X-rays are widely used in probing inside information nondestructively, enabling broad applications in the medical radiography and electronic industries. X-ray imaging based on emerging lead halide perovskite scintillators has received extensive attention recently. However, the strong self-absorption, relatively low light yield and lead toxicity of these perovskites restrict their practical applications. Here, we report a series of nontoxic double-perovskite scintillators of Cs 2 Ag 0.6 Na 0.4 In 1-y Bi y Cl 6. By controlling the content of the heavy atom Bi 3+ , the X-ray absorption coefficient, radiative emission efficiency, light yield and light decay were manipulated to maximise the scintillator performance. A light yield of up to 39,000 ± 7000 photons/MeV for Cs 2 Ag 0.6 Na 0.4 In 0.85 Bi 0.15 Cl 6 was obtained, which is much higher than that for the previously reported lead halide perovskite colloidal CsPbBr 3 (21,000 photons/MeV). The large Stokes shift between the radioluminescence (RL) and absorption spectra benefiting from self-trapped excitons (STEs) led to a negligible selfabsorption effect. Given the high light output and fast light decay of this scintillator, static X-ray imaging was attained under an extremely low dose of ∼1 μGy air , and dynamic X-ray imaging of finger bending without a ghosting effect was demonstrated under a low-dose rate of 47.2 μGy air s −1. After thermal treatment at 85°C for 50 h followed by X-ray irradiation for 50 h in ambient air, the scintillator performance in terms of the RL intensity and X-ray image quality remained almost unchanged. Our results shed light on exploring highly competitive scintillators beyond the scope of lead halide perovskites, not only for avoiding toxicity but also for better performance.

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The power conversion efficiency (PCE) of low-bandgap mixed Pb−Sn perovskite solar cells (PSCs) has been significantly hindered by large open-circuit voltage (V oc ) loss and poor fill factor (FF). Herein, mixed Pb−Sn perovskite films with a composition (FASnI 3 ) 0.6 (MAPbI 3 ) 0.4 were processed with a simple delayed annealing (DA) treatment that enables perovskite films with significantly reduced surface roughness. The treatment reduces nonradiative recombination of interfacial contacts when t h e p e r o v s k i t e fi l m s a r e i n t e r f a c e d w i t h p o l y ( 3 , 4ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) and fullerene (C 60 ). Charge transfer at the carrier-collection interfaces has been effectively improved, in agreement with time-resolved photoluminescence (TRPL) and transient photovoltage/photocurrent results. Consequently, the champion cell based on perovskite films with DA treatment shows a high V oc of 0.824 V, indicating a greatly suppressed V oc loss (for a bandgap of ∼1.25 eV), and an overall PCE of over 18.6%.

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