2D Ti3C2-MXene Serving as Intermediate Layer between Absorber and Back Contact for Efficient CZTSSe Solar Cells.

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) has been considered as the most promising absorber material for inorganic thin-film solar cells. Among the three main interfaces in CZTSSe-based solar cells, the CZTSSe/Mo back interface plays an essential role in hole extraction as well as device performance. During the selenization process, the reaction between CZTSSe and Mo is one of the main reasons that lead to a large open circuit voltage (VOC) deficit, low short circuit current (Jsc), and fill factor. In this study, 2D Ti3C2-MXene was introduced as an intermediate layer to optimize the interface between the CZTSSe absorber layer and Mo back contact. Benefiting from the 2D Ti3C2-MXene intermediate layer, the reaction between CZTSSe and Mo was effectually suppressed, thus, significantly reducing the thickness of the detrimental Mo(S,Se)2 layer as well as interface recombination at the CZTSSe/Mo back interface. As a result, the power conversion efficiency of the champion device fabricated with the 2D Ti3C2-MXene intermediate layer was improved from 10.89 to 13.14% (active-area efficiency). This study demonstrates the potential use of the 2D Ti3C2-MXene intermediate layer for efficient CZTSSe solar cells and promotes a deeper understanding of the back interface in CZTSSe solar cells.

Suppressing interface recombination in CZTSSe solar cells by simple selenization with synchronous interface gradient doping.

The main bottleneck in the development of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is their very low VOC due to severe carrier recombination. Specifically, due to the poor defect environment and unfavorable band structure, carrier recombination at the front interface is considered to be one of the most serious issues. Thus, to reduce the interface recombination and VOC deficit, we propose a convenient and effective strategy for Cd gradient doping near the front interface during selenization. The formed Cd gradient significantly reduced the CuZn defects and related [2CuZn + SnZn] defect clusters near the CZTSSe-CdS heterojunction, thus significantly suppressing the interface recombination near the heterojunction. Benefitting from the formed Cd gradient, a champion device with 12.14% PCE was achieved with the VOC significantly improved from 432 mV to 486 mV. The proposed element gradient doping strategy can offer a new idea for selenization and element gradient doping in other photoelectric devices.

ZnO nanotubes supported molecularly imprinted polymers arrays as sensing materials for electrochemical detection of dopamine.

In this study, ZnO nanotubes (ZNTs) were prepared onto fluorine-doped tin oxide (FTO) glass and used as supports for MIPs arrays fabrication. Due to the imprinted cavities are always located at both inner and outer surface of ZNTs, these ZNTs supported MIPs arrays have good accessibility towards template and can be used as sensing materials for chemical sensors with high sensitivity, excellent selectivity and fast response. Using K3[Fe(CN)6] as electron probe, the fabricated electrochemical sensor shows two linear dynamic ranges (0.02-5µM and 10-800µM) towards dopamine. This proposed electrochemical sensor has been applied for dopamine determination with satisfied recoveries and precision. More complex human urine samples also confirmed that the proposed method has good accuracy for dopamine determination in real biological samples. These results suggest potential applicability of the proposed method and sensor in important molecule analysis.

p-type Li, Cu-codoped NiOx hole-transporting layer for efficient planar perovskite solar cells.

p-type inorganic hole transport materials of Li, Cu-codoped NiOx films were deposited using a simple solution-based process. The as-prepared films were used as hole selective contacts for lead halide perovskite solar cell. An enhanced power conversion efficiency of 14.53% has been achieved due to the improved electrical conductivity and optical transmittance of the Li, Cu-codoped NiOx electrode interlayer.

Phase-dependent photocatalytic H2 evolution of copper zinc tin sulfide under visible light.

CZTS exhibited apparently phase-dependent photocatalytic H2 evolution under visible light. Possible factors for the phase-dependent photocatalytic activity of CZTS were discussed in detail.

Cu2ZnSnSe4 nanocrystals capped with S(2-) by ligand exchange: utilizing energy level alignment for efficiently reducing carrier rec ombination.

In this work, we employed a convenient one-step synthesis method for synthesizing Cu2ZnSnSe4 (CZTSe) nanocrystals (NCs) in an excess selenium environment. This excess selenium situation enhanced the reaction of metal acetylacetonates with selenium, resulting in the burst nucleation of NCs at relatively low temperatures. The phase morphology and surface and optoelectronic properties of NCs before and after ligand exchange were discussed in depth. It was found that pure tetragonal-phase structure CZTSe NCs with approximately 1.7-eV bandgap could be synthesized. The removal of large organic molecules on CZTSe NCs after ligand exchange by S(2-) decreased the resistivity. The bandgap of the films after ligand exchange by 550°C selenization was also decreased due to better crystallinity. For potential application in CZTSe solar cells, we constructed an energy level diagram to explain the mutual effect between the absorption layer and CdS layer. Using cyclic voltammetry (CV) measurement, we found that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of CZTSe films shifted down after ligand exchange. After energy level alignment at the CdS/CZTSe interface, a type I band alignment structure was more conveniently formed after ligand exchange. This structure acted as the barrier against injection electrons from ZnO to the CZTSe layer, and recombination would subsequently be depressed.

Wurtzite copper-zinc-tin sulfide as a superior counter electrode material for dye-sensitized solar cells.

Wurtzite and kesterite Cu2ZnSnS4 (CZTS) nanocrystals were employed as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Compared to kesterite CZTS, the wurtzite CZTS exhibited higher electrocatalytic activity for catalyzing reduction of iodide electrolyte and better conductivity. Accordingly, the DSSC with wurtzite CZTS CE generated higher power conversion efficiency (6.89%) than that of Pt (6.23%) and kesterite CZTS (4.89%) CEs.

Enhanced performance of dye-sensitized solar cells using solution-based in situ synthesis and fabrication of Cu2ZnSnSe4 nanocrystal counter electrode.

On the bright side: A solution-based strategy was developed for in situ synthesis and film deposition of Cu2ZnSnSe4 nanocrystal films (samples a-d). The obtained Cu2ZnSnSe4 nanocrystal films can be used as an effective counter-electrode (CE) material to replace Pt, and yield low-cost, high-efficiency dye-sensitized solar cells (DSSCs). The assembled solar cell devices exhibit an efficiency of 7.82 % under 1 sun irradiation (see figure).

Surfactant-free CuInS2 nanocrystals: an alternative counter-electrode material for dye-sensitized solar cells.

Surfactant-free CuInS2 (CIS) nanocrystals (NCs) were synthesized by replacing organic capping ligands with inorganic ions S(2-). The efficacy of ligand exchange was probed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis spectroscopy, and Fourier-transform infrared (FTIR). The surfactant-free CIS NCs films were obtained by drop-casting onto the clean FTO glass. The electrical conductivity and electrocatalytic activity of CIS NCs films were sharply increased due to the improved interparticle coupling after ligand exchange. When the surfactant-free CIS films were used as counter electrode (CE) in dye-sensitized solar cells (DSSCs), a conversion efficiency of η = 5.77% was achieved without sintering.

One-step synthesis of stoichiometric Cu2ZnSnSe4 as counter electrode for dye-sensitized solar cells.

Cu(2)ZnSnSe(4) (CZTSe) nanoparticles with diameters of 200-300 nm were synthesized by one-step solvothermal method without surfactants or templates. The structure, composition and morphology of CZTSe nanoparticles were characterized by XRD, XPS, Raman spectrum, EDS, FESEM and TEM. The results indicated that the nanoparticles were single phase and nearly stoichiometric composition. CZTSe nanoparticles drop-casted onto FTO substrate were used as counter electrode (CE) in dye-sensitized solar cells (DSSCs) for the first time, which exhibited Pt-like electrocatalytic activity for the reduction of I(3)(-) to I(-) in DSSCs. The J-V results demonstrated that the thickness of the film affected the photocurrent density and fill factor remarkably, which resulted from the difference of electrocatalytic sites and resistance with different thickness films. And a best efficiency of 3.85% was obtained by adjusting the film thickness. The work presents a new approach for developing low-cost, facile fabrication CZTSe nanoparticles, and demonstrates CZTSe can be explored as a low-cost alternative for expensive and scare Pt in DSSCs.

Effect of highly ordered single-crystalline TiO2 nanowire length on the photovoltaic performance of dye-sensitized solar cells.

One-dimensional semiconductor nanostructures grown directly onto transparent conducting oxide substrates with a high internal surface area are most desirable for high-efficiency dye-sensitized solar cells (DSSCs). Herein, we present a multicycle hydrothermal synthesis process to produce vertically aligned, single crystal rutile TiO(2) nanowires with different lengths between 1 and 8 µm for application as the working electrode in DSSCs. Optimum performance was obtained with a TiO(2) nanowire length of 2.0 µm, which may be ascribed to a smaller nanowire diameter with a high internal surface area and better optical transmittance with an increase in the incident light intensity on the N719 dye; as well as a firm connection at the FTO/TiO(2) nanowire interface.

Solution fabrication and photoelectrical properties of CuInS2 nanocrystals on TiO2 nanorod array.

One-dimensional semiconductor architectures are receiving attention in preparing photovoltaic solar cells because of its superior charge transport as well as excellent light-harvesting efficiency. In this study, vertically aligned single-crystalline TiO(2) nanorods array was grown directly on transparent conductive glass (FTO), and then CuInS(2) nanocrystals were deposited on nanorods array by spin coating method to form TiO(2)/CuInS(2) heterostructure films. The resulting nanostructure assembly and composition was confirmed by field-emission scanning electron microscope (FESEM) , transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction(XRD). Ultraviolet-visible absorption spectroscopy (UV-vis) data indicates that the absorbance of the nanocomposite film extended into the visible region compared with bare TiO(2) nanorod arrays. The surface photovoltage spectra (SPS) also showed a new and enhanced response region corresponding to the absorption spectrum. These results suggest that the novel CuInS(2) nanocrystals sensitized TiO(2) nanorod array on FTO photoelectrodes has a potential application in photovoltaic devices.

Molecularly imprinted polymer for selective extraction of domoic acid from seafood coupled with high-performance liquid chromatographic determination.

In this work, a highly selective sample cleanup procedure that combining molecular imprinting technique (MIT) and solid phase extraction (SPE) was developed for the isolation of domoic acid (a fascinating marine toxin) from seafood samples. The molecular imprinting polymer (MIP) for domoic acid was prepared using 1,3,5-pentanetricarboxylic acid as the template molecule instead of domoic acid. 4-Vinyl pyridine was used as the functional monomer and ethylene glycol dimethacrylate was used as the cross-linking monomer. The obtained imprinted polymer showed high affinity to domoic acid and was used as selective sorbent for the SPE of domoic acid from seafood samples. An off-line molecularly imprinted solid phase extraction (MISPE) method followed by high-performance liquid chromatography (HPLC) with diode-array detection for the detection of domoic acid was also established. Good linearity was obtained from 0.5 mg L(-1) to 25 mg L(-1) (R(2)>0.99) with a quantitation limit of 0.1 mg L(-1), which was sufficient to determine domoic acid at the maximum level permitted by several authorities. The mean recoveries of domoic acid from mussel extracts were 93.4-96.7%. It was demonstrated that the proposed MISPE-HPLC method could be applied to direct determination of domoic acid from seafood samples.

Synthesis and photoluminescence of a full zinc blende phase ZnO nanorod array.

A single-crystalline ZnO nanorod array with rectangular cross-sections has been synthesized, in which the as-obtained products are a complete metastable zinc blende (ZB) phase. X-ray powder diffraction, electron microscopy, and elemental maps have been used to show that the ZB-ZnO samples have a lattice constant a = 4.580 Å, and are free from contamination by hexagonal wurtzite (HW) ZnO. Based on our experimental data, the associated growth mechanism is tentatively suggested. In addition, the photoluminescence (PL) spectrum (about 400 nm (3.1 eV)) of the as-fabricated ZB-ZnO products was detected; this is the first experimental report of the optical properties of ZB-ZnO nanorod arrays.