Electrical effects of metal nanoparticles embedded in ultra-thin colloidal quantum dot films

Plasmonic light trapping can increase the absorption of light in thin semiconductor films. We investigate the effect of embedded metal nanoparticle (MNP) arrays on the electrical characteristics of ultra-thin PbS colloidal quantum dot (CQD) photoconductors. We demonstrate that direct contact with the metalnanoparticles can suppress or enhance the photocurrent depending on the work function of the metal, which dominates the optical effects of the particles for ultra-thin films. These results have implications for designing plasmonic CQD optoelectronic devices.This research has been supported by Fundacio0 Privada Cellex Barcelona and the European Commission’s Seventh Framework Programme for Research under contract PIRG06-GA-2009-256355 and the Ministerio de Ciencia e Innovacion under Contract No. TEC2011-24744

Efficient Photon Recycling and Radiation Trapping in Cesium Lead Halide Perovskite Waveguides

Cesium lead halide perovskite materials have attracted considerable attention for potential applications in lasers, light-emitting diodes, and photodetectors. Here, we provide the experimental and theoretical evidence for photon recycling in CsPbBr3 perovskite microwires. Using two-photon excitation, we recorded photoluminescence (PL) lifetimes and emission spectra as a function of the lateral distance between PL excitation and collection positions along the microwire, with separations exceeding 100 μm. At longer separations, the PL spectrum develops a red-shifted emission peak accompanied by an appearance of well-resolved rise times in the PL kinetics. We developed quantitative modeling that accounts for bimolecular recombination and photon recycling within the microwire waveguide and is sufficient to account for the observed decay modifications. It relies on a high radiative efficiency in CsPbBr3 perovskite microwires and provides crucial information about the potential impact of photon recycling and waveguide trapping on optoelectronic properties of cesium lead halide perovskite materials

Enhanced optical path and electron diffusion length enable high-efficiency perovskite tandems

Tandem solar cells involving metal-halide perovskite subcells offer routes to power conversion efficiencies (PCEs) that exceed the single-junction limit; however, reported PCE values for tandems have so far lain below their potential due to inefficient photon harvesting. Here we increase the optical path length in perovskite films by preserving smooth morphology while increasing thickness using a method we term boosted solvent extraction. Carrier collection in these films – as made – is limited by an insufficient electron diffusion length; however, we further find that adding a Lewis base reduces the trap density and enhances the electron-diffusion length to 2.3 μm, enabling a 19% PCE for 1.63 eV semi-transparent perovskite cells having an average near-infrared transmittance of 85%. The perovskite top cell combined with solution-processed colloidal quantum dot:organic hybrid bottom cell leads to a PCE of 24%; while coupling the perovskite cell with a silicon bottom cell yields a PCE of 28.2%