Considerable effort is being expended on the development of efficient silicon light-emitting devices compatible with silicon-based integrated circuit technology. Although several approaches are being explored, all presently suffer from low emission efficiencies, with values in the 0.01-0.1% range regarded as high. Here we report a large increase in silicon light-emitting diode power conversion efficiency to values above 1% near room temperature-close to the values of representative direct bandgap emitters of a little more than a decade ago. Our devices are based on normally weak one- and two-phonon assisted sub-bandgap light-emission processes. Their design takes advantage of the reciprocity between light absorption and emission by maximizing absorption at relevant sub-bandgap wavelengths while reducing the scope for parasitic non-radiative recombination within the diode. Each feature individually is shown to improve the emission efficiency by a factor of ten, which accounts for the improvement by a factor of one hundred on the efficiency of baseline devices.

Concerns over possible toxicities of conventional metal-containing quantum dots have inspired growing research interests in colloidal silicon nanocrystals (SiNCs), or silicon quantum dots (SiQDs). This is related to their potential applications in a number of fields such as solar cells, optoelectronic devices and fluorescent bio-labelling agents. The past decade has seen significant progress in the understanding of fundamental physics and surface properties of silicon nanocrystals. Such understanding is based on the advances in the preparation and characterization of surface passivated colloidal silicon nanocrystals. In this critical review, we summarize recent advances in the methods of preparing high quality silicon nanocrystals and strategies for forming self-assembled monolayers (SAMs), with a focus on their bio-applications. We highlight some of the major challenges that remain, as well as lessons learnt when working with silicon nanocrystals (239 references).

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In this paper we demonstrate the first use of enhanced optical forces and optically induced thermophoretic and convective forces produced by surface plasmon polariton excitation for large-scale ordering and trapping of colloidal aggregations. We identify regimes in which each of these forces dominate the colloidal dynamics and lead to different collective equilibrium states. These include accumulation and organization into hexagonal close-packed colloidal crystals, arrangement into linear colloidal particle chains, and the formation of colloids in a ring formation about the excited region.Peer ReviewedPostprint (published version

The last 4 years have seen the rapid emergence of a new solar cell technology based on organic-inorganic lead halide perovskites, primarily CH3NH3PbI3 and related halides involving Cl and Br. Debate continues on the role of excitons and free carriers in these materials. Recent studies report values of exciton binding energy for the iodide ranging from 0.7 meV to 200 meV, with vastly different implications for device operation and design. In the present work, previously neglected polarons are shown likely to have a major impact in determining excitonic properties. Polaronic exciton binding energies calculated using effective longitudinal optical phonon energies, deduced from permittivity measurements, are shown consistent with experimental energies for good quality samples of CH3NH3PbI3 and CH3NH3PbBr3, as determined over a large temperature range from optical absorption data. Bandgaps determined simultaneously show a discontinuity at the orthorhombic to tetragonal phase transition for the iodide, but not for the bromide.