Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of "bottom-up" growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.

Bright light-emitting diodes based on solution-processable organometal halide perovskite nanoplatelets are demonstrated. The nanoplatelets created using a facile one-pot synthesis exhibit narrow-band emissions at 529 nm and quantum yield up to 85%. Using these nanoparticles as emitters, efficient electroluminescence is achieved with a brightness of 10 590 cd m(-2) . These ligand-capped nanoplatelets appear to be quite stable in moisture, allowing out-of-glovebox device fabrication.

Semiconductor nanowires are promising for photovoltaic applications, but, so far, nanowire-based solar cells have had lower efficiencies than planar cells made from the same materials, even allowing for the generally lower light absorption of nanowires. It is not clear, therefore, if the benefits of the nanowire structure, including better charge collection and transport and the possibility of enhanced absorption through light trapping, can outweigh the reductions in performance caused by recombination at the surface of the nanowires and at p-n junctions. Here, we fabricate core-shell nanowire solar cells with open-circuit voltage and fill factor values superior to those reported for equivalent planar cells, and an energy conversion efficiency of ∼5.4%, which is comparable to that of equivalent planar cells despite low light absorption levels. The device is made using a low-temperature solution-based cation exchange reaction that creates a heteroepitaxial junction between a single-crystalline CdS core and single-crystalline Cu2S shell. We integrate multiple cells on single nanowires in both series and parallel configurations for high output voltages and currents, respectively. The ability to produce efficient nanowire-based solar cells with a solution-based process and Earth-abundant elements could significantly reduce fabrication costs relative to existing high-temperature bulk material approaches.

Highly bright light-emitting diodes based on solution-processed all-inorganic perovskite thin film are demonstrated. The cesium lead bromide (CsPbBr ) created using a new poly(ethylene oxide)-additive spin-coating method exhibits photoluminescence quantum yield up to 60% and excellent uniformity of electrical current distribution. Using the smooth CsPbBr films as emitting layers, green perovskite-based light-emitting diodes (PeLEDs) exhibit electroluminescent brightness and efficiency above 53 000 cd m and 4%: a new benchmark of device performance for all-inorganic PeLEDs.

Photocatalytic water splitting represents a promising way to produce renewable hydrogen fuel from solar energy. Ultrathin semiconductor electrodes for water splitting are of particular interest because the optical absorption occurs in the region where photogenerated charge carriers can effectively contribute to the chemical reactions on the surface. It is therefore important to manipulate and concentrate the incident light so that more photons can be absorbed within the thin film. Here we show an enhanced photocurrent in a thin-film iron oxide photoanode coated on arrays of Au nanopillars. The enhancement can be attributed primarily to the increased optical absorption originating from both surface plasmon resonances and photonic-mode light trapping in the nanostructured topography. The resonances can be tuned to a desirable wavelength by varying the thickness of the iron oxide layer. A net enhancement as high as 50% was observed over the solar spectrum.

Printed organometal halide perovskite light-emitting diodes (LEDs) are reported that have indium tin oxide (ITO) or carbon nanotubes (CNTs) as the transparent anode, a printed composite film consisting of methylammonium lead tribromide (Br-Pero) and poly(ethylene oxide) (PEO) as the emissive layer, and printed silver nanowires as the cathode. The fabrication can be carried out in ambient air without humidity control. The devices on ITO/glass have a low turn-on voltage of 2.6 V, a maximum luminance intensity of 21014 cd m(-2), and a maximum external quantum efficiency (EQE) of 1.1%, surpassing previous reported perovskite LEDs. The devices on CNTs/polymer were able to be strained to 5 mm radius of curvature without affecting device properties.

The functionality and performance of a semiconductor is determined by its bandgap. Alloying, as for instance in InxGa1-xN, has been a mainstream strategy for tuning the bandgap. Keeping the semiconductor alloys in the miscibility gap (being homogeneous), however, is non-trivial. This challenge is now being extended to halide perovskites – an emerging class of photovoltaic materials. While the bandgap can be conveniently tuned by mixing different halogen ions, as in CsPb(BrxI1-x)3, the so-called mixed-halide perovskites suffer from severe phase separation under illumination. Here, we discover that such phase separation can be highly suppressed by embedding nanocrystals of mixed-halide perovskites in an endotaxial matrix. The tuned bandgap remains remarkably stable under extremely intensive illumination. The agreement between the experiments and a nucleation model suggests that the size of the nanocrystals and the host-guest interfaces are critical for the photo-stability. The stabilized bandgap will be essential for the development of perovskite-based optoelectronics, such as tandem solar cells and full-color LEDs.

This paper provides direct evidence for the role of surface plasmons in the enhanced optical transmission of light through metallic nanoscale hole arrays. Near-field optical images directly confirmed the presence of surface plasmons on gold nanohole arrays with interhole spacings larger than the surface plasmon wavelength. A simple interference model provides an intuitive explanation of the two types of fringe wavelengths observed in the near-field optical images. Far-field spectroscopy revealed a surface plasmon band that contributed a factor >8 to the transmission enhancement. Furthermore, silicon nanohole arrays did not exhibit any features in the near-field, which demonstrates that metallic materials are necessary for enhanced light transmission through nanohole arrays.Ground-breaking discoveries in diverse fields such as photonics, 1-5 chemistry, 6,7 and biophysics 8,9 have relied on surface plasmon polaritons (SPPs) to confine and enhance light in the optical near-field. Interest in the fundamental science of SPPs was revived in part by the report of extraordinary light transmission through metallic subwavelength hole arrays 1 which did not follow classical optical theory. 10 SPPs were initially proposed to assist in this enhanced transmission, 11 although subsequent theoretical and experimental work has claimed different mechanisms. [12][13][14] Understanding the role of SPPs in enhanced transmission is crucial for exploiting its nature to beat diffraction in applications such as subwavelength optics and nanophotonics. Here we present direct evidence for SPP-mediated enhanced transmission through gold nanohole arrays by combining, for the first time, near-field and far-field measurements of films with interhole spacings larger than the SPP wavelength. We propose a simple model that explains two types of interference in the near-field patterns and measure an SPP-enhancement factor > 8 in our gold hole arrays.Surface plasmon polaritons are collective charge oscillations that are produced by the resonant interaction between light and free electrons at the interface of metallic and dielectric materials. Additional momentum is required to couple light into SPPs because of their different dispersion relations. 15 This condition is typically satisfied by a corrugated surface such as a grating or by evanescent coupling with a prism or a near-field probe. 15,16 Far-field spectroscopy has been the main approach for investigating enhanced transmission through subwavelength hole arrays; 17,18 however, far-field measurements cannot unambiguously identify the presence of SPPs since their electromagnetic field is trapped in the near-field region of the metal-dielectric interface. Near-field scanning optical microscopy (NSOM) is one technique that can directly image SPPs on a metal surface. In this Letter, we have combined NSOM imaging and far-field spectroscopy on isolated nanoholes and nanohole arrays in gold films to address the question of SPPenhanced optical transmission.Free-standing films of gold perforate...