The widespread use of X- and gamma-rays in a range of sectors including healthcare, security and industrial screening is underpinned by the efficient detection of the ionising radiation. Such detector...
Photodetectors with multiple spectral response bands
have shown
promise to improve imaging and communications through the switchable
detection of different photon energies. However, demonstrations to
date have been limited to only two bands and lack capability for fast
switching in situ. Here, we exploit the band gap tunability and capability
of all-perovskite tandem solar cells to demonstrate a new device concept
realizing four spectral bands of response from a single multijunction
device, with fast, optically controlled switching between the bands.
The response to monochromatic light is highly selective and narrowband
without the need for additional filters and switches to broader response
bands on applying bias light. Sensitive photodetection above 6 ×
1011 Jones is demonstrated in all modes, with rapid switching
response times of <250 ns. We demonstrate proof of principle on
how the manipulation of the modular multiband detector response through
light conditions enables diverse applications in optical communications
with secure encryption.
Halide perovskites have shown promise to advance the field of light detection in next-generation photodetectors, offering performance and functionality beyond what is currently possible with traditional inorganic semiconductors. Despite a relatively high density of defects in perovskite thin films, long carrier diffusion lengths and lifetimes suggest that many defects are benign. However, perovskite photodetectors show detection behavior that varies with time, creating inconsistent device performance and difficulties in accurate characterization. Here, we link the changing behavior to mobile defects that migrate through perovskites, leading to detector currents that drift on the time scale of seconds. These effects not only complicate reproducible device performance but also introduce characterization challenges. We demonstrate that such transient phenomena generate measurement artifacts that mean the value of specific detectivity measured can vary by up to 2 orders of magnitude even in the same device. The presence of defects can lead to photoconductive gain in photodetectors, and we show batch-to-batch processing variations in perovskite devices gives varying degrees of charge carrier injection and photocurrent amplification under low light intensities. We utilize the passivating effect of aging to reduce the impact of defects, minimizing current drifts and eliminating the gain. This work highlights the potential issues arising from mobile defects, which lead to inconsistent photodetector operation, and identifies the potential for defects to tune photodetection behavior in perovskite photodetectors.
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