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  • Author(s):
    Prashant Kamat
    Abstract:

    Cesium lead halide perovskite films with a systematic change in the halide composition of CsPbBr3−xIx, in which iodide concentration varies from x = 0 to x = 3, provide a built-in gradient band structure. Such a gradient structure allows for the integrated capture of visible photons and directs them to the energetically low-lying iodide rich region. Annealing gradient halide perovskite films at temperatures ranging from 50 ○C to 90 ○C causes the films to homogenize into mixed halide perovskit…

    Date Published:
    2019-10
  • Author(s):
    Gergely Samu, Adam Balog, Filippo De Angelis, Daniele Meggiolaro, Prashant Kamat, Csaba Janáky
    Abstract:

    Abstract Halide ion mobility in metal halide perovskites remains an intriguing phenomenon, influencing their optical and photovoltaic properties. Selective injection of holes through electrochemical anodic bias has allowed us to probe the effect of hole trapping at iodide (0.9 V) and bromide (1.15 V) in mixed halide perovskite (CH3NH3PbBr1.5I1.5) films. Upon trapping holes at the iodide site, the iodide gradually gets expelled from the mixed halide film (as iodine and/or triiodide ion), leavi…

    Date Published:
    2019-06
  • Author(s):
    Ádám Balog, Gergely Samu, Prashant Kamat, Casba Janáky
    Abstract:

    Detailed mechanistic understanding of the optoelectronic features is a key factor in designing efficient and stable photoelectrodes. In situ spectroelectrochemical methods were employed to scrutinize the effect of trap states on the optical and electronic properties of CuI photoelectrodes and to assess their stability against (photo)electrochemical corrosion. The excitonic band in the absorption spectrum and the Raman spectral features were directly influenced by the applied bias potential. T…

    Date Published:
    2019-01
  • Author(s):
    Tor Elmelund, Rebecca Scheidt, Brian Seger, Prashant Kamat
    Abstract:

    MAPbBr3 and MAPbI3 films cast onto glass slides and physically paired together undergo halide exchange to form mixed halide films. The change in halide composition in these two ∼130 nm thick films occurs concurrently with Br− diffusing toward the MAPbI3 film and I− diffusing toward the MAPbBr3 film. The diffusion of these halide species, which is tracked through changes in the absorption, offers a direct measurement of thermally activated halide diffusion in perovskite films. The increase in …

    Date Published:
    2019-06
  • Author(s):
    Rebecca Scheidt, Corey Atwell, Prashant Kamat
    Abstract:

    The control of grain size and surface properties is an important parameter in controlling the optoelectronic and photovoltaic properties of metal halide perovskites. When CsPbBr 3 nanocrystal (∼10 nm in diameter) films were annealed at 100−125 °C, they grow in size to produce ∼400 nm diameter crystallites while transforming into bulk perovskite films. Characteristic changes in the optical properties were noted when such transformation occurred from nanocrystals into bulk. By tracking absorban…

    Date Published:
    2019-06
  • Author(s):
    Sarah Chapman, Prashant Kamat
    Abstract:

    The suppression of halide ion exchange between CsPbBr3 and CsPbI3 nanocrystals achieved through capping with PbSO4–oleate has enabled us to deposit different perovskite nanocrystals as aligned arrays on the electrode surfaces without intermixing of species. The electrophoretic deposition of PbSO4–oleate-capped CsPbX3 (X = Cl, Br, I) nanocrystals suspended in hexane solution on mesoscopic TiO2 films allows the design of controlled architecture with single or multiple layers of perovskite films…

    Date Published:
    2018