A Cu(2)S-CuInS(2)-ZnSe quantum dot (QD)-sensitized solar cell with cascaded energy gap structures has been fabricated. Under simulated illumination (AM 1.5, 100 mW cm(-2)), the best device is obtained with a Cu(2)S-CuInS(2)-ZnSe QD-sensitized solar cell, yielding a power conversion efficiency of 2.52%.

This article describes a CuInS2 quantum dot (QD)-sensitized solar cell (QDSSC) with a multilayered architecture and a cascaded energy-gap structure fabricated using a successive ionic-layer adsorption and reaction process. We initially used different metal chalcogenides as interfacial buffer layers to improve unmatched band alignments between the TiO2 and CuInS2 QD sensitizers. In this design, the photovoltaic performance, in terms of the short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), and power conversion efficiency (PCE), was significantly improved. Both JSC and VOC were improved in CuInS2-based QDSSCs in the presence of interfacial buffer layers because of proper band alignment across the heterointerface and the negative band edge movement of TiO2. The PCE of CuInS2-based QDSSCs containing In2Se3 interfacial buffer layers was 1.35%, with JSC=5.83 mA/cm2, VOC=595 mV, and FF=39.0%. We also examined the use of alternative CdS and CdSe hybrid-sensitized layers, which were sequentially deposited onto the In2Se3/CuInS2 configuration for creating favorable cascaded energy-gap structures. Both JSC (11.3 mA cm(-2)) and FF (47.3%) for the CuInS2/CdSe hybrid-sensitized cells were higher than those for CuInS2-based cells (JSC=5.83 mA cm(-2) and FF=39.0%). In addition, the hybrid-sensitized cells had PCEs that were 1.3 times those of cells containing identically pretreated In2Se3 interfacial buffer layers. Additionally, we determined that ZnSe served as a good passivation layer on the surface of CuInS2/CdSe hybrid-sensitized QDs, prevented current leakage from the QDs to electrolytes, and lowered interfacial charge recombination. Under simulated illumination (AM 1.5, 100 mW cm(-2)), multilayered QDSSCs with distinct architectures delivered a maximum external quantum efficiency of 80% at 500 nm and a maximum PCE of 4.55%, approximately 9 times that of QDSSCs fabricated with pristine CuInS2.

A cadmium-free CuInS2 quantum dot (QD)-sensitized solar cell (QDSC) has been fabricated by taking advantage of the ex situ synthesis approach for fabricating highly crystalline QDs and the in situ successive ionic-layer adsorption and reaction (SILAR) approach for achieving high surface coverage of QDs. The ex situ synthesized CuInS2 QDs can be rendered water soluble through a simple and rapid two-step method under the assistance of ultrasonication. This approach allows a stepwise ligand change from the insertion of a foreign ligand to ligand replacement, which preserves the long-term stability of colloidal solutions for more than 1 month. Furthermore, the resulting QDs can be utilized as sensitizers in QDSCs, and such a QDSC can deliver a power conversion efficiency (PCE) of 0.64%. Using the SILAR process, in situ CuInS2 QDs could be preferentially grown epitaxially on the pre-existing seeds of ex situ synthesized CuInS2 QDs. The results indicated that the CuInS2 QDSC fabricated by the combined ex situ/in situ growth process exhibited a PCE of 1.84% (short-circuit current density = 7.72 mA cm(-2), open-circuit voltage = 570 mV, and fill factor = 41.8%), which is higher than the PCEs of CuInS2 QDSCs fabricated by ex situ and in situ growth processes, respectively. The relative efficiencies of electrons injected by the combined ex situ/in situ growth approach were higher than those of ex situ synthesized CuInS2 QDs deposited on TiO2 films, as determined by emission-decay kinetic measurements. The incident photon-to-current conversion efficiency has been determined, and electrochemical impedance spectroscopy has been carried out to investigate the photovoltaic behavior and charge-transfer resistance of the QDSCs. The results suggest that the combined synergetic effects of in situ and ex situ CuInS2 QD growth facilitate more electron injection from the QD sensitizers into TiO2.

In this study, bimetallic platinum/gold nanoparticles (Pt/Au NPs) were found to exhibit peroxidase-like activity, and the deposition of mercury was found to switch the enzymatic activity to a catalase-like activity. Based on this phenomenon, we developed a new method for detecting mercury ions through their deposition on bimetallic Pt/Au NPs to switch the catalytic activity of Pt/Au NPs. Pt/Au NPs could be easily prepared through reduction of Au(3+) and Pt(4+) by sodium citrate in a one-pot synthesis. The peroxidase catalytic activity of the Pt/Au NPs was controlled by varying the ratios of Pt to Au. The Pt(0.1)/Au NPs (prepared with a [Au(3+)]/[Pt(4+)] molar ratio of 9.0/1.0) showed excellent oxidation catalysis for H(2)O(2)-mediated oxidation of Amplex® Red (AR) to resorufin. The oxidized product of AR, resorufin, fluoresces more strongly (excitation/emission wavelength maxima ca. 570/585 nm) than AR alone. The peroxidase catalytic activity of Pt(0.1)/Au NPs was switched to catalase-like activity in the presence of mercury ions in a 5.0 mM tris(hydroxymethyl)aminomethane (Tris)-borate solution (pH 7.0) through the deposition of Hg on the particle surfaces owing to the strong Hg-Au metallic bond. The catalytic activity of Hg-Pt(0.1)/Au NPs is superior (by at least 5-fold) to that of natural catalase (from bovine liver). Under optimal solution conditions [5.0 mM Tris-borate (pH 7.0), H(2)O(2) (50 mM), and AR (10 μM)] and in the presence of the masking agents polyacrylic acid and tellurium nanowires, the Pt(0.1)/Au NPs allowed the selective detection of inorganic mercury (Hg(2+)) and methylmercury ions (MeHg(+)) at concentrations as low as several nanomolar. This simple, fast, and cost-effective system enabled selective determination of the spiked concentrations of Hg(2+) and MeHg(+) in tap, pond, and stream waters.

The surface of Ti3C2 MXene nanosheets (TC NSs) was first modified with the antioxidants sodium ascorbate (SA) and dopamine (DA) (DSTC NS) to improve their stability in oxidative and hydration environments and thereby improve their bioapplications. This novel approach not only improved MXene stability by arresting oxidation but also increased the available functional groups for further functionalization with various biomolecules. The DSTC NSs were then sequentially conjugated with enzyme glucose oxidase (GOx) and photosensitizer Ce6 to render the obtained CGDSTC NSs with glucose starvation and photodynamic therapeutic properties and thus attain high efficiency in killing cancer cells through the cooperative effect. The as-synthesized CGDSTC NSs demonstrated tremendous photothermal effect with conversion efficiency of 45.1% and photodynamic (ROS generation) properties upon irradiation with 808 and 671 nm lasers. Furthermore, it was observed that the enzymatic activity of CGDSTC NSs increased upon laser irradiation due to enhanced solution temperature. During in vitro studies, the CGDSTC NSs exhibited cytocompatability to HePG2 and HeLa cells under nonstimulus conditions. However, they elicited more than 90% cell-killing efficiency in the presence of glucose and laser irradiation via the cooperative effect between starvation therapy and phototherapy. These results indicate that CGDSTC NSs could be used as potential therapeutic agents to eradicate cancers with no or few adverse effects. This surface modification approach is also simple and facile to adopt in MXene-based research.