Man-Jong Lee

Halide perovskite single crystals are promising active materials for direct x‐ray detectors because of their strong x‐ray absorption, efficient charge transport, and solution‐processable crystal growth. However, in thick single‐crystal detectors, lateral side surfaces can act as conductive leakage pathways, increasing dark current, inducing baseline drift, and generating transient overshoot and undershoot during x‐ray irradiation. Previous passivation and heterojunction strategies have mainly focused on metal–semiconductor interfaces, leaving side‐surface transport pathways insufficiently controlled. Here, a selective side‐surface ion‐exchange strategy is developed to construct halide‐gradient sidewall heterojunctions in MAPbBr ₃ single crystals. Through methylammonium chloride‐induced ion exchange, compositionally graded MAPbBr _{3 − x} Cl _x /MAPbBr ₃ multi‐heterojunctions are formed along the crystal sidewalls, creating wide‐bandgap lateral barriers that confine charge carriers within the Br‐rich bulk region. Spatial conductivity mapping and current‐distribution simulations reveal that the graded sidewalls suppress edge‐dominated conductivity and homogenize vertical charge transport without requiring guard‐ring electrodes. Consequently, side‐surface leakage, baseline drift, and transient undershoot are strongly suppressed, yielding reproducible and distortion‐free x‐ray responses. The treated detectors exhibit a 4.7‐fold enhancement in sensitivity, a 2.85‐fold reduction in detection limit, and markedly improved low‐dose x‐ray imaging contrast. This work establishes sidewall‐selective halide‐gradient engineering as a scalable route for lateral charge confinement in perovskite single‐crystal radiation detectors.

Perovskite solar cells (PSCs) offer a compelling route to developing lightweight, high‐specific‐power photovoltaic systems suitable for space applications. However, their durability in proton‐rich environments, typical of low‐Earth orbit, remains the key uncertainty that limits their deployment. In this study, we established how proton energy and fluence jointly determine the degradation thresholds in PSCs and showed that non‐ionizing energy loss dominates non‐recoverable degradation. By integrating controlled proton exposures with ion‐transport simulations, we identified energy‐dependent regimes in which atomic displacements drive A‐/X‐site depletion and lattice disorder, resulting in performance collapse beyond the critical accumulated dose. Under proton irradiation, a distinct mechanistic fingerprint was observed: the surface metallic Pb ⁰ diminished with increasing dose, in contrast to the accumulation of Pb ⁰ observed under photon irradiation. This finding supports a displacement‐dominated pathway. Finally, we demonstrated parylene‐C encapsulation that mitigates damage, and we defined a practical shielding criterion: effective protection requires a polymer thickness that exceeds the proton penetration depth corresponding to the energy spectrum of a given mission. These results provide both a unified framework for understanding proton–matter interactions in PSCs and for formulating actionable design rules for radiation‐hardened, lightweight solar modules capable of extended operation in space.

A diagnostic X-ray detector based on a perovskite single crystal (PSC) is demonstrated by introducing a carbon black-doped poly(3-hexylthiophene) (P3HT:CB) interlayer at the anode interface, exhibiting stable operation at high bias voltages and high sensitivity (>1.05 × 10⁶ μC Gy_air^-1 cm^-2). CB doping improves the stability of P3HT against oxidation and modulates interfacial potential, resulting in a hole-blocking barrier that reduces dark current and noise fluctuations under high electric fields. This is associated with improved detector stability, increasing ion migration activation energy from 0.069 to 0.191 eV and reducing effective trap density from 2.04 × 10¹¹ to 2.91 × 10⁹ cm^-3. The detector exhibits a stable baseline at high voltages (up to 200 V) and achieves an ultralow detection limit of 18.44 nGy s^-1. These results suggest the potential of interfacial potential modulation to enhance PSC-based detectors for X-ray detection and radiological imaging.

MAPbBr ₃ single crystals (MPB SCs) are promising materials for X‐ray detection; however, their use in low‐dose imaging is limited by high dark current, low detectability, and noise that degrades image clarity. Under X‐ray irradiation, where electron–hole pair generation is inherently low, suppressing defects is critical to minimize losses and maximize charge collection. In this study, metastable zone engineering is employed by tuning the MABr:PbBr ₂ ratio during inverse temperature crystallization (ITC) to produce defect‐suppressed MPB SCs. Excess MABr broadens and stabilizes the metastable zone, reducing nucleation events and enabling the growth of large, high‐crystallinity MPB SCs exceeding 10 mm within 11 h. These crystals exhibit electronic properties closer to intrinsic behavior, with prolonged carrier lifetimes of 371 ns and an enhanced mobility‐lifetime ( µτ ) product of 3.43 × 10 ⁻³ cm ² V ⁻¹ . Photoluminescence spectra reveal a distinct secondary peak from photon recycling, with intensity 1.25 times greater than the band‐edge peak, indicating efficient photon reabsorption due to reduced non‐radiative losses. Devices fabricated from excess MPB SCs achieve a record‐low detection limit of 0.47 nGy s ⁻¹ , high sensitivity (6.117 × 10 ³ µC Gy _air ⁻¹ cm ⁻² ), and high‐resolution X‐ray imaging, demonstrating strong potential for advanced medical and industrial applications.

The effect of low‐dose gamma‐ray irradiation on an amorphous SnO ₂ electron‐selective layer (ESL) was investigated in this study. Further, its impact on the photovoltaic (PV) performance of planar perovskite solar cells (PSCs) based on MAPbI ₃ and CsFAMAPbIBr absorber layers has been evaluated for the first time. The properties of the SnO ₂ layer were substantially modified by the gamma‐ray irradiation of regulatory exemption radioactive sources (Co‐60). Gamma‐ray irradiation promoted the formation of large perovskite grains by creating a hydrophilic surface via the generation of ─OH on the amorphous SnO ₂ film surface. In addition, gamma‐ray irradiation increased the conductivity of the SnO ₂ layer due to the generation of the proper oxygen vacancies in SnO ₂ . From the optimization of gamma‐ray irradiation parameters, we achieved a best efficiency of 18.03% using the MAPbI ₃ perovskite film owing to the enhanced perovskite densification and increased SnO ₂ conductivity. This efficiency was significantly improved compared to that (16.03%) of a pristine device. In addition, a power conversion efficiency (PCE) of 20.01% was achieved using the CsFAMAPbIBr mixed perovskite film and the gamma‐ray irradiated SnO ₂ . The results suggest that systematic low‐dose gamma irradiation treatment of ESLs has a synergistic effect of controlling surface properties, enhancing perovskite crystal growth, and controlling oxygen vacancies, and is relatively simple and has high potential as a surface treatment process.

Halide perovskite single crystals (SCs) have attracted much attention for their application in high‐performance x‐ray detectors owing to their desirable properties, including low defect density, high mobility–lifetime product (μτ), and long carrier diffusion length. However, suppressing the inherent defects in perovskites and overcoming the ion migration primarily caused by these defects remains a challenge. This study proposes a facile process for dipping Cs_0.05FA_0.9MA_0.05PbI₃ SCs synthesized by a solution‐based inverse temperature crystallization method into a 2‐phenylethylammonium iodide (PEAI) solution to reduce the number of defects, inhibit ion migration, and increase x‐ray sensitivity. Compared to conventional spin coating, this simple dipping process forms a two‐dimensional PEA₂PbI₄ layer on all SC surfaces without further treatment, effectively passivating all surfaces of the inherently defective SCs and minimizing ion migration. As a result, the PEAI‐treated perovskite SC‐based x‐ray detector achieves a record x‐ray sensitivity of 1.3 × 10⁵ μC Gy_air⁻¹ cm⁻² with a bias voltage of 30 V at realistic clinical dose rates of 1–5 mGy s⁻¹ (peak potential of 110 kVp), which is 6 times more sensitive than an untreated SC‐based detector and 3 orders of magnitude more sensitive than a commercial α‐Se‐based detector. Furthermore, the PEAI‐treated‐perovskite SC‐based x‐ray detector exhibits a low detection limit (73 nGy s⁻¹), improved x‐ray response, and clear x‐ray images by a scanning method, highlighting the effectiveness of the PEAI dipping approach for fabricating next‐generation x‐ray detectors. image