Abstract
A recent publication on single crystals of two-dimensional, layered organic–inorganic (BA)2CsAgBiBr7 double perovskite (BA+ = CH3CH23NH3+) suggested the great potential of this semiconductor material in the detection of X-ray radiation. Our powder XRD measurement confirms the crystallinity and purity of all samples that crystallise in the monoclinic space group P21/m, while the single crystal XRD measurements reveal the dominant {001} lattice planes. The structure–property relationship is reflected in the lower resistivity values determined from the van der Pauw measurements (1.65–9.16 × 1010 Ωcm) compared to those determined from the IV measurements (4.19 × 1011–2.67 × 1012 Ωcm). The density of trap states and charge-carrier mobilities, which are determined from the IV measurements, are 1.12–1.76 × 1011 cm–3 and 10−5–10−4 cm2V–1s–1, respectively. The X-ray photoresponse measurements indicate that the (BA)2CsAgBiBr7 samples synthesised in this study satisfy the requirements for radiation sensors. Further advances in crystal growth are required to reduce the density of defects and improve the performance of single crystals.
Highlights
X-ray security screening and medical diagnostic devices require radiation sensors with high resistivity ρ, enhanced charge-carrier mobility μ and collection efficiency to achieve higher sensitivity and lower detection limits
The inorganic, three-dimensional (3D) double perovskite Cs2AgBiBr6 radiation sensor is a stable substitute for the organic–inorganic lead-bearing perovskite MAPbBr3 [1,2,3,4,5,6] due to its higher moisture resistance, suppressed ion migration, absence of toxic lead, presence of heavier constituent elements and higher stopping power [7,8,9,10,11,12]
To further suppress ion migration in single crystals of Cs2AgBiBr6 and in turn increase ρ, their 3D structural dimensionality can be lowered to 2D dimensionality by incorporating
Summary
X-ray security screening and medical diagnostic devices require radiation sensors with high resistivity ρ, enhanced charge-carrier mobility μ and collection efficiency to achieve higher sensitivity and lower detection limits. Single crystal XRD measurements were performed using the Bruker D8 Discover diffractometer (MA, USA) This device features a high-resolution Cu-Kα radiation source (λ of 1.54060 Å Kα1 and λ of 1.54439 Å Kα2); a focusing Goebel mirror as the primary monochromator, including an 18 mm antiscatter slit and a 0.5 mm divergence slit in a fixed mode; and a line focus silicon-strip detector (LynxEye Xe). The evaluation of the ohmic behaviour of the Ag glue-(BA)2CsAgBiBr contacts (Figure S1a) from the IV characteristic curves, including the estimation of ρ, trap-filled limit voltage VTFL and μ and ntrap, was performed by applying the space charge limited current (SCLM) method [16,17,18,19,20,21,22,23]. The photocurrent values have estimated errors (relative) in the range of 2–5 %
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