In-situ fabrication of macroporous films for dye-sensitised solar cells: formation of the scattering layer and the gelation of electrolytes

Nanoarchitectures in dye-sensitized solar cells: metal oxides, oxide perovskites and carbon-based materials

Dye-sensitized solar cells (DSSCs) have aroused great interest and been regarded as a potential renewable energy resource among the third-generation solar cell technologies to fulfill the 21^st century global energy demand. DSSCs have notable advantages such as low cost, easy fabrication process and being eco-friendly in nature. The progress of DSSCs over the last 20 years has been nearly constant due to some limitations, like poor long-term stability, narrow absorption spectrum, charge carrier transportation and collection losses and poor charge transfer mechanism for regeneration of dye molecules. The main challenge for the scientific community is to improve the performance of DSSCs by using different approaches, like finding new electrode materials with suitable nanoarchitectures, dyes in composition with promising semiconductors and metal quantum dot fluorescent dyes, and cost-effective hole transporting materials (HTMs). This review focuses on DSSC photo-physics, which includes charge separation, effective transportation, collection and recombination processes. Different nanostructured materials, including metal oxides, oxide perovskites and carbon-based composites, have been studied for photoanodes, and counter electrodes, which are crucial to achieve DSSC devices with higher efficiency and better stability.

Broadband Light Absorption and Efficient Charge Separation Using a Light Scattering Layer with Mixed Cavities for High-Performance Perovskite Photovoltaic Cells with Stability

CH₃ NH₃ PbI₃ is one of the promising light sensitizers for perovskite photovoltaic cells, but a thick layer is required to enhance light absorption in the long-wavelength regime ranging from PbI₂ absorption edge (500 nm) to its optical band-gap edge (780 nm) in visible light. Meanwhile, the thick perovskite layer suppresses visible-light absorption in the short wavelengths below 500 nm and charge extraction capability of electron-hole pairs produced upon light absorption. Herein, we find that a new light scattering layer with the mixed cavities of sizes in 100 and 200 nm between transparent fluorine-doped tin oxide and mesoporous titanium dioxide electron transport layer enables full absorption of short-wavelength photons (λ < 500 nm) to the perovskite along with enhanced absorption of long-wavelength photons (500 nm < λ < 780 nm). Moreover, the light-driven electric field is proven to allow efficient charge extraction upon light absorption, thereby leading to the increased photocurrent density as well as the fill factor prompted by the slow recombination rate. Additionally, the photocurrent density of the cell with a light scattering layer of mixed cavities is stabilized due to suppressed charge accumulation. Consequently, this work provides a new route to realize broadband light harvesting of visible light for high-performance perovskite photovoltaic cells.

Synergistic effect of sunlight induced photothermal conversion and H2O2 release based on hybridized tungsten oxide gel for cancer inhibition

A highly efficient photochromic hydrogel was successfully fabricated via casting precursor, which is based on amorphous tungsten oxide and poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide). Under simulated solar illumination, the hydrogel has a rapid and controlled temperature increasing ratio as its coloration degree. Localized electrons in the amorphous tungsten oxide play a vital role in absorption over a broad range of wavelengths from 400 nm to 1100 nm, encompassing the entire visible light and infrared regions in the solar spectrum. More importantly, the material exhibits sustainable released H2O2 induced by localized electrons, which has a synergistic effect with the rapid surface temperature increase. The amount of H2O2 released by each film can be tuned by the light irradiation, and the film coloration can indicate the degree of oxidative stress. The ability of the H2O2-releasing gels in vitro study was investigated to induce apoptosis in melanoma tumor cells and NIH 3T3 fibroblasts. The in vivo experimental results indicate that these gels have a greater healing effect than the control in the early stages of tumor formation.

Broadband and Low-Loss Plasmonic Light Trapping in Dye-Sensitized Solar Cells Using Micrometer-Scale Rodlike and Spherical Core-Shell Plasmonic Particles

Dielectric scattering particles have widely been used as embedded scattering elements in dye-sensitized solar cells (DSCs) to improve the optical absorption of the device. Here we systematically study rodlike and spherical core-shell silica@Ag particles as more effective alternatives to the dielectric scattering particles. The wavelength-scale silica@Ag particles with sufficiently thin Ag shell support hybrid plasmonic-photonic resonance modes that have low parasitic absorption losses and a broadband optical response. Both of these features lead to their successful deployment in light trapping in high-efficiency DSCs. Optimized rodlike silica@Ag@silica particles improve the power conversion efficiency of a DSC from 6.33 to 8.91%. The dimension, surface morphology, and concentration of these particles are optimized to achieve maximal efficiency enhancement. The rodlike silica particles are prepared in a simple one-pot synthesis process and then are coated with Ag in a liquid-phase deposition process by reducing an Ag salt. The aspect ratio of silica rods is tuned by adjusting the temperature and duration of the growth process, whereas the morphology of Ag shell is tailored by controlling the reduction rate of Ag salt, where slower reduction in a polyol process gives a smoother Ag shell. Using optical calculations, the superior performance of the plasmonic core-shell particles is related to the large number of hybrid photonic-plasmonic resonance modes that they support.

Designing nanobowl arrays of mesoporous TiO₂ as an alternative electron transporting layer for carbon cathode-based perovskite solar cells

In this work, we have designed a mesoporous TiO2 nanobowl (NB) array with pore size, bowl size and film thickness being easily controllable by the sol-gel process and the polystyrene (PS) template diameter. Based on the TiO2 NB array, we fabricated carbon cathode based perovskite solar cells (C-PSCs) to investigate the impact of TiO2 NB nanostructures on the performance of the as-obtained C-PSCs devices. As expected, the TiO2 NB based devices show a higher power conversion efficiency (PCE) than that of the planar counterpart, mainly due to the enhanced light absorption arising from the NB-assisted light management, the improved pore-filling of high quality perovskite crystals and the increased interface contact for rapid electron extraction and fast charge transport. Leveraging these advantages of the novel TiO2 NB film, the 220 nm-PS templated TiO2 NB based devices performed the best on both light absorption capability and charge extraction, and achieved a PCE up to 12.02% with good stability, which is 37% higher than that of the planar counterpart. These results point to a viable and convenient route toward the fabrication of TiO2 ETL nanostructures for high performance PSCs.

Photonic design of embedded dielectric scatterers for dye sensitized solar cells

A photonic design approach is proposed to determine the optimal size and concentration of dielectric scatterers for nanostructured solar cells.