Once the devices are exposed to the x-ray source, the 2D RP device shows a giant increase in x-ray–induced current density ( J X) at zero bias (short circuit), four orders of magnitude higher than dark current ( Fig.
cm by the forward-injection regime (fig.Note that the material’s intrinsic dark resistivity is calculated to be 5 × 10 12 ohm cm coming from the diode because of the efficient dark current blocking layers.Benefitting from the p- i- n junction design, the dark current density for the 2D RP device is as low as 10 −9 A cm −2 at zero bias and 10 −7 A cm −2 at −1 V, which translates to a high dark resistivity of 10 12 ohm 1D are used to describe the devices’ responses. The current density–voltage characteristics ( J-V) in the dark and under x-ray exposure as plotted in Fig. As a reference, we have also measured the commercial silicon p- i- n diode (600 μm thick) under the same condition.
The 2D RP x-ray absorber layers are fabricated with hot casting approach ( 14– 16) that formed a highly crystalline thin film to achieve enhanced charge transport and collection across the two electrodes ( 17).įigure 1 (D to F) summarizes the detector’s performance made with the 470-nm 2D RP thin film when measuring in the dark and under synchrotron beam with a mono energy of 10.91 keV and a photon flux of 2.7 × 10 12 photon counts per square centimeter per second (Ct cm −2 s −1) (x-ray photon flux calibration is described in Materials and Methods). S1), we then test the thin-film p- i- n detector under x-ray. Taking advantage of such strong x-ray absorption at perovskite materials (fig. Note that the μ l for both 2D and 3D perovskites are similar this suggests that the presence of the large organics in the 2D perovskites does not affect the x-ray absorption coefficients, which are dominated by the heavy elements. The absorption coefficient of these perovskite materials is, on average, 10- to 40-fold higher than that of silicon for hard x-ray. To evaluate the feasibility of perovskites as a radiation detector, we calculate linear x-ray absorption coefficient (μ l) as a function of incident energy (details can be found in Materials and Methods) for our 2D RPs, 3D methylammonium lead tri-iodide perovskite (MAPbI 3), and silicon (Si) and plot them in Fig. 1B further confirms the superior crystalline and preferred orientation in the 2D RP thin film ( 13, 14). The synchrotron grazing incidence wide-angle x-ray scattering (GIWAXS) measurement shown in Fig. 1A, the device uses a structure of indium tin oxide (ITO)/p-type contact/2D RP thin film/n-type contact/gold, where we chose poly (PTAA) as p-type contact and C 60 as n-type contact. Here, we design a new type of thin-film device made in p- i- n junction configuration with two-dimensional (2D) Ruddlesden-Popper (RP) phase layered perovskite (BA) 2(MA) 2Pb 3I 10 (Pb3) ( Fig. However, such a detector needs a high operational voltage across a large thickness (~1 cm), which has issues like charge drifting under or high fabrication cost for obtaining large volumes of monocrystals that undermine their use in scalable imaging application. Currently, this is attained using high-purity semiconducting single crystals ( 11) operating under high voltages across active regions ( 12) to efficiently collect generated charges and avoid recombination losses. Furthermore, the semiconducting materials used for detector need to be robust, without current drifting or current-voltage hysteresis. This will require (i) high-purity semiconductors to suppress thermally activated recombination in the dark via trap states and (ii) fully depleted junctions across active regions to avoid space charge accumulation and interfacial charge recombination. In a high-performance x-ray detector, one of the critical requirements is to minimize the dark current amplitude at reverse bias so that current generated at low x-ray dosage can be well resolved above the dark noise, which determines the device detectivity (i.e., the lowest detectable dosage). Solid-state radiation detectors directly convert x-ray signal into electrical current with superior sensitivity and high count rate that outperform other detection technologies and are critically needed in medical ( 1– 4) and security applications ( 5– 7) as well as in Advanced Photon Source facilities ( 8– 10).
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