Unsymmetrical Squaraine Dyes Research Articles

Novel unsymmetrical squaraine dyes for dye-sensitized solar cells: Synthesis, characterization, and comparative photovoltaic performance of USQI-NPh2Me2 and USQI-OMe

This study presents the synthesis, characterization, and photovoltaic performance of two novel unsymmetrical squaraine dyes, USQI-NPh2Me2 and USQI-OMe, engineered for application in dye-sensitized solar cells (DSSCs). These chromophores were functionalized with distinct electron-donating groups, di-p-tolylamine for USQI-NPh2Me2 and methoxy for USQI-OMe. Their molecular structures were confirmed through FT-IR, 1HNMR, 13C NMR, and mass spectrometry. Comprehensive photophysical and electrochemical studies were conducted to fine-tune the HOMO and LUMO energy levels of both dyes, optimizing charge injection into the TiO2 conduction band and facilitating dye regeneration with the iodolyte (I₃⁻/I⁻) redox mediator. USQI-NPh2Me2 exhibited a strong absorption maximum at 661 nm, achieving a high short-circuit current density (JSC) of 13.17 mA/cm2, an open-circuit voltage (VOC) of 0.71V, and an overall efficiency of 7.01 %. USQI-OMe, with its absorption peak at 651 nm, reached a JSC of 11.88 mA/cm2, a higher VOC of 0.72 V, but a slightly lower overall efficiency of 6.41 %. Both dyes demonstrated reduced aggregation on the TiO2 surface, contributing to enhanced DSSCs performance. A Comparative analysis revealed that USQI-NPh2Me2 exhibits higher efficiency, while USQI-OMe provided a greater voltage output, highlighting the influence of electron-donating groups on photovoltaic properties. These findings provide valuable insights into structure-property relationships in unsymmetrical squaraine dyes, paving the way for future DSSCs chromophore design and optimization.

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.

NIR-Sensitive Squaraine Dye-Peptide Conjugate for Trypsin Fluorogenic Detection.

Trypsin enzyme has gained recognition as a potential biomarker in several tumors, such as colorectal, gastric, and pancreatic cancer, highlighting its importance in disease diagnosis. In response to the demand for rapid, cost-effective, and real-time detection methods, we present an innovative strategy utilizing the design and synthesis of NIR-sensitive dye-peptide conjugate (SQ-3 PC) for the sensitive and selective monitoring of trypsin activity by fluorescence ON/OFF sensing. The current research deals with the design and synthesis of three unsymmetrical squaraine dyes SQ-1, SQ-2, and SQ-3 along with a dye-peptide conjugate SQ-3-PC as a trypsin-specific probe followed by their photophysical characterizations. The absorption spectral investigation conducted on both the dye alone and its corresponding dye-peptide conjugates in water, utilizing SQ-3 and SQ-3 PC respectively, reveals enhanced dye aggregation and pronounced fluorescence quenching compared to observations in DMSO solution. The absorption spectral investigation conducted on dye only and corresponding dye-peptide conjugates in water utilizing SQ-3 and SQ-3 PC, respectively, reveals not only the enhanced dye aggregation but also pronounced fluorescence quenching compared to that observed in the DMSO solution. The trypsin-specific probe SQ-3 PC demonstrated a fluorescence quenching efficiency of 61.8% in water attributed to the combined effect of aggregation-induced quenching (AIQ) and fluorescence resonance energy transfer (FRET). FRET was found to be dominant over AIQ. The trypsin-mediated hydrolysis of SQ-3 PC led to a rapid and efficient recovery of quenched fluorescence (5-fold increase in 30 min). Concentration-dependent changes in the fluorescence at the emission maximum of the dyes reveal that SQ-3 PC works as a trypsin enzyme-specific fluorescence biosensor with linearity up to 30 nM along with the limit of detection and limit of quantification of 1.07 nM and 3.25 nM, respectively.

Triazatruxene Amine Donor-Based Visible-Light-Responsive Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells

Triazatruxene Amine Donor-Based Visible-Light-Responsive Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells

Clarifying the role of carboxyl functionality in squaraines towards aggregation and self-assembly through photophysical characterization and BSA interactions

The demand for near-infrared (NIR) probes with robust and stable fluorescence signals has surged, driven by their applications in optical sensing and bioimaging. Squraine dyes as NIR fluorescent probes have gained significant traction. However, understanding their behavior in aqueous media is important for their successful application. Herein we report the synthesis and photophysical characterization of carboxy-functionalized unsymmetrical squaraine dyes capable of light absorption and emission in the near-infrared (NIR) wavelength region. Structural variations in alkyl chain length, and spacer chain length between the primary chromophore and –COOH group were systematically introduced to investigate their impact on self-assembly in aqueous media leading to dye aggregation and their differential interactions with Bovine Serum Albumin (BSA) as a model protein. In phosphate buffer (PB) the absorption intensity decreased drastically along with pronounced shoulders due to dye aggregation leading to complete fluorescence quenching. However, in the presence of BSA, the intensity of shoulder bands reduced coupled with a sharp increase in the absorption associated with monomeric dye with the increasing concentration of BSA, indicating the prevention of dye aggregation owing to dye-BSA interactions. The prevention of dye aggregation due to dye-BSA interaction also led to a tremendous increase in the fluorescence intensities as a function of the increasing BSA concentrations. Site-selective study off BSA showed that these dyes bind preferably at Site-II using hydrophilic interactions. Thus, these dyes show great potential as FRET or fluorescent on/off probes for biosensing, non-covalent labeling of proteins, and fluorescent probes for bioimaging.

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.

Visible, Far-Red, and Near-Infrared Active Unsymmetrical Squaraine Dyes Based on Extended Conjugation within the Polymethine Framework for Dye-Sensitized Solar Cells

Visible, Far-Red, and Near-Infrared Active Unsymmetrical Squaraine Dyes Based on Extended Conjugation within the Polymethine Framework for Dye-Sensitized Solar Cells

Far-red active unsymmetrical squaraine dyes containing N-arylated indoline donors for dye sensitized solar cells.

Squaraine dyes possess sharp far-red active transition with high extinction coefficient and form aggregates on TiO2 surface. Aggregation of dyes on TiO2 has been considered as a detrimental factor for DSSC device performance, which can be controlled by appending alkyl groups to the dye structures. Hence by integrating alkylated (alkyl groups with both in-plane and out-of-plane) aryl group with indoline moiety to make it compatible with other electrolytes and for controlling the dye-aggregation, a series of squaraine acceptor-based dyes SQA4-6 have been designed and synthesized. SQA4-6 dyes showed absorption between 642 and 653 nm (λmax), photophysical and electrochemical studies indicated that the HOMO energy levels of this sets of dyes are well aligned with the potentials of I-/ and [Co(bpy)3]2+/3+ redox shuttles for better dye regeneration process. DSSC device efficiency of 3% has been achieved for SQA5 dye with iodolyte (I-/ ) electrolyte in the presence of 0.3 mM of chenodeoxycholic acid (CDCA). The IPCE profile of DSSC device fabricated with SQA4-6 dyes indicated the contribution of aggregated structures for the photocurrent generation.

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%.

Photophysical Characterization and Biointeractions of NIR Squaraine Dyes for in Vitro and in Vivo Bioimaging.

The increasing demand for reliable near-infrared (NIR) probes exhibiting enduring fluorescence in living systems and facile compatibility with biomolecules such as peptides, antibodies or proteins is driven by the increasing use of NIR imaging in clinical diagnostics. To address this demand, a series of carboxy-functionalized unsymmetrical squaraine dyes (SQ-27, SQ-212, and SQ-215) along with non-carboxy-functionalized SQ-218 absorbing and emitting in the NIR wavelength range were designed and synthesized followed by photophysical characterization. This study focused on the impact of structural variations in the alkyl chain length, carboxy functionality positioning, and spacer chain length on dye aggregation and interaction with bovine serum albumin (BSA) as a model protein. In phosphate buffer (PB), the absorption intensity of the dyes markedly decreased accompanied by pronounced shoulders indicative of dye aggregation, and complete fluorescence quenching was seen in contrast to organic solvents. However, in the presence of BSA in PB, there was a enhancement in absorption intensity while regaining the fluorescence coupled with a remarkable increase in the intensity with increasing BSA concentrations, signifying the impact of dye-BSA interactions on preventing aggregation. Further analysis of Job's plot unveiled a 2:1 interaction ratio between BSA and all dyes, while the binding studies revealed a robust binding affinity (Ka) in the order of 107/mol. SQ-212 and SQ-215 were further tested for their in vitro and in vivo imaging capabilities. Notably, SQ-212 demonstrated nonpermeability to cells, while SQ-215 exhibited easy penetration and prominent cytoplasmic localization in in vitro studies. Injection of the dyes into laboratory mice showcased their efficacy in visualization, displaying stable and intense fluorescence in tissues without toxicity, organ damage, or behavioral changes. Thus, SQ-212 and SQ-215 are promising candidates for imaging applications, holding potential for noninvasive cellular and diagnostic imaging as well as biomarker detection when coupled with specific vectors in living systems.

Enhancing photovoltaic efficiency with SQI-Br and SQI-I sensitizers: A comparative analysis

Abstract This study investigates the use of halogen bonding to enhance the effectiveness of short-circuit current density (J SC) in dye-sensitized solar cells (DSSCs). To improve the performance of DSSCs, two dyes, SQI-Br and SQI-I, based on halogen atom-functionalized unsymmetrical squaraine dyes, were designed. These dyes were tested in DSSCs using iodolyte electrolytes (Z-50 and Z-100), and their performance was further improved by the introduction of chenodesoxycholic acid (CDCA). While both dyes exhibited unique photovoltaic characteristics without CDCA, a significant improvement was observed when three equivalents of CDCA were added. The most favorable results were achieved with the SQI-I dye, three equivalents of CDCA, and iodolyte Z-100, resulting in an efficiency of 6.74%, V OC of 0.694 V, and a short-circuit current density of 13.67 mA/cm2 of DSSCs. This enhanced performance can be attributed to the presence of a σ-hole, which strengthens the interaction between the electrolyte and the dyes on the TiO2 substrate, thereby facilitating dye regeneration.

Aniline and Indoline Donors Based Far‐Red Active Unsymmetrical Squaraine Dyes for Dye Sensitized Solar Cells

AbstractIn dye‐sensitized solar cells (DSSC), controlling the dye‐aggregation on the metal‐oxide surface by appending the alkyl groups around the donor or π‐spacer unit of the dye is a potential approach to enhance DSSC efficiency. Further, rigidification of the dye structures by cyclization modulates the photophysical properties of the sensitizer. Here a series of donor‐acceptor‐donor (D‐A‐D) type far‐red active unsymmetrical squaraine dyes (SQA) have been designed and synthesized, where N,N‐dimethylaniline, methylated‐ and branched‐indoline have been used as donor units. These dyes showed absorption between 629–654 nm (λmax) with the molar extinction coefficient of 1.49–1.94×105 M−1 cm−1. Systematic enhancements in DSSC device efficiency have been observed due to the cyclization and alkyl‐groups incorporation in this set of dyes which were further enhanced with the addition of chenodeoxycholic acid (CDCA). The highest DSSC device efficiency of 4.78 % (Jsc of 8.77 mA/cm2 and Voc of 692 mV) has been achieved for SQA3. The IPCE profile of SQA dyes indicates the contribution of aggregated structures for the photocurrent generation. Further, co‐sensitization of SQA3 dye with a complementary visible light active dye AK4 showed the enhanced device efficiency of 6.27 % with panchromatic IPCE response.

Steric and Electronic Effect in Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells

Steric and Electronic Effect in Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells

Squaric Acid Core Substituted Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells: Effect of Electron Acceptors on Their Photovoltaic Performance

The design and development of sensitizing dyes possessing wide-wavelength photon harvesting encompassing visible to near-infrared (NIR) wavelength regions are unavoidable for increasing the overall efficiency of dye-sensitized solar cells (DSSCs). In this study, three far-red-sensitive squaraine sensitizers were designed computationally, synthesized, and characterized, aiming towards their suitability as a potential sensitizer for DSSCs. It has been found that the incorporation of an electron acceptor moiety in the central squaraine core brought about a red shift in the absorption maximum (λmax) and the emergence of a secondary absorption band in the blue region, thus broadening the photon-harvesting window. In addition, it also lowered the dye’s HOMO energy level enabling a facile regeneration of the photo-excited dye, which improved the photovoltaic performance of SQ-223, exhibiting a photoconversion efficiency (PCE) of 4.67%. Thereafter, to address the issue of wide-wavelength photon harvesting, DSSCs were fabricated by co-adsorbing two complementary dyes SQ-223 and D-131 in various molar ratios. The DSSC fabricated with D-131 and SQ-223 in 9:1 molar ratio displayed the best photovoltaic performance with a PCE of 5.81%, a significantly higher PCE when compared to corresponding individual dye-based DSSCs containing D-131 (3.94%) and SQ-223 (4.67%).

Design of Water-Soluble Rotaxane-Capped Superparamagnetic, Ultrasmall Fe3O4 Nanoparticles for Targeted NIR Fluorescence Imaging in Combination with Magnetic Resonance Imaging.

Integrating an NIR fluorescent probe with a magnetic resonance imaging (MRI) agent to harvest complementary imaging information is challenging. Here, we have designed water-soluble, biocompatible, noncytotoxic, bright-NIR-emitting, sugar-functionalized, mechanically interlocked molecules (MIMs)-capped superparamagnetic ultrasmall Fe3O4 NPs for targeted multimodal imaging. Dual-functional stoppers containing an unsymmetrical NIR squaraine dye interlocked within a macrocycle to construct multifunctional MIMs are developed with enhanced NIR fluorescence efficiency and durability. One of the stoppers of the axle is composed of a lipophilic cationic TPP+ functionality to target mitochondria, and the other stopper comprises a dopamine-containing catechol group to anchor at the surface of the synthesized Fe3O4 NPs. Fe3O4 NPs surface-coated with targeted NIR rotaxanes help to deliver ultrasmall magnetic NPs specifically inside the mitochondria. Two carbohydrate moieties are conjugated with the macrocycle of the rotaxane via click chemistry to improve the water solubility of MitoSQRot-(Carb-OH)2-DOPA-Fe3O4 NPs. Water-soluble, rotaxane-capped Fe3O4 NPs are used for live-cell mitochondria-targeted NIR fluorescence confocal imaging, 3D and multicolor imaging in combination with T2-weighted MRI on a 9.4 T MR scanner with a high relaxation rate (r2) of 180.7 mM-1 s-1. Biocompatible, noncytotoxic, ultrabright NIR rotaxane-capped superparamagnetic ultrasmall monodisperse Fe3O4 NPs could be a promising agent for targeted multimodal imaging applications.

Design and Synthesis of Novel NIR‐Sensitive Unsymmetrical Squaraine Dyes for Molecular Photovoltaics

Two novel near‐infrared (NIR)‐sensitive unsymmetrical squaraine dyes, SQ‐258 and SQ‐259, for their suitability as a sensitizer in dye‐sensitized solar cells (DSSCs) are designed and synthesized, followed by photophysical and photovoltaic characterizations. It is demonstrated that introducing a 1,3‐indandione acceptor unit in the central squaric acid core of SQ‐259 leads to the suppression of dye aggregation owing to its nonplanar molecular geometry and the broadening of the optical absorption and photon‐harvesting window up to 800 nm. Owing to the extended wavelength photon harvesting, SQ‐259 improves the photoconversion efficiency (PCE) compared to its SQ‐258 dye counterpart. However, despite its wide wavelength photon harvesting, the improvement in the PCE of SQ‐259 is less pronounced, and this is attributed to the small driving force for injection of electrons (0.29 eV), hampered electronic coupling, and decreased electron lifetime for resistance to recombination (7.9 ms), which is confirmed by the cyclic voltammetry, quantum chemical calculation, and electrochemical impedance spectroscopic investigations, respectively.

Visible‐Light‐Active Unsymmetrical Squaraine Dyes with 1 V of Open‐Circuit Voltage for Dye‐Sensitized Solar Cells

AbstractA series of alkyl‐group‐functionalized, aniline‐ and indoline‐donor‐based, unsymmetrical visible‐light‐active squaraine dyes, AM1‐3, were designed and synthesized. Dye‐sensitized solar cell (DSSC) devices were fabricated with both I−/I3− and [Cu(tmby)2]+/2+ electrolytes. DSSC devices sensitized with the AM1 and AM2 dyes showed relatively high‐power conversion efficiency of 7.44 % and 7.22 %, respectively with I−/I3− in the absence of chenodeoxycholic acid (CDCA) than those of the AM3 dye (5.41 %). The [Cu(tmby)2]+/2+ electrolyte along with poly(3,4‐ethylenedioxythiophene) (PEDOT) as cathode material showed excellent open‐circuit potentials (VOC) of 1030, 1025, and 1001 mV with the DSSC efficiency of 8.05 %, 7.96 %, and 5.84 %, respectively, for the AM1, AM2, and AM3 dyes in the absence of CDCA. Here, the AM1 dye exhibited the maximum DSSC efficiency of 8.05 % and VOC of 1030 mV, which is the highest obtained efficiency and VOC for the visible‐light active zwitterionic unsymmetrical‐squaraine dye with copper‐based electrolyte.

Halogen functionalized D–A–D-type unsymmetrical squaraine dyes for dye-sensitized solar cells

A series of alkyl-group-wrapped and halogen atom functionalized unsymmetrical squaraine dyes (ISQ) were designed and synthesized. A maximum DSSC device efficiency of 7.80% was achieved for iodine funtionalized ISQ-I dye in Z-150 with CDCA.

Solvent-Dependent Functional Aggregates of Unsymmetrical Squaraine Dyes on TiO2 Surface for Dye-Sensitized Solar Cells.

Alkyl group wrapped donor-acceptor-donor (D-A-D) based unsymmetrical squaraine dyes SQ1, SQ5, and SQS4 were used to evaluate the effect of sensitizing solvents on dye-sensitized solar cell (DSSC) efficiency. A drastic change in DSSC efficiency was observed when the photo-anodes were sensitized in acetonitrile (bad solvent when considering dye solubility) and chloroform (good solvent) with an Iodolyte (I-/I3-) electrolyte. The DSSC device sensitized with squaraine dyes in acetonitrile showed better photovoltaic performance with enhanced photocurrent generation and photovoltage compared to the device sensitized in chloroform. In a good sensitizing solvent, dyes with long hydrophobic alkyl chains are deleterious forming aggregates on the TiO2 surface, which results in an incident photon-to-current conversion efficiency (IPCE) response mostly from monomeric and dimeric structures. Meanwhile, a bad sensitizing solvent facilitates the formation of well-packed self-assembled structures on the TiO2 surface, which are responsible for a broad IPCE response and high device efficiencies. The photoanode sensitized in the bad sensitizing solvent showed enhanced VOC values of 642, 675, and 699 mV; JSC values of 6.38, 11.1, and 11.69 mA/cm2; and DSSC device efficiencies of 3.0, 5.63, and 6.13% for the SQ1, SQ5, and SQS4 dyes in the absence of a coadsorbent (chenodeoxycholic acid (CDCA)), respectively, which were further enhanced by CDCA addition. Meanwhile, the photoanode sensitized in the good sensitizing solvent showed relatively low photovoltaic VOC values of 640, 652, and 650 mV; JSC values of 5.78, 6.79, and 6.24 mA/cm2; and device efficiencies of 2.73, 3.35, and 3.20% for SQ1, SQ5, and SQS4 in the absence of CDCA, respectively, which were further varied with equivalents of CDCA. The best DSSC device efficiencies of 6.13 and 3.20% were obtained for SQS4 without CDCA, where the dye was sensitized in acetonitrile (bad) and chloroform (good) sensitizing solvents, respectively.

Modular TiO2‐Squaraine Dyes/Electrolyte Interface for Dye‐Sensitized Solar Cells with Cobalt Electrolyte

AbstractStrategies to diminish both charge recombination and aggregation of dyes on the photoanode by functionalizing the sensitizer with alkyl groups is the best approach to achieve high dye‐sensitized solar cell (DSSC) efficiency. Development of such a photoanode with NIR‐active dyes which is compatible with a cobalt electrolyte is important to enhance the photovoltaic performance. In this report, alkyl‐group‐wrapped donor‐acceptor‐donor (D‐A‐D) based unsymmetrical squaraine dyes have been used for DSSC device characterization with a cobalt electrolyte. Surface passivation of photoanode was varied systematically by the extent of functionalization with alkyl groups to avoid charge recombination. DSSC device performance of 5.92 % was achieved for an alkyl‐group‐wrapped squaraine dye with a cobalt electrolyte. Hence, appending the alkyl groups on the donor unit of squaraine dyes helps passivating the photoanode, whereas introducing hydrophilic groups provides a leaky surface where oxidized electrolyte species reach the titanium‐metal‐oxide surface which promotes the charge recombination process.