Hardness of PbS nanocrystal-based photoconductor to x-ray irradiation

Colloidal lead sulfide (PbS) nanocrystals (NCs) are emerging as cost-effective and solution-processable materials for infrared (IR) detection. Their use in a space environment is conditioned by their radiation tolerance. This study investigates the intrinsic robustness of PbS NC-based photoconductive devices to high-dose x-ray irradiation (up to 1.6 Grad [PbS]), far above the requirements for deep-space operation. PbS NC films exhibit gradual performance degradation without abrupt thresholds, attributed to their polycrystalline nature, which localizes defects and mitigates long-range lattice disruption. Optoelectronic measurements reveal a drop in both the dark and illuminated response, yet the signal-to-noise ratio improves due to the faster decay of the dark current. Spectroscopic analyses (x-ray photoemission spectroscopy/hard x-ray photoemission spectroscopy) confirm that the conductivity change can be attributed to x-ray-induced oxidation, which affects both Pb and S, forming sulfate and lead hydroxide phases that propagate throughout the NC volume. This oxidation reduces the effective NC size, blue-shifting the excitonic peak. Despite this, PbS NCs exhibit exceptional radiation hardness, comparable to that of radiation-hardened CMOS devices. These findings position PbS NCs as viable candidates for spaceborne IR detection, especially in oxygen-free environments where oxidation is naturally limited.