Xiangnan Dang

Virus-templated self-assembled single-walled carbon nanotubes for highly efficient electron collection in photovoltaic devices

The performance of photovoltaic devices could be improved by using rationally designed nanocomposites with high electron mobility to efficiently collect photo-generated electrons. Single-walled carbon nanotubes exhibit very high electron mobility, but the incorporation of such nanotubes into nanocomposites to create efficient photovoltaic devices is challenging. Here, we report the synthesis of single-walled carbon nanotube-TiO(2) nanocrystal core-shell nanocomposites using a genetically engineered M13 virus as a template. By using the nanocomposites as photoanodes in dye-sensitized solar cells, we demonstrate that even small fractions of nanotubes improve the power conversion efficiency by increasing the electron collection efficiency. We also show that both the electronic type and degree of bundling of the nanotubes in the nanotube/TiO(2) complex are critical factors in determining device performance. With our approach, we achieve a power conversion efficiency in the dye-sensitized solar cells of 10.6%.

Highly Efficient Plasmon-Enhanced Dye-Sensitized Solar Cells through Metal@Oxide Core–Shell Nanostructure

We have investigated the effects of localized surface plasmons (LSPs) on the performance of dye-sensitized solar cells (DSSCs). The LSPs from Ag nanoparticles (NPs) increase the absorption of the dye molecules, allowing us to decrease the thickness of photoanodes, which improves electron collection and device performance. The plasmon-enhanced DSSCs became feasible through incorporating core-shell Ag@TiO(2) NPs into conventional TiO(2) photoanodes. The thin shell keeps the photoelectrons from recombining on the surface of metal NPs with dye and electrolyte and improves the stability of metal NPs. With 0.6 wt % Ag@TiO(2) NPs, the power conversion efficiency of DSSCs with thin photoanodes (1.5 μm) increases from 3.1% to 4.4%. Moreover, a small amount of Ag@TiO(2) NPs (0.1 wt %) improves efficiency from 7.8% to 9.0% while decreasing photoanode thickness by 25% for improved electron collection. In addition, plasmon-enhanced DSSCs require 62% less material to maintain the same efficiency as conventional DSSCs.

Tunable localized surface plasmon-enabled broadband light harvesting enhancement for high-efficiency panchromatic dye- sensitized solar cells

In photovoltaic devices, light harvesting (LH) and carrier collection have opposite relations with the thickness of the photoactive layer, which imposes a fundamental compromise for the power conversion efficiency (PCE). Unbalanced LH at different wavelengths further reduces the achievable PCE. Here, we report a novel approach to broadband balanced LH and panchromatic solar energy conversion using multiple-core-shell structured oxide-metal-oxide plasmonic nanoparticles. These nanoparticles feature tunable localized surface plasmon resonance frequencies and the required thermal stability during device fabrication. By simply blending the plasmonic nanoparticles with available photoactive materials, the broadband LH of practical photovoltaic devices can be significantly enhanced. We demonstrate a panchromatic dye-sensitized solar cell with an increased PCE from 8.3% to 10.8%, mainly through plasmon-enhanced photoabsorption in the otherwise less harvested region of solar spectrum. This general and simple strategy also highlights easy fabrication, and may benefit solar cells using other photoabsorbers or other types of solar-harvesting devices.

Biotemplated Synthesis of Perovskite Nanomaterials for Solar Energy Conversion

A synthetic method of using genetically engineered M13 virus to mineralize perovskite nanomaterials, particularly strontium titanate (STO) and bismuth ferrite (BFO), is presented. Genetically engineered viruses provide effective templates for perovskite nanomaterials. The virus-templated nanocrystals are small in size, highly crystalline, and show photocatalytic and photovoltaic properties.

Versatile Three-Dimensional Virus-Based Template for Dye-Sensitized Solar Cells with Improved Electron Transport and Light Harvesting

By genetically encoding affinity for inorganic materials into the capsid proteins of the M13 bacteriophage, the virus can act as a template for the synthesis of nanomaterial composites for use in various device applications. Herein, the M13 bacteriophage is employed to build a multifunctional and three-dimensional scaffold capable of improving both electron collection and light harvesting in dye-sensitized solar cells (DSSCs). This has been accomplished by binding gold nanoparticles (AuNPs) to the virus proteins and encapsulating the AuNP-virus complexes in TiO2 to produce a plasmon-enhanced and nanowire (NW)-based photoanode. The NW morphology exhibits an improved electron diffusion length compared to traditional nanoparticle-based DSSCs, and the AuNPs increase the light absorption of the dye-molecules through the phenomenon of localized surface plasmon resonance. Consequently, we report a virus-templated and plasmon-enhanced DSSC with an efficiency of 8.46%, which is achieved through optimizing both the NW morphology and the concentration of AuNPs loaded into the solar cells. In addition, we propose a theoretical model that predicts the experimentally observed trends of plasmon enhancement.

Tailoring metal halide perovskites through metal substitution: influence on photovoltaic and material properties

We present herein an experimental screening study that assesses how partially replacing Pb in methylammonium lead triiodide perovskite films with nine different alternative, divalent metal species, B′ = {Co, Cu, Fe, Mg, Mn, Ni, Sn, Sr, and Zn}, influences photovoltaic performance and optical properties. Our findings indicate the perovskite film is tolerant to most of the considered homovalent metal species with lead–cobalt compositions yielding the highest power conversion efficiencies when less than 6% of the Pb2+ ions are replaced. Through subsequent materials characterisation, we demonstrate for the first time that partially substituting Pb2+ at the B-sites of the perovskite lattice is not restricted to Group IV elements but is also possible with at least Co2+. Moreover, adjusting the molar ratio of Pb:Co in the mixed-metal perovskite affords new opportunities to tailor the material properties while maintaining stabilised device efficiencies above 16% in optimised solar cells. Specifically, crystallographic analysis reveals that Co2+ incorporates into the perovskite lattice and increasing its concentration can mediate a crystal structure transition from the cubic to tetragonal phase at room-temperature. Likewise, Co2+ substitution continually modifies the perovskite work function and band edge energies without either changing the band gap or electronically doping the intrinsic material. By leveraging this orthogonal dimension of electronic tunability, we achieve remarkably high open-circuit voltages up to 1.08 V with an inverted device architecture by shifting the perovskite into a more favourable energetic alignment with the PEDOT:PSS hole transport material.

Layer-by-layer assembled fluorescent probes in the second near-infrared window for systemic delivery and detection of ovarian cancer

Significance Survival of cancer patients can be greatly improved by an ideal theranostic platform capable of early detection and effective treatment of tumors. Layer-by-layer (LbL) assembly is a well-established technology and matches the requirement of modularity and versatility for such a theranostic platform. Second near-infrared window (NIR-II) fluorescence imaging is a promising modality with high resolution, deep penetration, and diminished noise. This work, for the first time to our knowledge, establishes a modular and versatile LbL platform for NIR-II agents and presents a head-to-head in vivo comparison of available NIR-II probes. We successfully achieve the selective, noninvasive, and safe detection of high-grade serous ovarian tumors in an orthotopic murine model. These LbL NIR-II probes promise the development of an NIR-II based theranostic platform of disease diagnosis, progression, and treatment. Fluorescence imaging in the second near-infrared window (NIR-II, 1,000–1,700 nm) features deep tissue penetration, reduced tissue scattering, and diminishing tissue autofluorescence. Here, NIR-II fluorescent probes, including down-conversion nanoparticles, quantum dots, single-walled carbon nanotubes, and organic dyes, are constructed into biocompatible nanoparticles using the layer-by-layer (LbL) platform due to its modular and versatile nature. The LbL platform has previously been demonstrated to enable incorporation of diagnostic agents, drugs, and nucleic acids such as siRNA while providing enhanced blood plasma half-life and tumor targeting. This work carries out head-to-head comparisons of currently available NIR-II probes with identical LbL coatings with regard to their biodistribution, pharmacokinetics, and toxicities. Overall, rare-earth-based down-conversion nanoparticles demonstrate optimal biological and optical performance and are evaluated as a diagnostic probe for high-grade serous ovarian cancer, typically diagnosed at late stage. Successful detection of orthotopic ovarian tumors is achieved by in vivo NIR-II imaging and confirmed by ex vivo microscopic imaging. Collectively, these results indicate that LbL-based NIR-II probes can serve as a promising theranostic platform to effectively and noninvasively monitor the progression and treatment of serous ovarian cancer.

Environmentally responsible fabrication of efficient perovskite solar cells from recycled car batteries

Organolead halide perovskite solar cells (PSCs) show great promise as a new large-scale and cost-competitive photovoltaic technology. Power conversion efficiencies over 15% to 19% have been achieved within 18 to 24 months of development, and thus perovskite materials have attracted great attention in photovoltaic research. However, the manufacture of PSCs raises environmental concerns regarding the over-production of raw lead ore, which has harmful health and ecological effects. Herein, we report an environmentally responsible process to fabricate efficient PSCs by reusing car batteries to simultaneously avoid the disposal of toxic battery materials and provide alternative, readily available lead sources for PSCs. Perovskite films, assembled using materials sourced from either recycled battery materials or high-purity commercial reagents, show the same material characteristics (i.e., crystallinity, morphology, optical absorption, and photoluminescence properties) and identical photovoltaic performance (i.e., photovoltaic parameters and resistances of electron recombination), indicating the practical feasibility of recycling car batteries for lead-based PSCs.

Graphene sheets stabilized on genetically engineered M13 viral templates as conducting frameworks for hybrid energy-storage materials.

Utilization of the material-specific peptide-substrate interactions of M13 virus broadens colloidal stability window of graphene. The homogeneous distribution of graphene is maintained in weak acids and increased ionic strengths by complexing with virus. This graphene/virus conducting template is utilized in the synthesis of energy-storage materials to increase the conductivity of the composite electrode. Successful formation of the hybrid biological template is demonstrated by the mineralization of bismuth oxyfluoride as a cathode material for lithium-ion batteries, with increased loading and improved electronic conductivity.

Layer-by-layer assembled porous photoanodes for efficient electron collection in dye-sensitized solar cells

Layer-by-layer (LbL) assembly is a versatile approach to generate hybrid materials with unique properties. Here, LbL is employed to insert genetically engineered M13 bacteriophage nanowires into a porous polymeric network for efficient dye-sensitized solar cell (DSSC) photoanodes. Both dip and spray LbL processes can be utilized in fabricating novel porous titanium dioxide (TiO2) photoanodes that exhibit advantageous electron transport properties, characterized by a longer electron diffusion length compared to the nanoparticle DSSC. Incorporation of the high aspect-ratio M13 bacteriophage, which yields electron percolation pathway and facilitates electron diffusion within the photoanode, is shown to further enhance the efficiency and the diffusion length in DSSCs.