PbS quantum dot based hybrid-organic photodetectors for X-ray sensing

• A novel hybrid-organic photodetector for the detection of X-rays was created.
• A photoactive oBHJ was produced by incorporating PbS quantum dots into an organic blend.
• The use of PbS in the oBHJ increased the X-ray stopping power of such devices, making them suitable as X-ray detectors.
• Rectification decreased with increasing device thickness.
• Thick devices behaved as photoconductors rather than as photodiodes.

Nanocomposites consisting of conductive polymers and functional nanoparticles have recently been employed in photodetectors and imagers. Here, we present a novel hybrid-organic photodetector (HPD) that was optimized for the detection of X-rays meeting the specific needs of medical imaging. Devices were fabricated using inorganic lead sulfide (PbS) nanocrystal (NC) quantum dots (QDs) and a blend of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Quantum dots convert X-rays directly into charge-carriers that then migrate through the organic blend to the contacting electrodes. The performance of such devices depends on the thickness and probably on the morphology of the active layer. We discuss the synthesis and characterization of the PbS quantum dots, their incorporation into a HPD, and the performance of the HPD in X-ray sensing. Scanning electron microscopy and transmission electron microscopy show the PbS-QD distribution in the organic matrix. We find a strong tendency of the QDs to phase-separate from the organic blend.

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