Speaker
Description
Lead halide perovskite single crystals are promising for high-resolution photon-counting radiation detection due to their high atomic number and favourable charge-transport properties$^{[1]}$. However, most devices operate in hole-transport configurations, while currently existing application specific integrated circuits (ASICs) readout electronics are optimised for electron collection$^{[2]}$. Bridging this mismatch requires a clear understanding of carrier-polarity-dependent transport and the underlying device physics governing perovskite detectors.
We fabricate planar Schottky detectors based on formamidinium lead bromide (FAPbBr$_3$) perovskite single crystals with an Au/FAPbBr$_3$/Bi architecture. High-quality solution-grown FAPbBr$_3$ single crystals with X-ray rocking-curve linewidths as narrow as 0.0047° (16.9 arcsec) are used for detector fabrication. We investigate charge transport and stability of FAPbBr$_3$ planar detectors using α-particle ($^{241}$Am, 5.48 MeV) spectroscopy as a carrier-selective probe. By controlling the irradiation side and bias polarity, we isolate hole- and electron-transport signal formation and directly compare their spectroscopic response. Fresh devices exhibit superior hole transport, with energy resolution reaching 3.9% under α-particle excitation, whereas electron transport yields a broader energy resolution of 8.9%.
Upon continuous biasing (36 h at 5,000 V cm$^{-1}$) and shelf-life ageing (1 month), we observe pronounced polarity-dependent degradation. Hole signals collapse, accompanied by a substantial reduction in μτ (from 1.2 × 10$^{−3}$ cm$^{2}$ V$^{−1}$ to 5.2 × 10$^{−5}$ cm$^{2}$ V$^{−1}$) and the emergence of delayed pulse components, whereas electron transport shows only minor degradation, with μτ decreasing from 4.2 × 10$^{−4}$ to 2.6 × 10$^{−4}$ cm$^{2}$ V$^{−1}$.
Polarity-resolved α-particle measurements further reveal that degradation is strongly location-dependent. When carriers are generated near the Bi electrode, both hole and electron signals deteriorate after ageing, independent of bias polarity, indicating permanent degradation localised beneath the Bi contact. In contrast, analysis of the Au side via spatially resolved photoluminescence and time-resolved measurements (after electrode removal) shows a defect-rich interfacial region with enhanced non-radiative recombination.
These results demonstrate that charge transport in FAPbBr$_3$ detectors is primarily governed by metal/perovskite interfacial processes rather than intrinsic bulk properties. The observed asymmetry between electron and hole transport originates from localised interfacial defect formation, which selectively limits carrier extraction depending on the generation site.
Introduction of ultrathin interfacial layers (e.g., Ti or Cr) mitigates these effects, enabling stable hole- and electron-transport operation. Detectors remain stable after ~100 h of continuous biasing at 5,000 V cm$^{-1}$ and ~3 months of shelf-life storage.
The combination of high-quality crystals and interfacial protection layers enables the detectors to achieve 1.3% energy resolution for 662 keV ($^{137}$Cs γ-ray source) and 6.1% for 5.48 MeV α-particles in an electron-transport configuration. This work establishes interfacial degradation as the dominant performance-limiting factor in perovskite radiation detectors and identifies interfacial engineering as the key pathway toward stable, high-resolution hole- and electron-transport spectroscopy, providing a pathway toward compatibility with photon-counting ASIC architectures.
References
1. He, Y., Hadar, I. & Kanatzidis, M. G. Nat. Photon. 16, 1–13 (2022).
2. Mirzaei, A., Huh, J.-S., Kim, S. S. & Kim, H. W. Electron. Mater. Lett. 14, 261–287 (2018).