Meidan Ye

High Efficiency Dye-Sensitized Solar Cells Based on Hierarchically Structured Nanotubes

Dye-sensitized solar cells (DSSCs) based on hierarchically structured TiO(2) nanotubes prepared by a facile combination of two-step electrochemical anodization with a hydrothermal process exhibited remarkable performance. Vertically oriented, smooth TiO(2) nanotube arrays fabricated by a two-step anodic oxidation were subjected to hydrothermal treatment, thereby creating advantageous roughness on the TiO(2) nanotube surface (i.e., forming hierarchically structured nanotube arrays-nanoscopic tubes composed of a large number of nanoparticles on the surface) that led to an increased dye loading. Subsequently, these nanotubes were exploited to produce DSSCs in a backside illumination mode, yielding a significantly high power conversion efficiency, of 7.12%, which was further increased to 7.75% upon exposure to O(2) plasma.

Hierarchically structured nanotubes for highly efficient dye-sensitized solar cells.

Hierarchical TiO2 nanotube arrays grown on Ti foil are yielded by subjecting electrochemically anodized, vertically oriented TiO2 nanotube arrays to hydrothermal processing. The resulting DSSCs exhibit a significantly enhanced power conversion efficiency of 7.24%, which is a direct consequence of the synergy of higher dye loading, superior light-scattering ability, and fast electron transport.

Optimized porous rutile TiO2 nanorod arrays for enhancing the efficiency of dye-sensitized solar cells

Highly ordered rutile TiO2 nanorod arrays (NRAs) are promising architectures in dye-sensitized solar cells (DSCs). However, the efficiency of DSCs based on such photoanodes is still relatively low, largely due to the limited internal surface area. Herein, we report that highly oriented rutile TiO2 NRAs with film thickness up to ∼30 μm was developed by a facile hydrothermal method. More importantly, an optimized porous rutile TiO2 NRAs with a large internal surface area was fabricated on the FTO (fluorine-doped tin oxide) substrate via a secondary hydrothermal treatment and when applied as the photoanodes in DSCs, a record efficiency of 7.91% was achieved.

Recent advancements in perovskite solar cells: flexibility, stability and large scale

Recent progress in organic–inorganic halide perovskite solar cells (PSCs) has attracted great attention due to their impressive photovoltaic properties, and easy device manufacturing with facile layer deposition by solution processes, suggesting their great potential for large-scale applications. Remarkably, the power conversion efficiencies (PCEs) of PSCs have jumped from 3.8% of methyl ammonium lead halide, CH3NH3PbX3 (X = Br, I), sensitized liquid solar cells in 2009, to more than 20% of all solid-state solar cells in 2015. Just over the past 6 years, numerous efforts have contributed to promote PSCs with more attractive properties, in preparation for future commercial applications, such as high PCE, high stability, high flexibility, large area, low cost, environmental friendliness, etc. In this review, we will concentrate on the recent advancements in the aspects of flexibility, stability and large scale of PSCs. We strive to present a comprehensive overview and show a deep understanding of the reported strategies for PSC devices with flexible, stable and large-scale properties.

Plasmon‐Mediated Solar Energy Conversion via Photocatalysis in Noble Metal/Semiconductor Composites

Plasmonics has remained a prominent and growing field over the past several decades. The coupling of various chemical and photo phenomenon has sparked considerable interest in plasmon‐mediated photocatalysis. Given plasmonic photocatalysis has only been developed for a relatively short period, considerable progress has been made in improving the absorption across the full solar spectrum and the efficiency of photo‐generated charge carrier separation. With recent advances in fundamental (i.e., mechanisms) and experimental studies (i.e., the influence of size, geometry, surrounding dielectric field, etc.) on plasmon‐mediated photocatalysis, the rational design and synthesis of metal/semiconductor hybrid nanostructure photocatalysts has been realized. This review seeks to highlight the recent impressive developments in plasmon‐mediated photocatalytic mechanisms (i.e., Schottky junction, direct electron transfer, enhanced local electric field, plasmon resonant energy transfer, and scattering and heating effects), summarize a set of factors (i.e., size, geometry, dielectric environment, loading amount and composition of plasmonic metal, and nanostructure and properties of semiconductors) that largely affect plasmonic photocatalysis, and finally conclude with a perspective on future directions within this rich field of research.

In situ growth of CuS and Cu1.8S nanosheet arrays as efficient counter electrodes for quantum dot-sensitized solar cells

Vertical CuS nanosheet arrays were synthesized in situ for the first time on transparent conducting fluorine-doped tin oxide (FTO) substrates via a facile solvothermal process of seeded FTO glasses in the presence of ethanol solvent only containing thiourea and Cu(NO3)2 as a precursor. While choosing CuCl instead of Cu(NO3)2 as the copper precursor in the same solvothermal process, porous Cu1.8S nanosheets, for the first time, were also vertically grown on FTO substrates, suggesting that such a synthesis process is a general approach for the preparation of copper sulfide nanosheet arrays. When used as low-cost counter electrode materials in quantum dot-sensitized solar cells (QDSSCs), CuS (3.95%) and Cu1.8S (3.30%) nanosheet films exhibited enhanced power conversion efficiencies in comparison with the conventional Pt film (1.99%), which was primarily due to the excellent electrocatalytic activity of copper sulfides for the reduction of the polysulfide electrolyte used in CdSe/CdS QDSSCs. Significantly, the in situ growth strategy largely simplified the fabrication procedure of copper sulfide counter electrodes and, meanwhile, enhanced the adhesion between films and substrates.

One‐Dimensional Densely Aligned Perovskite‐Decorated Semiconductor Heterojunctions with Enhanced Photocatalytic Activity

By using one-dimensional rutile TiO(2) nanorod arrays as the structure-directing scaffold as well as the TiO(2) source to two consecutive hydrothermal reactions, densely aligned SrTiO(3) -modified rutile TiO(2) heterojunction photocatalysts are crafted for the first time. The first hydrothermal processing yielded nanostructured rutile TiO(2) with the hollow openings on the top of nanorods (i.e., partially etched rutile TiO(2) nanorod arrays; denoted PE-TNRAs). The subsequent second hydrothermal treatment in the presence of Sr(2+) transforms the surface of partially etched rutile TiO(2) nanorods into SrTiO(3) nanoparticles via the concurrent dissolution of TiO(2) and precipitation of SrTiO(3) while retaining the cylindrical shape (i.e., forming SrTiO(3) -decorated rutile TiO(2) composite nanorods; denoted STO-TNRAs). The structural and composition characterizations substantiate the success in achieving STO-TNRA nanostructures. In comparison to PE-TNRAs, STO-TNRA photocatalysts exhibit higher photocurrents and larger photocatalytic degradation rates of methylene blue (3.21 times over PE-TNRAs) under UV light illumination as a direct consequence of improved charge carrier mobility and enhanced electron/hole separation. Such 1D perovskite-decorated semiconductor nanoarrays are very attractive for optoelectronic applications in photovoltaics, photocatalytic hydrogen production, among other areas.

Hierarchically Structured Microspheres for High-Efficiency Rutile TiO2-Based Dye-Sensitized Solar Cells

Peachlike rutile TiO2 microsphere films were successfully produced on transparent conducting fluorine-doped tin oxide substrate via a facile, one-pot chemical bath route at low temperature (T = 80-85 °C) by introducing polyethylene glycol (PEG) as steric dispersant. The formation of TiO2 microspheres composed of nanoneedles was attributed to the acidic medium for the growth of 1D needle-shaped building blocks where the steric interaction of PEG reduced the aggregation of TiO2 nanoneedles and the Ostwald ripening process. Dye-sensitized solar cells (DSSCs) assembled by employing these complex rutile TiO2 microspheres as photoanodes exhibited a light-to-electricity conversion efficiency of 2.55%. It was further improved to a considerably high efficiency of 5.25% upon a series of post-treatments (i.e., calcination, TiCl4 treatment, and O2 plasma exposure) as a direct consequence of the well-crystallized TiO2 for fast electron transport, the enhanced capacity of dye loading, the effective light scattering, and trapping from microstructures.

Garden-like perovskite superstructures with enhanced photocatalytic activity

By subjecting amorphous flower-like TiO2 to a facile hydrothermal synthesis in the presence of Sr(2+), garden-like perovskite SrTiO3 superstructures were achieved. The amorphous TiO2 was preformed using ZnO flowers as templates. Different three-dimensional SrTiO3 architectures were coexisted in the garden, including SrTiO3 flowers composed of several hollow sword-shaped petals, many sheet-shaped petals or numerous flake-shaped petals, and SrTiO3 grass consisting of a number of long blades. These SrTiO3 superstructures were simultaneously grown on fluorine-doped tin oxide (FTO) substrates. On the basis of a comprehensive study on the effects of growth time, temperature, initial concentrations of precursor, and pH, the formation of these various hierarchical architectures was attributed primarily to the dissolution of amorphous TiO2 and precipitation of perovskite crystals, followed by the Ostwald ripening process of perovskite nanocrystals and self-organization of perovskite building blocks. Interestingly, this approach can be readily extended to create other perovskite structures, including dendritic BaTiO3 and nest-like CaTiO3, as well as PbTiO3 transformed from plate-like pyrochlore Pb2Ti2O6 after post-thermal treatment. Garden-like SrTiO3 superstructures showed a superior photocatalytic performance when compared to other as-prepared semiconductors and perovskite materials (i.e., ZnO, TiO2, BaTiO3, CaTiO3 and PbTiO3), probably due to their intrinsic photocatalytic activity and special garden-like features with a coexistence of various structures that significantly facilitated the adsorption and diffusion of methyl blue (MB) molecules and oxygen species in the photochemical reaction of MB degradation.

Interface engineering via an insulating polymer for highly efficient and environmentally stable perovskite solar cells

A tunnelling contact of polystyrene nanofilm was introduced for the first time at the interface of perovskite/hole transfer layer, leading to a significantly reduced charge recombination. Moreover, such a polymeric contact worked as a hydrophobic encapsulation layer for effectively protecting the perovskite against humidity. The resultant PSCs displayed a peak efficiency of 17.80% (vs. 15.90% of the control cell) and an enhanced stability.