Controlled anion mixing in halide perovskites has been shown to be an effective route to precisely tune optoelectronic properties in order to achieve efficient photovoltaic, light emission, and radiation detection devices. However, an atomistic understanding behind the precise mechanism impacting the performances of mixed halide perovskite devices, particularly as a radiation detector, is still missing. Combining high-level computational methods and multiple experiments, here we systematically investigate the effect of chlorine (Cl) incorporation on the optical and electronic properties, structural stability, ion migration, and the γ-ray radiation detection ability of MAPbBr3–x Cl x . We observe that precise halide mixing suppresses bromide ion migration and consequently reduces the dark current by close to a factor of two, which significantly increases the resistance of the mixed anion devices. Furthermore, reduced carrier effective masses and mostly unchanged exciton binding energies indicate enhanced charge carrier transport for these perovskite alloys. At the atomistic level, modifications to ion migration and charge carrier transport properties improve electronic properties and predominantly contribute to the better response and resolution in high-energy γ-ray detection with MAPbBr3–x Cl x as compared to MAPbBr3. This study provides a systematic approach to enhance the high-energy radiation detection ability of MAPbBr3–x Cl x -based devices by understanding the atomistic properties underpinning performance.

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Halide perovskites are promising optoelectronic semiconductors. For applications in solid-state detectors that operate in low photon flux counting mode, blocking interfaces are essential to minimize the dark current noise. Here, we investigate the interface between methylammonium lead tri-iodide (MAPbI 3 ) single crystals and commonly used high and low work function metals to achieve photon counting capabilities in a solid-state detector. Using scanning photocurrent microscopy, we observe a large Schottky barrier at the MAPbI 3 /Pb interface, which efficiently blocks dark current. Moreover, the shape of the photocurrent profile indicates that the MAPbI 3 single-crystal surface has a deep fermi level close to that of Au. Rationalized by first-principle calculations, we attribute this observation to the defects due to excess iodine on the surface underpinning emergence of deep band-edge states. The photocurrent decay profile yields a charge carrier diffusion length of 10−25 μm. Using this knowledge, we demonstrate a single-crystal MAPbI 3 detector that can count single γ-ray photons by producing sharp electrical pulses with a fast rise time of <2 μs. Our study indicates that the interface plays a crucial role in solid-state detectors operating in photon counting mode.

photo voltaics, perovskite solar cells have already exceeded 23% in power conversion efficiency in a short development period. [1][2][3][4] OMHPs have also become popular in many other optoelectronic applications, such as light-emitting diodes, [5,6] photodetectors, [7,8] and lasing applications. [9] Properties such as tunable band gaps, [10,11] low trap state densities, [12] and long carrier diffusion lengths make OMHPs a desirable material for a wide range of optoelectronic applications, as well as being a focus for other semiconducting device applications. [13,14] These fascinating optoelectronic properties have recently sparked a new interest for applications of OMHPs for high-energy radiation detectors, which are considered as a critical technology in many fields, including nuclear safeguards, nuclear forensics, and astrophysics. Notably, current solid-state detector technologies using classical semiconductors have many challenges that must be overcome for wide spread development. For example, Cadmium Zinc Telluride (CZT) is a commercial γ-ray detection semiconductor achieving reasonable resolution (≈2% at 662 keV) at room temperature. However, the complicated and costly high-quality crystal growth for this semiconductor fabrication prohibits its broad adaptation. Another example of a more cost-effective semiconductor is high purity Germanium, (HPGe) which achieves an impressive resolution, (≈0.2% at 662 keV) albeit under operation at liquid nitrogen temperatures. [15] Thus, achieving cost efficient, robust high resolution detection at ambient conditions has been a long-time aim for semiconductor γ-ray detectors. In this arena, lead-halide based perovskites have been proposed as a new generation semiconductors in γ -spectroscopy for its low-cost solution process and simple crystal growth for room temperature detectors. [16][17][18] The incorporation of high-Z elements (i.e., Pb) underscores the opportunity for enhanced photoelectric interaction probability. Large band gaps and high resistivities are also essential for highly sensitive operation in the resistive mode. [19] Moreover, the long carrier lifetime and decent ambipolar mobility give great potential for single photon counting and pulse mode radiation sensing. [15] Previous reports have shown promising proof-of-principle results for the application of perovskites as ionizing radiation In recent years, hybrid perovskite single crystalline solid-state detectors have shown promise in γ-ray spectroscopy. Here, the γ-ray photon induced electrical pulses are investigated, which are produced by perovskite solid-state detectors made with the commonly used methylammonium lead tribromide crystals with chlorine incorporation. Under low electric field detector operation, slow pulses generated by γ-rays with average rise times of 65 µs are observed, which decreases to 20 µs when a higher electrical field of 500 V cm −1 is applied. However, the baseline becomes noisy quickly, which prevents collection of clean pulses for spectra construction. Further, by systematic...

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