Heavy-Metal-Free Solution-Processed Nanoparticle-Based Photodetectors: Doping of Intrinsic Vacancies Enables Engineering of Sensitivity and Speed

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Abstract
Photodetection in semiconductors enables digital imaging, spectroscopy, and optical communications. Integration of solution-processed light-sensing materials with a range of substrates offers access to new spectral regimes, the prospect of enhanced sensitivity, and compatibility with flexible electronics. Photoconductive photodetectors based on solution-cast nanocrystals have shown tremendous progress in recent years; however, high-performance reports to date have employed Pb- and Cd-containing materials. Here we report a high-sensitivity (photon-to-electron gain >40), high-speed (video-frame-rate-compatible) photoconductive photodetector based on In2S3. Only by decreasing the energetic depth of hole traps associated with intrinsic vacancies in beta-phase In2S3 were we able to achieve this needed combination of sensitivity and speed. Our incorporation of Cu+ cations into beta-In2S3’s spinel vacancies that led to acceptable temporal response in the devices showcases the practicality of incorporating dopants into nanoparticles. The devices are stable in air and under heating to 215 °C, advantages rooted in the reliance on the stable inclusion of dopants into available sites instead of surface oxide species.