Fabrication of heterostructure multilayer devices through the optimization of Bi-metal sulfides for high-performance quantum dot-sensitized solar cells

In this work, a titanium dioxide and lead sulfide (TiO2/PbS) nano-size heterostructure with tin sulfide was fabricated and coated via a two-step direct deposition process. Its microstructure, morphology, elemental composition, optical absorption, and photochemical activity were investigated. Linear sweep voltammetry and cyclic voltammetry curves substantiated its catalytic activity, indicating quantum dot effects of a well-developed space charge domain on the surface of the hybrid structure. These give rise to electron-hole recombination suppression and a high charge mobility rate. Moreover, direct stabilization was identified in current density, corresponding to the hybrid structures limiting the diffusion current process. Higher J SC values observed were substantiated by the role of quantum dot-size effects and enhanced crystalline structures, leading to a reduction in series resistance and an improved conversion efficiency of 10.05%. Overall, theoretical analyses and empirical findings indicated that the seamless migration of photoexcited electrons across the interfaces of SnS and PbS is linked to quantum dot effect synergy. This is facilitated by the space charge region, which serves as a conduit for efficient electron transfer between the respective materials.

Unveiling a Counterintuitive Intermode Interplay in a Prototype Plasmonic Nanosystem

We demonstrate a counterintuitive intermode interplay in the plasmonic system of gold nanorods, i.e., energy transfer (EnT) from the lower-energy longitudinal (L) mode to the higher-energy transverse (T) mode. The opening of this EnT(L→T) channel is enabled by an energy upconversion process with the L mode, in which the solvent environment plays a critical role. Switching from a strong thermal-conductivity solvent (i.e., water) to a much weaker one (i.e., chloroform) brings on prolongation of plasmonic hot-electron lifetime and enhancement of phonon emission, thereby increasing the probability of L-mode energy upconversion assisted by self-absorption of phonon emission. The pertinent justification and further manipulation of EnT(L→T) are provided by control experiments mainly from ultrafast spectroscopy. Besides, a subtle intermode dynamic screening effect in this unary plasmonic system is also addressed. This work refreshes our knowledge about the elusive intermode interplay in plasmonic systems and offers implementable strategies to harness hot electrons toward plasmon-mediated applications.

Tin Sulfide (SnS) Films Deposited by an Electric Field-Assisted Continuous Spray Pyrolysis Technique with Application as Counter Electrodes in Dye-Sensitized Solar Cells

The deposition of tin sulfide (SnS) nanostructured films using a continuous spray pyrolysis technique is reported with an electric field present at the nozzle for influencing the atomization and the subsequent film deposition. In the absence of the electric field, the X-ray diffraction pattern shows the orthorhombic phase of SnS with a crystallographic preferred orientation along the (040) plane. The application of the electric field results in significant improvement in the morphology and a reduction in surface roughness (28 nm from 37 nm). The direct optical band gap of the films deposited with and without the electric field is estimated to be 1.5 and 1.7 eV, respectively. The photothermal deflection spectroscopy studies show a lower energetic disorder (no Urbach tail), which indicates an annealing effect in the SnS films deposited under the electric field. The improvement in the film properties is reflected in the expected improvement in the power conversion efficiency (PCE) of dye-sensitized solar cells fabricated using the SnS film as a counter electrode. An enhancement of PCE from 2.07% for the film deposited without the electric field to 2.89% for the film deposited with the electric field shows the role of the electric field in the fabrication of improved SnS films.

A Photoelectrochemical Study of Hybrid Organic and Donor—Acceptor Dyes as Sensitizers for Dye-Sensitized Solar Cells

An investigation on the photoelectrochemical and sensitizing properties of two different hybrid organic dyes, anchored as sensitizers on mesoporous TiO2, in Grätzel solar cells, is presented. Firstly, we studied the absorption properties of the C106 sensitizer, a Ru polypyridine complex, and of the Y123, an organic push and pull dye. In this work, we characterized these two dyes, employing two different electrolytes, with similar experimental condition and device parameters. From the J–V curves and IPCE photo action spectra, we performed an inedited bifacial study based on the comparison of their photovoltaic performances, exploiting several backgrounds (black or white). Among the obtained results from this study, we found the best bifaciality factor of 93% for C106 and the best power conversion efficiency of 12.8% for Y123. These results represent, concerning these two dyes and to the best of our knowledge, some of the highest values in literature.

Plasmonic dye-sensitized solar cells through collapsible gold nanofingers

Plasmonic nanostructures are successfully demonstrated in solar cells due to their broad spectra-selective resonance in the range of ultraviolet to near-infrared, and thus light absorption can be mostly improved and power conversion efficiency (PCE) further. Here, we demonstrate plasmonic dye-sensitized solar cells (DSSCs) using collapsible Au nanofingers to build photoanode to enhance light absorption. In this plasmonic DSSCs, by balancing local field enhancement due to gap-plasmon resonance and dye fluorescence quenching, the optimal gap size in collapsed Au/Al₂O₃/Au nanofingers is designed by twice the Al₂O₃thickness and then deposited a TiO₂layer as photoanode. The results show that the PCE of DSSCs is mostly improved as compared to DSSCs with photoanode of Au/Al₂O₃/TiO₂films, which can be ascribed to the coupled local field enhancement within the sub-nanometer gaps. In addition, fluorescence of dyes on plasmonic nanofingers is nearly 10 times higher than plain Au/Al₂O₃/TiO₂films, which further proves the dye absorption enhancement. These plasmonic nanofingers enable the precise engineering of gap-plasmon modes and can be scaled up to wafer scale with low cost by the nanoimprint lithography technique, which suggests the feasibility of applying our result in constructing the photoanode for other types of solar cells.

Enhanced photovoltaic properties of dye-sensitized solar cells using three-component CNF/TiO2/Au heterostructure

To further increase the photoelectric efficiency of dye-sensitized solar cell (DSSC), enhancing the light adsorption of photoanode and suppressing the recombination of photo-generated charges are of great importance. Motivated by this, a novel and efficient three-component CNF/TiO₂/Au heterostructure was successfully constructed and employed as an alternative photoanode material. The as-prepared CNF/TiO₂/Au is characterized by conductive carbon nanofiber (CNF) core, uniform TiO₂ outer shell assembled by upright nanorods, and surface modification with well-dispersed Au nanoparticles. To demonstrate the potential application of such material in DSSC, a comparison of photoelectric properties with commercial P25 and binary composite CNF/TiO₂ was carried out. By contrast, the ternary composite CNF/TiO₂/Au exhibited the highest short-circuit photocurrent density of 15.47 mA cm^-2 and photoelectric conversion efficiency of 6.45%, which is about 31% higher than that of the commercial P25-based DSSCs. The great improvement of photoelectric properties for ternary composite CNF/TiO₂/Au might be attributed to not only the conspicuous light adsorption ability derived from the sufficient dye loading of CNF/TiO₂/Au and the surface plasmon resonance of Au nanoparticles, but also the reduced recombination endowed by the conductive CNF core and the heterojunctions at the interface.