redox-shuttle-based liquid electrolytes for DSSCs and gives recent progress and perspectives.

Scanning Electrochemical Microscope Studies of Charge Transfer Kinetics at the Interface of the Perovskite/Hole Transport Layer

Interfacial carrier transfer kinetics is critical to the efficiency and stability of perovskite solar cells. Herein, we measure the regeneration rate constant, absorption cross-section, reduction rate constant, and conductivity of hole transport layered perovskites using scanning electrochemical microscopy (SECM). The SECM feedback revealed that the regeneration rate constant, absorption cross-section, and reduction rate constant of the nickel oxide (NiO) layer perovskite layer are higher than those of the poly (3,4-ethyenedioxythiophene)-poly (styrenesulfonate) layered perovskite. Also, at a specific flux density ( $J_{hv}$ ), the value of the regeneration rate constant (keff) in both blue and red illuminations for the NiO/CH3NH3PbI3 film is significantly higher than in both PEDOT: PSS/CH3NH3PbI3 and FTO/CH3NH3PbI3 films. The difference in keff between layered and nonlayered perovskite conforms to the impact of the hole conducting layer on the charge transfer kinetics. According to the findings, SECM is a powerful approach for screening an appropriate hole transport layer for stable perovskite solar cells.

A Molecularly Tailored Photosensitizer with an Efficiency of 13.2% for Dye-Sensitized Solar Cells

Photosensitizers yielding superior photocurrents are crucial for copper-electrolyte-based highly efficient dye-sensitized solar cells (DSCs). Herein, two molecularly tailored organic sensitizers are presented, coded ZS4 and ZS5, through judiciously employing dithieno[3,2-b:2″,3″-d]pyrrole (DTP) as the π-linker and hexyloxy-substituted diphenylquinoxaline (HPQ) or naphthalene-fused-quinoxaline (NFQ) as the auxiliary electron-accepting unit, respectively. Endowed with the HPQ acceptor, ZS4 shows more efficient electron injection and charge collection based on substantially reduced interfacial charge recombination as compared to ZS5. As a result, ZS4-based DSCs achieve a power conversion efficiency (PCE) of 13.2% under standard AM1.5G sunlight, with a high short-circuit photocurrent density (J_sc ) of 16.3 mA cm^-2 , an open-circuit voltage (V_oc ) of 1.05 V and a fill factor (FF) of 77.1%. Remarkably, DSCs sensitized with ZS4 exhibit an outstanding stability, retaining 95% of their initial PCE under continuous light soaking for 1000 h. It is believed that this is a new record efficiency reported so far for copper-electrolyte-based DSCs using a single sensitizer. The work highlights the importance of developing molecularly tailored photosensitizers for highly efficient DSCs with copper electrolyte.

Biomimicry in nanotechnology: a comprehensive review

Biomimicry has been utilized in many branches of science and engineering to develop devices for enhanced and better performance. The application of nanotechnology has made life easier in modern times. It has offered a way to manipulate matter and systems at the atomic level. As a result, the miniaturization of numerous devices has been possible. Of late, the integration of biomimicry with nanotechnology has shown promising results in the fields of medicine, robotics, sensors, photonics, etc. Biomimicry in nanotechnology has provided eco-friendly and green solutions to the energy problem and in textiles. This is a new research area that needs to be explored more thoroughly. This review illustrates the progress and innovations made in the field of nanotechnology with the integration of biomimicry.

Effect of regio-specific arylamine substitution on novel π-extended zinc salophen complexes: density functional and time-dependent density functional study on DSSC applications

A series of π-extended salophen-type Schiff-base zinc(ii) complexes, e.g., zinc-salophen complexes (ZSC), were investigated toward potential applications for dye-sensitized solar cells. The ZSC dyes adopt linear-, X-, or π-shaped geometries either with the functionalization of 1 donor/1 acceptor or 2 donors/2 acceptors to achieve a push-pull type molecular structure. The frontier molecular orbitals, light-harvesting properties as well as charge transfer characters against regio-specific substitution of donor/acceptor groups were studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results reveal that all ZSC dyes of D-ZnS-π-A geometry (where D, S, and A denote to donor, salophen ligand, and acceptor, respectively) exhibit relatively lower HOMO energy compared to the structurally resembled porphyrin dye YD2-o-C8. Natural transition orbital (NTO) and electron-hole separation (EHS) approaches clearly differentiate the linear type YD-series dyes from CL-, AJ1-, and AJ2-series dyes because of poor charge transfer (CT) properties. In contrast, the π-shaped AJ2-series and X-shaped AJ1-series dyes outperform the others in a manner of stronger CT characteristics, broadened UV-vis absorption as well as tunable bandgap simply via substitution of p-ethynylbenzoic acids (EBAs) and arylamine donors at salophen 7,8- and 2,3,12,13-positions, respectively. Both EHS and calculated exciton binding energies suggest the strength of CT character for ZSC dyes with an amino donor in the trend TPA > AN > DPA. This work has provided clear illustration toward molecular design of efficient dyes featuring a zinc-salophen backbone.

Photoelectrochemical approaches for the conversion of lignin at room temperature

The selective cleavage of C-C/C-O linkages represents a key step toward achieving the chemical conversion of biomass to targeted value-added chemical products under ambient conditions. Using photoelectrosynthetic solar cells is a promising method to address the energy intensive depolymerization of lignin for the production of biofuels and valuable chemicals. This feature article gives an in-depth overview of recent progress using dye-sensitized photoelectrosynthetic solar cells (DSPECs) to initiate the cleavage of C-C/C-O bonds in lignin and related model compounds. This approach takes advantage of N-oxyl mediated catalysis in organic electrolytes and presents a promising direction for the sustainable production of chemicals currently derived from fossil fuels.

Electronic, geometrical and photophysical facets of five coordinated porphyrin N-heterocyclic carbene transition metals complexes: A theoretical study

In the realm of dye sensitized solar cells (DSSCs), the 3d transition metals as photosensitizers are scarcely studied. In the present work, electronic structures, FMO, MEP surfaces, NBO analysis, energetics and photophysical properties of earth abundant metals (Mn, Fe and Co) based metalloporphyrins coordinated with NHC-carbene have been explored by using DFT and TDDFT calculations. According to formation energies and energy decomposition analysis (EDA), the cobalt based metalloporphyrins species are found to be more stable while in contrast manganese based species are predicted as more reactive among all. Also, from the ligation point of view, the TPP (meso-tetraphenylporphyrin) ligand forms more steady and rigid coordination as compare to the TTP (meso-tetratolylporphyrin) ligand. FMO analysis also support these observations. NBO and SNO results support the electronic configurations as well as unveil the controversial bonding pattern of NHC_carbon and metal atom and found that there is σ-bonding present between the metal and the NHC_carbon by the overlapping of sp-hybridized orbitals of carbene_carbon and sp/d hybrid orbital of the metal atom. TDDFT results show that the highest light harvesting efficiency (LHE) of all the studied species is found under the range of 360 nm - 380 nm (λ) and this may due to the presence of longer π-conjugations. In-depth investigation of this work may help to design new robust energy harvesting systems for high energy conversion efficiency based on earth abundance metals. Our results are in well agreement with the available experimental findings.

Computational study of linear carbon chain based organic dyes for dye sensitized solar cells

Spectroscopic, electronic and electron injection properties of a new class of linear carbon chain (LCC) based organic dyes have been investigated, by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT), for application in dye-sensitized solar cells (DSSCs). The photophysical properties of LCC-based dyes are tuned by changing the length of the linear carbon chain; UV/VIS absorption is red-shifted with increasing LCC length whereas oscillator strength and electron injection properties are reduced. Excellent nonlinear optical properties are predicted in particular for PY-N4 and PY-S4 dyes in the planar conformation. Results indicate that a LCC-bridge produces better results compared to benzene and thiophene bridges. Simulations of I--Dye@(TiO2)14 and Dye@(TiO2)14 anatase complexes indicate that designed dyes inject electrons efficiently into the TiO2 surface and can be regenerated by electron transfer from the electrolyte. Superior properties in terms of efficiency are shown by compounds with a pyrrole ring as the donor group and PY-3N is expected to be a promising candidate for applications, however all the investigated dyes could provide a good performance in solar energy conversion. Our study demonstrates that computational design can provide a significant contribution to experimental work; we expect this study will contribute to future developments to identify new and highly efficient sensitizers.

Hydroxamic acid pre-adsorption raises the efficiency of cosensitized solar cells

Dye-sensitized solar cells (DSCs) convert light into electricity by using photosensitizers adsorbed on the surface of nanocrystalline mesoporous titanium dioxide (TiO₂) films along with electrolytes or solid charge-transport materials^1-3. They possess many features including transparency, multicolour and low-cost fabrication, and are being deployed in glass facades, skylights and greenhouses⁴. Recent development of sensitizers^5-10, redox mediators^11-13 and device structures¹⁴ has improved the performance of DSCs, particularly under ambient light conditions^14-17. To further enhance their efficiency, it is pivotal to control the assembly of dye molecules on the surface of TiO₂ to favour charge generation. Here we report a route of pre-adsorbing a monolayer of a hydroxamic acid derivative on the surface of TiO₂ to improve the dye molecular packing and photovoltaic performance of two newly designed co-adsorbed sensitizers that harvest light quantitatively across the entire visible domain. The best performing cosensitized solar cells exhibited a power conversion efficiency of 15.2% (which has been independently confirmed) under a standard air mass of 1.5 global simulated sunlight, and showed long-term operational stability (500 h). Devices with a larger active area of 2.8 cm² exhibited a power conversion efficiency of 28.4% to 30.2% over a wide range of ambient light intensities, along with high stability. Our findings pave the way for facile access to high-performance DSCs and offer promising prospects for applications as power supplies and battery replacements for low-power electronic devices^18-20 that use ambient light as their energy source.

Influence of Redox Couple on the Performance of ZnO Dye Solar Cells and Minimodules with Benzothiadiazole-Based Photosensitizers

ZnO-based dye-sensitized solar cells exhibit lower efficiencies than TiO2-based systems despite advantageous charge transport dynamics and versatility in terms of synthesis methods, which can be primarily ascribed to compatibility issues of ZnO with the dyes and the redox couples originally optimized for TiO2. We evaluate the performance of solar cells based on ZnO nanomaterial prepared by microwave-assisted solvothermal synthesis, using three fully organic benzothiadiazole-based dyes YKP-88, YKP-137, and MG-207, and alternative electrolyte solutions with the I-/I3 -, Co(bpy)3 2+/3+, and Cu(dmp)2 1+/2+ redox couples. The best cell performance is achieved for the dye-redox couple combination YKP-88 and Co(bpy)3 2+/3+, reaching an average efficiency of 4.7% and 5.0% for the best cell, compared to 3.7% and 3.9% for the I-/I3 - couple with the same dye. Electrical impedance spectroscopy highlights the influence of dye and redox couple chemistry on the balance of recombination and regeneration kinetics. Combined with the effects of the interaction of the redox couple with the ZnO surface, these aspects are shown to determine the solar cell performance. Minimodules based on the best systems in both parallel and series configurations reach 1.5% efficiency for an area of 23.8 cm2.

Electrodeposited PPy@TiO2 and PEDOT@TiO2 Counter Electrodes for [Co(bpy)3]2+/3+ Redox Mediator-Based Dye-Sensitized Solar Cells

The main goal of this work is to enhance the catalytic performance of PPy and PEDOT films toward the Co2+/Co3+ redox couple. PPy and PEDOT films were electrodeposited separately on a porous TiO2 template to assess their suitability as alternative catalysts in dye-sensitized solar cells (DSSC) based on the [Co(bpy)3]2+/3+ redox shuttle. The obtained PPy@TiO2 and PEDOT@TiO2 counter electrodes displayed much rougher surfaces. Electrochemical studies indicate the superior catalytic activity of both the electrodeposited electrodes toward Co3+ reduction, as indicated by lower charge transfer resistance than that of pristine films and even that of Pt electrodes. Therefore, the fabricated DSSC devices with these counter electrodes achieved higher power conversion efficiencies compared to cells with pristine PPy and PEDOT counter electrodes, or even with a Pt counter electrode. Interestingly, the assembled DSSC device with a PEDOT@TiO2 counter electrode displayed the highest performance among all with a power conversion efficiency of 6.62%, which is better than that obtained by the device with a Pt electrode (6.07%).

Naphthoquinoneoxime-Sensitized Titanium Dioxide Photoanodes: Photoelectrochemical Properties

Naphthoquinoneoxime derivatives, viz., LwOx, 3-hydroxy-4-(hydroxyimino)naphthalen-1 (4H)-one; PthOx, 3-hydroxy-4-(hydroxyimino)-2-methylnaphthalen-1(4H)-one; and Cl_LwOx, 2-chloro-3-hydroxy-4-(hydroxyimino)naphthalen-1(4H)-one, are used in fabrication of dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the sensitizers were studied. The HOMO-LUMO energy gaps of the sensitizers (LwOx, PthOx, and Cl_LwOx) calculated by using the intersection of UV-visible and fluorescence spectra are 2.85, 2.71, and 2.87 eV, respectively. The energy band alignment energy level of the sensitizer, that is, the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), should match with the energy level of the TiO₂ conduction band and the redox potential of iodine/triiodide electrolyte to allow smooth electron transfer. The electrochemical characterization of sensitizers was done to find the LUMO and HOMO level of the sensitizer. It shows that the LUMO level of (LwOx, PthOx, and Cl_LwOx) is above the conduction band position of TiO₂. Electrochemical impedance spectroscopy was used to study the charge transport resistance and electron lifetime of DSSCs. The charge transport resistance at the TiO₂ |electrolyte|counter electrode interface was reduced in the Cl_LwOx device; thus, the electron lifetime of Cl_LwOx was enhanced compared to LwOx and PthOx sensitizers. The fabricated device was characterized using photocurrent density-voltage (J-V) measurement. It is observed that there was an enhancement in the overall power conversion efficiency (η) of the DSSCs fabricated by using Cl_LwOx sensitizers as compared to LwOx and PthOx sensitizer-loaded photoanodes. Enhancement in power conversion efficiency, that is, photovoltage and photocurrent, is achieved due to the chlorine substituent. Thus, the chlorine substituent naphthoquinoneoxime pushes the electron density, enhancing the pushing nature and facilitating the lone pair present in the N-OH moiety to attach to TiO₂ more strongly.

The effects of copper doping on morphology and room-temperature photoluminescence of ZnO nanocolumns

In this study, a versatile vapor phase transport method for the synthesis and copper-doping of ZnO nanocolumns is demonstrated. Doping percentage (up to 5%) showed no effect on the wurtzite structural phase of ZnO nanocolumns. However, a decrease in nanocolumn diameter (cross-sectional length of longest side or diagonal) due to doping was observed by scanning electron microscopy. Reduced rate of electron-hole recombination was inferred from a decrease in the intensity of the near-band edge emission peak shown in room-temperature photoluminescence spectra. Expression of structural defects in both doped and undoped nanocolumns suggest p-type conductivity. Observed copper-doping effects show promise for utilizing such structures as electrode components in dye-sensitized solar cells.

Computational investigation on the geometry and electronic structures and absorption spectra of metal-porphyrin-oligo- phenyleneethynylenes-[60] fullerene triads

In this work, we focus our attention on the influence of 2nd-row transition metals on the structural geometries, electronic structures, and absorption characteristics of porphyrin linked with the C₆₀ fullerene with oligo-p-phenyleneethynylenes (MP-C₆₀-oligo-PPEs) compounds. The DFT/B3PW91-D3 and CAM-B3LYP-D3/6-31G (d) calculations revealed that various metals embedded within the porphyrin moiety give different bridge conformations and different HOMO-LUMO energy levels. We calculate the UV-Vis spectra and absorption parameters using the time-dependent ZINDO/S approach. Our findings indicate that all the compounds have enhanced absorptions in the visible light range, and their molecular orbital energies adopt the condition of sensitizers. However, all of the complexes except down spin states exhibit considerably charge spatial separation. The results suggest that the ZnP-C₆₀-oligo-PPEs triad can meet the necessary conditions of the sensitizer of dye-sensitized solar cells (DSSCs) in comparison with other counterparts and could be an optimum triad compound for potential application in photovoltaic devices.

A double co-sensitization strategy using heteroleptic transition metal ferrocenyl dithiocarbamate phenanthrolene-dione for enhancing the performance of N719-based DSSCs

Three new heteroleptic dithiocarbamate complexes with formula [M(Phen-dione)(Fcdtc)]PF6 (where M = Ni(ii) Ni-Fc, Cu(ii) Cu-Fc) and [Co(Phen-dione)(Fcdtc)2]PF6 (Co-Fc) (Fcdtc = N-ethanol-N-methylferrocene dithiocarbamate and Phen-dione = 1,10-phenanthroline-5,6-dione; PF6 - = hexafluorophosphate) were synthesized and characterized using microanalysis, FTIR, electronic absorption spectroscopy and mass spectrometry. The solution state electronic absorption spectroscopy for all three complexes displayed a band at ∼430 nm corresponding to the ferrocene unit and another low-intensity band in the visible region arising because of the d-d transitions. These newly synthesized complexes were used as co-sensitizers for the state-of-the-art di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(ii) (N719) dye in dye-sensitized solar cells (DSSCs). Among the three co-sensitizers/co-adsorbent-based DSSC set-ups, the assembly fabricated using Co-Fc/N719 displayed good photovoltaic performance with 5.31% efficiency (η) while a new triple component strategy inculcating N719, Co-Fc and Cu-Fc dyes offered the best photovoltaic performance with 6.05% efficiency (η) with incident photon to current conversion efficiency (IPCE) of 63%. This indicated an upliftment of the DSSC performance by ∼38% in comparison to the set-up constructed by employing only N719 dye (η = 4.39%) under similar experimental conditions.

Biomedical Photoacoustic Imaging for Molecular Detection and Disease Diagnosis: "Always-On" and "Turn-On" Probes

Photoacoustic (PA) imaging is a nonionizing, noninvasive imaging technique that combines optical and ultrasonic imaging modalities to provide images with excellent contrast, spatial resolution, and penetration depth. Exogenous PA contrast agents are created to increase the sensitivity and specificity of PA imaging and to offer diagnostic information for illnesses. The existing PA contrast agents are categorized into two groups in this review: "always-on" and "turn-on," based on their ability to be triggered by target molecules. The present state of these probes, their merits and limitations, and their future development, is explored.

Modification of DSSC Based on Polymer Composite Gel Electrolyte with Copper Oxide Nanochain by Shape Effect

Solvent evaporation and leakage of liquid electrolytes that restrict the practicality of dye-sensitized solar cells (DSSCs) motivate the quest for the development of stable and ionic conductive electrolyte. Gel polymer electrolyte (GPE) fits the criteria, but it still suffers from low efficiency due to insufficient segmental motion within the electrolytes. Therefore, incorporating metal oxide nanofiller is one of the approaches to enhance the performance of electrolytes due to the presence of cross-linking centers that can be coordinated with the polymer segments. In this research, polymer composite gel electrolytes (PCGEs) employing poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (P(VB-co-VA-co-VAc)) terpolymer as host polymer, tetrapropylammonium iodide (TPAI) as dopant salt, and copper oxide (CuO) nanoparticles as the nanofillers were produced. The CuO nanofillers were synthesized by sonochemical method and subsequently calcined at different temperatures (i.e., 200, 350, and 500 °C), denoted as CuO-200, CuO-350, and CuO-500, respectively. All CuO nanoparticles have different shapes and sizes that are connected in a chain which impact the amorphous phase and the roughness of the surface, proven by the structural and the morphological analyses. It was found that the PCGE consisting of CuO-350 exhibited the highest ionic conductivity of 2.54 mS cm⁻¹ and apparent diffusion coefficient of triiodide of 1.537 × 10⁻⁴ cm² s⁻¹. The enhancement in the electrochemical performance of the PCGEs is correlated with the change in shape (rod to sphere) and size of CuO particles which disrupted the structural order of the polymer chain, facilitating the redox couple transportation. Additionally, a DSSC was fabricated and achieved the highest power conversion efficiency of 7.05% with J_SC of 22.1 mA cm⁻², V_OC of 0.61 V, and FF of 52.4%.

Efficient Solar Cells Sensitized by Organic Concerted Companion Dyes Suitable for Indoor Lamps

In this work, organic concerted companion (CC) dyes CCOD-1 and CCOD-2 were constructed by covalently linking two organic dye units with complementary absorption spectra. Both CC dyes exhibited intense absorption from 300 to 650 nm with the band edges extended to 700 nm. These CC dyes were used to fabricate dye-sensitized solar cells (DSSCs), and the photovoltaic performance was investigated using different light sources. CCOD-2 possessed bulkier outer shelter than CCOD-1 owing to the longer carbon chains (C₁₂ ) at the donor moiety, and thus it had stronger anti-aggregation and anti-charge-recombination ability. Under simulated sunlight (AM1.5G), CCOD-2 exhibited enhanced photovoltaic behavior with an open-circuit voltage (V_OC ) of 759 mV, short-circuit current density (J_SC ) of 19.23 mA ⋅ cm^-2 , and power conversion efficiency (PCE) of 10.4 %, respectively. Notably, under the illumination of the indoor T5 fluorescent lamp (2500 lux), CCOD-2 afforded an enhanced PCE of 28.0 % with remarkable V_OC and J_SC of 692 mV and 0.424 mA cm^-2 , respectively. Notably, the PCE achieved for CCOD-2 outperformed those of the reference sensitizer N719 and our previously reported CC dyes XW61 and XW70-C8 under the same indoor lamp conditions. In summary, the novel organic CC dyes developed in this work were demonstrated to be promising for fabricating DSSCs to efficiently harvest the energy of indoor lamps.

A comparative study of the mechanical stability, electronic, optical and photocatalytic properties of CsPbX3 (X = Cl, Br, I) by DFT calculations for optoelectronic applications

Organic free Cs-based perovskite materials are potential candidates for electronic and optoelectronic applications. A systematic comparative study of the mechanical, electronic, optical, and photocatalytic properties of CsPbX3 (X = Cl, Br, I) was conducted using density functional theory to compare the applicability of these materials in optoelectronic, photocatalytic, and photovoltaic (PV) devices. We calculated structural and elastic properties to determine the better agreement of damage-tolerance and electronic and optical responses for suitable device applications. Optimized lattice parameters and elastic constants showed excellent agreement with the experimental data whereas some properties were found to be much better than other theoretical reports. CsPbBr3 is thermodynamically more stable and more ductile compared to the other two perovskites. The hydrostatic pressure dependent mechanical stability showed that CsPbCl3 and CsPbBr3 sustained stability under low applied pressure, whereas the stability of CsPbI3 was very high. The electronic band gap calculations showed that CsPbCl3, CsPbBr3, and CsPbI3 are suitable for green, orange, and red emissions of optical spectra owing to the proper electronic band gaps. CsPbI3 can be shown as the best photocatalyst for the hydrogen evolution reaction and CsPbBr3 is the most stable photocatalyst due to its nearly balanced oxidation and reduction potentials, but CaPbCl3 is better for O2 production. The density of states and other optical properties have been reported in this study. Thus, our findings would be beneficial for experimental studies and can open a new window for efficient electronic, optoelectronic, and hydrogen production along with the biodegradation of polluted and waste materials.

Efficient Dye-Sensitized Solar Cells Based on a New Class of Doubly Concerted Companion Dyes

To develop efficient dye-sensitized solar cells (DSSCs), concerted companion (CC) dyes XW60-XW63 constructed from the covalent linkage of a strapped porphyrin dye unit and an organic dye unit have been reported to exhibit panchromatic absorption and excellent photovoltaic performance. However, these CC dyes only afforded moderate VOC values of ca. 763 mV, demonstrating relatively weak antiaggregation ability, which remains an obstacle for further enhancing the photovoltaic behavior. To address this problem, we herein develop porphyrin dyes XW77-XW80 with the macrocycles wrapped with alkoxy chains of various lengths (OC6H13-OC22H45) and the corresponding CC dyes XW81-XW84 containing these porphyrin dye units. Interestingly, the new CC dyes XW81-XW83 exhibit increasing VOC from 745 to 784 mV with the chain lengths extended from C6 to C18, and a lowered VOC of 762 mV was obtained for XW84 when the chain length was further extended to C22. As a result, XW83 afforded the highest PCE of 12.2%, which is, to the best of our knowledge, the record efficiency for the iodine electrolyte-based solar cells sensitized with a single dye. These results can be rationalized by the so-called doubly concerted companion (DCC) effects, that is, the two subdye units exhibit not only complementary absorption but also concerted antiaggregation with the long wrapping chains on the porphyrins unit simultaneously protecting the porphyrin macrocycle and the neighboring organic subdye unit, thus affording panchromatic absorption and strong antiaggregation and anticharge-recombination ability. These results provide a new approach for constructing a class of DCC dyes to achieve high-performance DSSCs without using any antiaggregating coadsorbent or absorption-enhancing cosensitizer.

Improvements in photoelectric performance of dye-sensitised solar cells using ionic liquid-modified TiO2 electrodes

One of the major problems in dye-sensitised solar cells (DSSCs) is the aggregation of dyes on TiO₂ electrodes, which leads to undesirable electron transfer. Various anti-aggregation agents, such as deoxycholic acid, have been proposed and applied to prevent dye aggregation on the electrodes. In this study, we designed and synthesised a phosphonium-type ionic liquid that can be modified on the TiO₂ electrode surface and used as a new anti-aggregation agent. Although the modification of the ionic liquid onto the electrode reduced the amount of dye adsorbed on the electrode, it showed a significant anti-aggregation effect, thereby improving the photovoltaic performance of DSSCs with N3 and J13 dyes. This finding suggests that ionic liquids are effective as anti-aggregation agents for DSSCs.

The modification of the phosphonium-type ionic liquid onto the TiO₂ electrode reduced the amount of dye adsorbed on the electrode and showed significant aggregation effect, thereby improving the photovoltaic performance of DSSCs.

NIR-II J-Aggregated Pt(II)-Porphyrin-Based Phosphorescent Probe for Tumor-Hypoxia Imaging

The luminescence of traditional phosphorescence-based hypoxia probes is limited to the visible and first near-infrared wavelength regions (<1000 nm), which has defects of higher light scattering and lower penetration depth in contrast with the second near-infrared wavelength window (NIR-II, 1000-1700 nm) for optical bioimaging. Herein, 5,15-bis(2,6-bis(dodecyloxy)phenyl)-porphyrin platinum(II) (PpyPt) with J-aggregation induced NIR-II phosphorescence is reported. J-aggregates of PpyPt are confirmed by the X-ray diffraction data in the crystalline state. Moreover, the emission and excitation spectra of PpyPt in the solid states reveal NIR-II luminescence feature of PpyPt in J-aggregates. More importantly, by preparation of water-soluble PpyPt nanoparticles (PpyPt NPs_4.76 ) with J-aggregates, it has NIR-II phosphorescent lifetime of microseconds and good oxygen-sensitivity in water. Moreover, the good biological hypoxia-sensing potential of PpyPt NPs_4.76 is demonstrated in cells and 4T1-tumor-bearing mice. This study provides an efficient strategy to design NIR-II phosphorescent probe for sensitive tumor-hypoxia detection through the construction of J-aggregates.

Conformation-related excited-state charge transfer/separation of donor-π-acceptor chromophores

Understanding the excited-state charge transfer/separation (CT/CS) of donor-π-acceptor chromophores can provide guidance for designing and synthesizing advanced dyes to improve the performance of dye-sensitized solar cells (DSSCs) in practical applications. Herein, two newly synthesized electronic push-pull molecules, CS-14 and CS-15, that consist of carbazole donor and benzothiadiazole acceptor segments are chosen to explore the ultrafast dynamics of intramolecular CT/CS processes. The theoretical calculation results depict an excited-state intramolecular CT character for both dyes, while the dihedral angle between donor and acceptor of CS-14 is larger than that of CS-15, suggesting a more significant CT character of CS-14. Furthermore, compared to CS-14, the bond rotation of CS-15 between donor and π-bridge is restricted by employing the hexatomic ring, indicating the stronger molecular planarization of CS-15. Ultrafast spectroscopy clearly shows a solvent polarity-dependent excited-state species evolution from CT to CS-the CT character is observed in low-polar toluene solvent, while the feature of the CS state in polar tetrahydrofuran and acetone solvents is captured, which successfully proved a solvent polarity modulated excited-state CT/CS characters. We also found that though the generation of the CS state within CS-14 is slightly faster than that of CS-15, the charge recombination process of CS-15 with excellent planar conformation is much slower, providing enough time for a higher charge migration efficiency in DSSCs.

Ionic liquid dispersed highly conducting polymer electrolyte for supercapacitor application: Current scenario and prospects “ICSEM 2021”

Ionic liquid (IL) is now being considered as a novel contender in the development of highly conducting polymer electrolytes rather than a solvent. It has a significant impact on the electrochemical performance of polymer electrolytes. This study emphasizes the significance of low viscosity IL dispersion within a polymer (PVA) matrix. The electrical, structural and photoelectrochemical properties of the IL-doped polymer electrolyte are discussed in detail. These highly conducting IL doped solid polymer electrolytes show promise towards the development of highly efficient Supercapacitors.

Synthesis, Characterization, and Studies on Photophysical Properties of Rhodamine Derivatives and Metal Complexes in Dye-Sensitized Solar Cells

Rhodamine 6G dyes are low-cost, highly soluble fluorescent dyes frequently utilized as laser dyes, chemical sensors, and as tracer dyes in the determination of the direction and rate of flow of water. In this study, the photophysical properties of three rhodamine 6G dyes, bearing phenyl (P15), furan (P41), and 5-hydroxymethyl furan (P45), and their metal complexes were investigated using ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy, fluorescence lifetime, and Fourier transform infrared (FTIR) measurements. Rhodamine 6G dyes and their complexes were subsequently applied as sensitizing dyes in the fabrication of dye-sensitized solar cells, and the solar to electric power efficiency and electrochemical impedance spectroscopy measurements were performed. The solar to electric power efficiency values of the metal complexes of the rhodamine 6G dyes were higher than those of the devices fabricated with only rhodamine dyes without copper (II). The most significant change was observed in rhodamine P41 with a 30% increase in solar to electric power efficiency when the dye was conjugated to the copper ion.

Electrical Transport, Structural, Optical and Thermal Properties of [(1-x)Succinonitrile: xPEO]-LiTFSI-Co(bpy)3(TFSI)2-Co(bpy)3(TFSI)3 Solid Redox Mediators

The solar cell has been considered one of the safest modes for electricity generation. In a dye-sensitized solar cell, a commonly used iodide/triiodide redox mediator inhibits back-electron transfer reactions, regenerates dyes, and reduces triiodide into iodide. The use of iodide/triiodide redox, however, imposes several problems and hence needs to be replaced by alternative redox. This paper reports the first Co2+/Co3+ solid redox mediators, prepared using [(1−x)succinonitrile: xPEO] as a matrix and LiTFSI, Co(bpy)3(TFSI)2, and Co(bpy)3(TFSI)3 as sources of ions. The electrolytes are referred to as SN_E (x = 0), Blend 1_E (x = 0.5 with the ethereal oxygen of the PEO-to-lithium ion molar ratio (EO/Li+) of 113), Blend 2_E (x = 0.5; EO/Li+ = 226), and PEO_E (x = 1; EO/Li+ = 226), which achieved electrical conductivity of 2.1 × 10−3, 4.3 × 10−4, 7.2 × 10−4, and 9.7 × 10−7 S cm−1, respectively at 25 °C. Only the blend-based polymer electrolytes exhibited the Vogel-Tamman-Fulcher-type behavior (vitreous nature) with a required low pseudo-activation energy (0.05 eV), thermal stability up to 125 °C, and transparency in UV-A, visible, and near-infrared regions. FT-IR spectroscopy demonstrated the interaction between salt and matrix in the following order: SN_E < Blend 2_E < Blend 1_E << PEO_E. The results were compared with those of acetonitrile-based liquid electrolyte, ACN_E.