Heavy-metal-free solution-processed nanoparticle-based photodetectors: Doping of intrinsic vacancies enables engineering of sensitivity and speed

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 ln ₂S ₃. Only by decreasing the energetic depth of hole traps associated with intrinsic vacancies in beta-phase ln ₂S ₃ were we able to achieve this needed combination of sensitivity and speed. Our incorporation of Cu ⁺ cations into beta-ln ₂S ₃'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.