High Extinction Coefficient Research Articles

Combined experimental and DFT investigation on photovoltaic performance of low-cost metal-free organic dye-sensitized solar cells

Metal-free organic dyes, viz. eosin yellow (eosin-Y), fluorescein and curcumin were used as sensitizers in zinc oxide (ZnO) nanoparticles thin film photoanode based dye-sensitized solar cell (DSSC) and also investigated by density functional theory (DFT). UV–vis spectrophotometer was employed to determine absorption feature of dyes in solar spectrum, adsorption tendency towards ZnO photoanode surface, molar-extinction coefficient and desorbed dye molecules from the photoanode surface. The photovoltaic performance of metal-free organic DSSCs employing imidazole based liquid electrolyte and platinum counter electrode was evaluated under standard light exposure of 85 mW/cm2. Among the dyes, eosin-Y DSSC delivered overall energy conversion efficiency (η) of 0.95 % with short-circuit photocurrent density (Jsc) of 2.98 mA cm−2, open-circuit photovoltage (Voc) of 0.54 V and fill factor (FF) of 0.50, which was about 20 % and 40 % higher than that of the energy conversion efficiency of DSSCs sensitized with fluorescein and curcumin dyes, respectively. The better photovoltaic performance exhibited by the eosin-Y DSSC is credited to its high molar extinction coefficient, intense light absorption in the solar spectrum and good adsorption on ZnO thin film photoanode surface. The maximum driving force for dye molecules regeneration and electron injection value of eosin-Y dye attached on the surface of ZnO cluster (eosin-Y + ZnO) resulted in higher Voc. The outcomes of this experimental data are in well agreement with DFT results.

Thermally stable high carrier mobility nanocomposite infrared photodetector

Quantum dots (QDs) show excellent optical properties, such as a high extinction coefficient, tunable colors, and superior photostability. However, the transport properties of QDs, such as carrier mobility, are quite limited, which hinder optoelectronic applications. On the other hand, carbon nanotubes (CNTs) generally have high carrier mobility and thermal stability with a weak optical response. These features inspire us to couple QDs with CNTs to achieve improved optoelectronics. We take infrared HgTe QDs and multi-walled CNTs as examples. With appropriate coupling between QD and CNT matrices, carrier mobility could reach 34.6–54.1 cm2/Vs in the nanocomposite, a 1000-fold increase compared with the reference. The nanocomposite benefits external quantum efficiency up to 12 500% and detectivity 1012 Jones on the 2500 nm infrared photodetectors. The CNT matrix also helps relaxing thermally generated carriers, improving the photodetector thermal stability. We also demonstrate that the device maintains high detectivity at a high operating temperature.

Sunlight sparks spectacular C(sp3)─H bond arylation: Rod shape ACC@MeF composite shines bright in 2,4‐dinitrophenylhydrazine reaction

AbstractThe solar light responsive selective C(sp3)─H bond activation by photocatalytic pathway using graphene platform as photocatalyst is a green and sustainable route to achieve value‐added chemicals on gram scale synthesis. Graphene has low activity due to fast recombination charges, band gap suitability problems, and inefficient solar light absorption ability. Therefore, activated carbon cloth‐based nitrogen‐rich phenolic resin was developed from melem and formaldehyde. The ACC@MeF light‐harvesting composite demonstrates outstanding light‐harvesting capability, leading to enhanced photocatalytic performance in C(sp3)─H bond formation, suitability of band gap, high molar extinction coefficient and high thermal stability. The development of metal‐free activated carbon cloth‐based melem formaldehyde resin for the solar light photocatalytic transformation of organic compounds is anticipated to have broad‐reaching applications.

Novel Beta-Functionalized Porphyrins Approaching 11% Efficiency for Organic Solar Cells.

Porphyrins and their derivatives possess high molar extinction coefficients and strong electron-donating abilities and have been widely used in organic solar cells (OSCs). Though porphyrins can be easily functionalized at the four meso-positions and the eight β-positions, nearly all porphyrin photovoltaic materials are reported to be functionalized at the meso-positions, and the porphyrin photovoltaic materials functionalized at the β-positions are to be explored. Herein, the regioselective β-positions of a porphyrin are first brominated without using rare metal iridium catalysts, and then, after two more reactions, two antipodal β-substituted porphyrin donors EHDPP-Por and BODPP-Por are synthesized, in which four DPP (diketopyrrolopyrrole) units are connected symmetrically with acetylene at four of the β-positions, for OSCs. The all-small-molecule organic solar cells based on EHDPP-Por:Y6 and BODPP-Por:Y6 active layers achieved power conversion efficiencies of 10.19 and 10.99%, respectively, which are higher than most of the binary OSCs based on the porphyrins functionalized at the meso-positions, demonstrating that β-functionalized porphyrins are very promising for OSCs.

An electrochemiluminescence sensor based on lanthanide bimetallic MOFs with a “cascade sensitization mechanism” for the sensitive detection of CA242

Lanthanide metal-organic frameworks (Ln-MOFs) broaden the optical sensing applications of lanthanide ions due to the antenna effect between organic ligands and metals. However, the sensitization ability of the ligand to metal ions is limited, and maximizing the sensitization of the electrochemiluminescence behavior of Eu3+ is still a challenge for the application of Ln-MOFs. Therefore, under the guidance of the “cascade sensitization mechanism” based on the antenna effect sensitizing the electrochemiluminescence of bimetallic Ln-MOFs, we proposed Eu/Tb-MOFs with high luminescence intensity as a signal probe. According to the antenna effect, the conjugated structure and high extinction coefficient of the benzene ring of 2-amino terephthalic acid (NH2-BDC) can enhance the ECL luminescence intensity of Eu/Tb-MOFs. Tb3+ can act as an energy bridge between NH2-BDC and Eu3+, buffering the energy gap. The bimetallic sensitization is formed between Tb3+ and Eu3+, which can inhibit the reverse internal flow of energy and ensure the high luminous efficiency of Eu3+. In addition, the nanosphere mixed valence Fe3O4 as a co-reactant accelerator promotes the formation of transient free radical SO4•- through the valence change of Fe2+/Fe3+. The ECL immunosensor constructed by luminophores Eu/Tb-MOFs and nanosphere Fe3O4 provided a new explanation for the ECL self-luminous of Eu/Tb-MOFs.

Multi-scale CuS-rGO pyramidal photothermal structure for highly efficient solar-driven water evaporation and thermoelectric power generation

Integrated water evaporation and thermoelectric power generation system (IWETPGS) has been recognized to be a promising strategy for the utilization of solar energy. Herein, we developed a new type of IWETPGS with multi-scale pyramidal photothermal structures. They featured three-dimensional pyramidal structures with microscale gradient porous copper foams, as well as micro/nanoscale CuS nanowires and reduced graphene oxide (rGO) composite materials. They combined the merits of efficient multiple refraction and absorption of light, broad-spectrum absorption capabilities of rGO and high near-infrared extinction coefficient of CuS, as well as fast water transportation by gradient porous matrix. These photothermal structures induced a photothermal conversion efficiency of 97.6%. An IWETPGS integrating these structures with a thermoelectric generator (TEG) and microchannel heat sink was developed, and outstanding evaporation and output power performance were obtained simultaneously with an evaporation rate of 2.29 kg/m2h and maximum output power of 1.32 W/m2 under 1 sun illumination. Outdoor tests showed that an average daily water production of 12.1 kg/m2 and a maximum power generation of 5.55 W/m2 was obtained. This work provides a high-performance multi-scale CuS-rGO pyramidal photothermal structure to achieve freshwater and thermoelectric power co-generation, which provides potential opportunities for freshwater and electricity supply in remote areas.

Synthesis and Photophysical Properties of β-Alkenyl-Substituted BODIPY Dyes by Indium(III)-Catalyzed Intermolecular Alkyne Hydroarylation.

A new atom-economical synthesis of β-alkenyl-substituted BODIPYs via indium(III)-catalyzed intermolecular alkyne hydroarylation with meso-substituted BODIPYs is described. While catalysis with InI3 allows the double β-functionalization of BODIPY, resulting in regioselectively branched β,β'-disubstituted alkenyl BODIPYs, catalytic InCl3 enables the formation of linear β-substituted alkenyl BODIPYs. Subsequent In(III)-catalyzed intermolecular alkyne hydroarylation allows the synthesis of unsymmetrical push-pull BODIPY derivatives. Therefore, indium catalysis offers complementary regioselectivity in good chemical yields and functional group tolerance. The resulting BODIPY dyes displayed bathochromically shifted absorption and emission according to the electron-nature of the substituents in the alkenyl moiety with high molar extinction coefficients (ε up to 88,200 M-1 cm-1) and quantum yields (0.14-0.96).

Tumor-Targeted Squaraine Dye for Near-Infrared Fluorescence-Guided Photodynamic Therapy.

Many efforts have been made to develop near-infrared (NIR) fluorescent dyes with high efficiency for the NIR laser-induced phototherapy of cancer. However, the low tumor targetability and high nonspecific tissue uptake of NIR dyes in vivo limit their applications in preclinical cancer imaging and therapy. Among the various NIR dyes, squaraine (SQ) dyes are widely used due to their high molar extinction coefficient, intense fluorescence, and excellent photostability. Previously, benzoindole-derived SQ (BSQ) was prepared by incorporating carboxypentyl benzoindolium end groups into a classical SQ backbone, followed by conjugating with cyclic RGD peptides for tumor-targeted imaging. In this study, we demonstrate that the structure-inherent tumor-targeting BSQ not only shows a high fluorescence quantum yield in serum but also exhibits superior reactive oxygen species (ROS) generation capability under the 671 nm laser irradiation for effective photodynamic therapy (PDT) in vitro and in vivo. Without targeting ligands, the BSQ was preferentially accumulated in tumor tissue 24 h post-injection, which was the optimal timing of the laser irradiation to induce increments of ROS production. Therefore, this work provides a promising strategy for the development of photodynamic therapeutic SQ dyes for targeted cancer therapy.

High-Density Au Anchored to Ti3C2-Based Colorimetric-Fluorescence Dual-Mode Lateral Flow Immunoassay for All-Domain-Enhanced Performance and Signal Intercalibration.

In this work, a novel MXene-Au nanoparticle (Ti3C2@Au) was synthesized with a high molar extinction coefficient, strong fluorescence quenching ability, ultrahigh antibody affinity, high stability, and good dispersibility, and it was used to develop a colorimetric-fluorescence dual-mode lateral flow immunoassay (LFIA). The detection limits of this method for the detection of dexamethasone in milk, beef, and pork were 0.0018, 0.12, and 0.084 μg/kg in the "turn-off" mode (colorimetric signal), and 0.0013, 0.080, and 0.070 μg/kg in the "turn-on" mode (fluorescent signal), respectively, which was up to 231-fold more sensitive compared with that of the reported LFIAs. The recovery rates ranged from 81.1-113.7%, and 89.2-115.4%, with the coefficients of variation ranging from 1.4-15.0%, and 1.9-14.8%, respectively. The results of the LC-MS/MS confirmation test on 30 real samples had a good correlation with that of our established method (R2 > 0.97). This work not only developed novel nanocarriers for antibody-based LFIA but also ensured high-performance detection.

Arsenic field test kits based on solid-phase fluorescence filter effect induced by silver nanoparticle formation

Millions of people worldwide are affected by naturally occurring arsenic in groundwater. The development of a low-cost, highly sensitive, portable assay for rapid field detection of arsenic in water is important to identify areas for safe wells and to help prioritize testing. Herein, a novel paper-based fluorescence assay was developed for the on-site analysis of arsenic, which was constructed by the solid-phase fluorescence filter effect (SPFFE) of AsH3-induced the generation of silver nanoparticles (AgNPs) toward carbon dots. The proposed SPFFE-based assay achieves a low arsenic detection limit of 0.36 μg/L due to the efficient reduction of Ag+ by AsH3 and the high molar extinction coefficient of AgNPs. In conjunction with a smartphone and an integrated sample processing and sensing platform, field-sensitive detection of arsenic could be achieved. The accuracy of the portable assay was validated by successfully analyzing surface and groundwater samples, with no significant difference from the results obtained through mass spectrometry. Compared to other methods for arsenic analysis, this developed system offers excellent sensitivity, portability, and low cost. It holds promising potential for on-site analysis of arsenic in groundwater to identify safe well locations and quickly obtain output from the global map of groundwater arsenic.

Development of organic co-sensitizers based on piperonal for over 10% efficient ruthenium complex dye-sensitized solar cells

In this study, two new piperonal-based organic dyes, designated D-1–2, were synthesized for use in dye-sensitized solar cells (DSSCs). The dyes studied have a D-π-A configuration and have undergone molecular engineering to fine-tune their spectral properties and energy levels. A comprehensive analysis involving both experimental and theoretical approaches was performed to investigate their optical, electrochemical, photovoltaic, geometrical, and electronic features. These newly developed dyes exhibit notably strong UV–vis absorption, with high molar extinction coefficients, making them an attractive option as co-sensitizers for ruthenium-based dye-sensitized solar cells (DSSCs). Co-sensitization at a concentration of 0.2 mM resulted in a significant increase in the PCEs of DSSCs, ranging from 7.90 % to 10.43 %, compared to the PCE of 7.31 % for DSSCs sensitized solely with N719. The improvement in PCEs can be attributed to the enhanced JCSS and Voc achieved through co-sensitization, highlighting the potential benefits of utilizing co-sensitizers to develop more efficient DSSCs. The highest PCE achieved was 10.43 %, with a Jsc of 19.05 mA.cm−2 and a VOC of 750 mV for the mixed co-sensitizers (D-1 + D-2 + N719). These findings indicate that cocktail co-sensitization is a promising strategy for constructing efficient D-π-A-type sensitizers and for evaluating the performance of DSSCs. Additionally, incident photon-to-current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) studies provide insights into the mechanisms responsible for these improvements. Based on the IPCE study, the increase in Jsc during co-sensitization is due to less photocurrent loss from the electrolyte. EIS experiments showed that making a monolayer of sensitizers that was denser and more organized probably led to less electron recombination between the injected electrons and the electrolyte. This could be because the dyes were absorbed more. The findings of this study suggest that D-1–2 co-sensitizers might be game-changers in the development of more effective DSSCs. In addition, this investigation provides crucial information regarding the underlying systems.

Photon Upconversion at Organic-Inorganic Interfaces.

Photon upconversion is a process that combines low-energy photons to form useful high-energy photons. There are potential applications in photovoltaics, photocatalysis, biological imaging, etc. Semiconductor quantum dots (QDs) are promising for the absorption of these low-energy photons due to the high extinction coefficient of QDs, especially in the near infrared (NIR). This allows the intriguing use of diffuse light sources such as solar irradiation. In this review, we describe the development of this organic-QD upconversion platform based on triplet-triplet annihilation, focusing on the dark exciton in QDs with triplet character. Then we introduce the underlying energy transfer steps, starting from QD triplet photosensitization, triplet exciton transport, triplet-triplet annihilation, and ending with the upconverted emission. Design principles to improve the total upconversion efficiency are presented. We end with limitations in current reports and proposed future directions. This review provides a guide for designing efficient organic-QD upconversion platforms for future applications, including overcoming the Shockley-Queisser limit for more efficient solar energy conversion, NIR-based phototherapy, and diagnostics in vivo.

Efficient Photothermal Sensor Based on Coral-Like Hollow Gold Nanospheres for the Sensitive Detection of Sulfonamides.

Gold nanoparticles (AuNPs), universally regarded as colorimetric signal reporters, are widely employed in lateral flow immunoassays (LFIAs). However, it is difficult for AuNPs-LFIA to achieve a wide range and sensitive detection. Herein, novel coral-like hollow gold nanospheres (CHGNPs) are synthesized. The growth of gold nanospheres can be regulated to obtain a multibranched and hollow construction. The obtained CHGNPs possess intense broadband absorption across the visible to near-infrared region, exhibiting a high molar extinction coefficient of 14.65×1011 M-1 cm-1 and a photothermal conversion efficiency of 79.75%. Thus, the photothermal/colorimetric dual-readout LFIA is developed based on CHGNPs (CHGNPs-PT-LFIA and CHGNPs-CM-LFIA) to effectively improve the detection sensitivity and broaden the detection range in regard to sulfonamides (SAs). The limits of detection of the CHGNPs-PT-LFIA and CHGNPs-CM-LFIA reached 1.9 and 2.8pgmL-1 for the quantitative detection of sulfaquinoxaline, respectively, which are 6.3-fold and 4.3-fold lower than that of the AuNPs-LFIA. Meanwhile, the CHGNPs-PT-LFIA broadened the detection range to three orders of magnitude, which ranged from 2.5 to 5000 pg mL-1. The synthesized photothermal CHGNPs have been proven effective in improving the performance of the LFIA and provide a potential option for the construction of sensing platforms.

Red phenanthrenequinone dyes with high thermal and photo-stability for LCD color filters

Color filters (CF) are essential integral parts of the liquid crystal display (LCD) and image sensor. Compared to traditional pigment colorants, organic dyes offer a promising alternative to realize CF with improved optical properties and higher resolution. However, organic dyes usually suffer from inferior thermal and photo-stability, limiting their applications in CF. Herein, four robust donor-acceptor organic dyes based on phenanthrenequinone chromophore were designed and synthesized by introducing aromatic amine derivatives as the electron donors. The strong donor-acceptor interactions in these dyes contribute to intense broad charge-transfer absorption bands from 375 nm to 600 nm with high molar extinction coefficients, thus realizing red color. Also, these dyes exhibit high thermal and photo-stability, good compatibility with the polymer binder and low aggregation tendencies, resulting in high thermal and photo-stability for the fabricated CF films. Remarkably, among these phenanthrenequinone dyes, DTPAP with multi-donor substitution and extended π-conjugation exhibited the best performance in terms of molar extinction coefficient, thermal and photo-stability, contributing to the highest thermal and photo-stability for the CF film with color difference values (ΔEab) below 0.75 under simulated industrial manufacturing processes. This work confirms that phenanthrenequinone is a robust chromophore and is conducive to developing thermal and photo-stable CF dyes, and paves a way to improve the optical properties and stability of donor-acceptor dyes for CF.

Targeted Cyclo[8]pyrrole-Based NIR-II Photoacoustic Tomography Probe for Suppression of Orthotopic Pancreatic Tumor Growth and Intra-abdominal Metastases.

Pancreatic cancer is highly lethal. New diagnostic and treatment modalities are desperately needed. We report here that an expanded porphyrin, cyclo[8]pyrrole (CP), with a high extinction coefficient (89.16 L/g·cm) within the second near-infrared window (NIR-II), may be formulated with an αvβ3-specific targeting peptide, cyclic-Arg-Gly-Asp (cRGD), to form cRGD-CP nanoparticles (cRGD-CPNPs) with promising NIR-II photothermal (PT) therapeutic and photoacoustic (PA) imaging properties. Studies with a ring-array PA tomography system, coupled with analysis of control nanoparticles lacking a targeting element (CPNPs), revealed that cRGD conjugation promoted the delivery of the NPs through abnormal vessels around the tumor to the solid tumor core. This proved true in both subcutaneous and orthotopic pancreatic tumor mice models, as confirmed by immunofluorescent studies. In combination with NIR-II laser photoirradiation, the cRGD-CPNPs provided near-baseline tumor growth inhibition through PTT both in vitro and in vivo. Notably, the combination of the present cRGD-CPNPs and photoirradiation was found to inhibit intra-abdominal metastases in an orthotopic pancreatic tumor mouse model. The cRGD-CPNPs also displayed good biosafety profiles, as inferred from PA tomography, blood analyses, and H&E staining. They thus appear promising for use in combined PA imaging and PT therapeutic treatment of pancreatic cancer.

Tuning Shortwave‐Infrared J‐aggregates of Aromatic Ring‐Fused Aza‐BODIPYs by Peripheral Substituents for Combined Photothermal and Photodynamic Therapies at Ultralow Laser Power

AbstractAchieving photothermal therapy (PTT) at ultralow laser power density is crucial for minimizing photo‐damage and allowing for higher maximum permissible skin exposure. However, this requires photothermal agents to possess not just superior photothermal conversion efficiency (PCE), but also exceptional near‐infrared (NIR) absorptivity. J‐aggregates, exhibit a significant redshift and narrower absorption peak with a higher extinction coefficient. Nevertheless, achieving predictable J‐aggregates through molecular design remains a challenge. In this study, we successfully induced desirable J‐aggregation (λabsmax: 968 nm, ϵ: 2.96×105 M−1 cm−1, λemmax: 972 nm, ΦFL: 6.2 %) by tuning electrostatic interactions between π‐conjugated molecular planes through manipulating molecular surface electrostatic potential of aromatic ring‐fused aza‐BODIPY dyes. Notably, by controlling the preparation method for encapsulating dyes into F‐127 polymer, we were able to selectively generate H‐/J‐aggregates, respectively. Furthermore, the J‐aggregates exhibited two controllable morphologies: nanospheres and nanowires. Importantly, the shortwave‐infrared J‐aggregated nanoparticles with impressive PCE of 72.9 % effectively destroyed cancer cells and mice‐tumors at an ultralow power density of 0.27 W cm−2 (915 nm). This phototherapeutic nano‐platform, which generates predictable J‐aggregation behavior, and can controllably form J‐/H‐aggregates and selectable J‐aggregate morphology, is a valuable paradigm for developing photothermal agents for tumor‐treatment at ultralow laser power density.

Tuning Shortwave-Infrared J-aggregates of Aromatic Ring-Fused Aza-BODIPYs by Peripheral Substituents for Combined Photothermal and Photodynamic Therapies at Ultralow Laser Power.

Achieving photothermal therapy (PTT) at ultralow laser power density is crucial for minimizing photo-damage and allowing for higher maximum permissible skin exposure. However, this requires photothermal agents to possess not just superior photothermal conversion efficiency (PCE), but also exceptional near-infrared (NIR) absorptivity. J-aggregates, exhibit a significant redshift and narrower absorption peak with a higher extinction coefficient. Nevertheless, achieving predictable J-aggregates through molecular design remains a challenge. In this study, we successfully induced desirable J-aggregation (λabs max : 968 nm, ϵ: 2.96×105 M-1 cm-1 , λem max : 972 nm, ΦFL : 6.2 %) by tuning electrostatic interactions between π-conjugated molecular planes through manipulating molecular surface electrostatic potential of aromatic ring-fused aza-BODIPY dyes. Notably, by controlling the preparation method for encapsulating dyes into F-127 polymer, we were able to selectively generate H-/J-aggregates, respectively. Furthermore, the J-aggregates exhibited two controllable morphologies: nanospheres and nanowires. Importantly, the shortwave-infrared J-aggregated nanoparticles with impressive PCE of 72.9 % effectively destroyed cancer cells and mice-tumors at an ultralow power density of 0.27 W cm-2 (915 nm). This phototherapeutic nano-platform, which generates predictable J-aggregation behavior, and can controllably form J-/H-aggregates and selectable J-aggregate morphology, is a valuable paradigm for developing photothermal agents for tumor-treatment at ultralow laser power density.

Sunlight stability enhancement of camphorquinone based photo-curing materials via [2 + 2] cycloaddition of pyrrole ketene

High photo-resistance and photo-sensitivity is a persistent challenge in photopolymerization. In this research, sunlight stability of commercial photoinitiator camphorquinone (CQ) based photo-curing materials is enhanced by adding the mixture of (E)-1-(cyclohex-1-en-1-yl)-3-(1H-pyrrol-2-yl)prop-2-en-1-one (E-CHPO) and its cis isomer Z-CHPO used as a solution mask. These compounds have a broad absorption range and a high molar extinction coefficient, ranging from 250 nm to 550 nm, which inhibits the action of CQ. Furthermore, CQ could also absorb light for polymerization as E/Z-CHPO gradually fades due to its [2 + 2] cycloaddition reaction under LED@465 nm irradiation with high light intensity. Additionally, corresponding mechanism was investigated.

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.

Nanotubular TiO2 films sensitized with CdTe quantum dots: Stability and adsorption distribution

Quantum dots (QDs) are zero-dimensional nanostructured semiconductors that are widely studied for their size and shape dependent optical behavior, making them attractive for numerous applications, including photovoltaics. Within this group of nanomaterials, CdTe QDs represent an interesting material as a sensitizer for TiO2 (Nt-TiO2) nanotubular matrices due to their bulk band gap of 1.45 eV and their high extinction coefficient. However, its functionality may be limited, being unstable in the presence of some redox probes due to photocorrosion processes. In this work, the composition and internal distribution of CdTe QDs adsorbed on Nt-TiO2 from toluene and toluene/acetone (70:30) and (50:50) mixtures were studied by X-ray photoelectron spectroscopy (XPS), before and after photocurrent measurements.XPS was used to characterize the coverage and distribution of QDs along the Nt-TiO2. It is shown that the increased polarity of the solvent causes a higher coverage and an extended distribution of QDs toward the interior of Nt-TiO2, which causes the photogenerated electrons to travel shorter distances to reach the underneath electrical contact, thus achieving a higher photocurrent. Additionally, the photoanode shows a progressive decrease in the Te signals inside the nanotubes after the photocurrent recording, presumably due to a photocorrosion process in the presence of Na2S and illumination.