Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.324
Publication date: 18th July 2019
Thanks to their high X-ray absorption coefficient and good charge carriers transport properties, hybrid (organic-inorganic) halogenoplumbate perovskites exhibit interesting properties for direct X-ray detection. Among the different perovskite compositions, CH3NH3PbBr3 could be a promising candidate for solution-process, low-cost and large-area flat-panel X-ray detector.
In this work, monocrystalline CH3NH3PbBr3 perovskite crystals were prepared by using the inverse temperature crystallisation (ITC) method using dimethylformamide (DMF) as solvent. Symmetric contacts were deposited by evaporation of chromium or brushing of PEDOT-PSS in opposite side of the singles crystals, and the dark current and X-ray induced photocurrent were compared.
Dark current-voltage characteristic (J-V curves) were carried out at room temperature, by sweeping the voltage at low scan rates of 200 mV.s-1. Resistivity measurements indicate values around 108 Ω.cm. Symmetrical contacts would entail symmetric J-V curves. However, devices with PEDOT-PSS electrodes show non-symmetric J-V curves with large hysteresis and high temporal variations. On the other hand, devices with chromium contacts show symmetric J-V curves without hysteresis and with reduced temporal variations.
The samples were irradiated by X-ray using medical radiography settings (70 kV, 23.5 mm of aluminum filtering, dose rate: 100 µGyair/s, 100 ms per shot with 4 Hz repetition rate). The X-ray to electron conversion rate was measured with respect to the applied voltage. Devices with PEDOT-PSS electrodes present a photocurrent with large rise time and fall time, along with photoconduction gain which depends on the device voltage history. By comparison, devices with chromium contacts have lower conversion rate without gain, associated with shorter rise time and fall time.
The non-stable behaviour of devices with PEDOT-PSS contacts will results in undesired temporal artefacts such as ghosting in dynamic X-ray imaging such as angiography. The devices with chromium contacts will be preferable for this application.
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