Enhanced light absorption and charge recombination control in quantum dot sensitized solar cells using tin doped cadmium sulfide quantum dots.

The photovoltaic performance of quantum dot sensitized solar cells (QDSSCs) is limited due to charge recombination processes at the photoelectrode/electrolyte interfaces. We analyzed the effect of Sn4+ ion incorporation into CdS quantum dots (QDs) deposited onto TiO2 substrates in terms of enhancing light absorption and retarding electron-hole recombination at the TiO2/QDs/electrolyte interfaces. Sensitization involved depositing CdS QDs with different Sn4+ concentrations on the surface of TiO2 using a facile and cost-effective successive ionic layer adsorption and reaction (SILAR) method. Optimized photovoltaic performance of Sn-CdS sensitized QDSSCs was explored using CuS counter electrodes (CEs) and a polysulfide electrolyte. Structural and optical studies of the photoanodes revealed that the gaps between CdS nanoparticles were partially filled by Sn4+ ions, which enhanced the light absorption of the solar cell device. Electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD) tests suggested that Sn4+ ions can remarkably retard electron-hole recombination at the interfaces, stimulate electron injection into semiconductor QD layers, and provide long-term electron lifetime to the cells. We found that solar cells based on CdS photoanodes doped with 10% Sn4+ ions exhibited a superior power conversion efficiency (PCE) of 3.22%, open circuit voltage (Voc) of 0.593 V, fill factor (FF) of 0.561, and short-circuit current density (Jsc) of 9.68 mA cm-2 under an air mass coefficient (AM) 1.5 G full sun illumination. These values were much higher than those of QDSSCs based on bare CdS photoanodes (PCE = 2.16%, Voc = 0.552 V, FF = 0.471, and Jsc = 8.31 mA cm-2).

A cabbage leaf like nanostructure of a NiS@ZnS composite on Ni foam with excellent electrochemical performance for supercapacitors.

In the present study, a NiS@ZnS composite nanostructure was synthesized on a nickel foam substrate by a facile chemical bath deposition (CBD) method. The prepared composites were analyzed by X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and field emission scanning electron microscopy. The electrochemical performance of the supercapacitor (SC) electrodes was examined by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The NiS@ZnS composite exhibited a cabbage leaf like nanostructure and showed outstanding electrochemical performance in SCs with a specific capacitance of 1533.0 F g-1 at a current density of 7.5 A g-1, good cycling stability with 97.9% retention over 3000 cycles, greater energy density, and excellent rate capability compared to the bare NiS (1279.83 F g-1) and ZnS (616.66 F g-1)-based electrodes in SCs. The facile, novel synthesis method, outstanding performance, well defined surface morphology, synergetic effect and low cost make the NiS@ZnS composite an ideal electrode material for electrochemical energy storage devices.

Blue and blue-green light-emitting cationic iridium complexes: synthesis, characterization, and optoelectronic properties.

Two new cationic iridium complexes, [Ir(ppy)2(phpzpy)]PF6 (complex 1) and [Ir(dfppy)2(phpzpy)]PF6 (complex 2), bearing a 2-(3-phenyl-1H-pyrazol-1-yl)pyridine (phpzpy) ancillary ligand and either 2-phenylpyridine (Hppy) or 2-(2,4-difluorophenyl)pyridine (Hdfppy) cyclometalating ligands, were synthesized and fully characterized. The photophysical and electrochemical properties of these complexes were investigated by means of UV-visible spectroscopy, emission spectroscopy, and cyclic voltammetry. Density functional theory (DFT) and time dependent DFT (TD-DFT) calculations were performed to simulate and study the photophysical and electrochemical properties of both complexes. Light-emitting electrochemical cells (LECs) were fabricated by incorporating complexes 1 and 2, which respectively exhibit blue-green (488 and 516 nm) and blue (463 and 491 nm) emission colors, achieved through the meticulous design of the ancillary ligand. The luminance and current efficiency measurements recorded for the LEC based on complex 1 were 1246 cd m(-2) and 0.46 cd A(-1), respectively, and were higher than those measured for complex 2 because of the superior balanced carrier injection and recombination properties of the former.

Constructive effects of long alkyl chains on the electroluminescent properties of cationic iridium complex-based light-emitting electrochemical cells.

A series of cationic iridium complexes (1-6) were synthesized using alkylated imidazole-based ancillary ligands, and the photophysical and electrochemical properties of these complexes were subsequently evaluated. Light-emitting electrochemical cells (LECs) were fabricated from these complexes, and the effects of the alkyl chain length on the electroluminescent properties of the devices were investigated. The LECs based on these complexes resulted in yellow emission (complexes 1, 3, and 5) and green emission (complexes 2, 4, and 6) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.49, 0.50) and (0.33, 0.59), respectively. Our results indicate that the luminance and efficiency of the LECs can consistently be enhanced by increasing the alkyl chain length of the iridium complexes as a result of suppressed intermolecular interaction and self-quenching. Subsequently, a high luminance of 7309 cd m(-2) and current efficiency of 3.85 cd A(-1) were achieved for the LECs based on complex 5.