41 research outputs found
Generalised Framework for Controlling and Understanding Ion Dynamics with Passivated Lead Halide Perovskites
Metal halide perovskite solar cells have gained widespread attention due to
their high efficiency and high defect tolerance. The absorbing perovskite layer
is as a mixed electron-ion conductor that supports high rates of ion and charge
transport at room temperature, but the migration of mobile defects can lead to
degradation pathways. We combine experimental observations and drift-diffusion
modelling to demonstrate a new framework to interpret surface photovoltage
(SPV) measurements in perovskite systems and mixed electronic ionic conductors
more generally. We conclude that the SPV in mixed electronic ionic conductors
can be understood in terms of the change in electric potential at the surface
associated with changes in the net charge within the semiconductor system. We
show that by modifying the interfaces of perovskite bilayers, we may control
defect migration behaviour throughout the perovskite bulk. Our new framework
for SPV has broad implications for developing strategies to improve the
stability of perovskite devices by controlling defect accumulation at
interfaces. More generally, in mixed electronic conductors our framework
provides new insights into the behaviour of mobile defects and their
interaction with photoinduced charges, which are foundational to physical
mechanisms in memristivity, logic, impedance, sensors and energy storage
Wonder tales of the ancient world,
Title-page in red and black within ornamental border.Mode of access: Internet
The sea-kings of Crete / by Rev. James Baikie, F.B.A.S. ; with 32 full-page illustrations from photographs.
Dual Mode Kelvin Probe: Featuring Ambient Pressure Photoemission Spectroscopy and Contact Potential Difference
AbstractWe describe a novel dual-mode Kelvin probe featuring ambient pressure Photoemission Spectroscopy (PES), which yields information on the absolute work function (Φ) of a metal and the Ionisation Potential (IP) of a semiconductor, coupled with a high resolution Contact Potential Difference capability which can be extended to Surface Photovoltage measurements. The relative energy resolution are 50 meV for PES and 1-3 meV for CPD. To surmount the limitation of electron scattering in air the incident photon energy is rastered rather than applying a variable retarding electric field as is used UPS. We propose a mechanism of atmospheric ion generation and show that for the metal photoresponse obeys Fowler Theory. The relationship between CPD and photoelectric threshold is a useful tool in characterizing the electrical behavior of materials. We illustrate this with native oxide covered Cu and n-type Si. Further we show that the photoresponse can be used to generate the near Fermi-level Density of States (DOS) in Iron and Nickel-Phthalocyanine