Record 1-micron thick QD film photodetectors using intercalated graphene electrodes for high responsivity in the infrared

Quantum dots (QDs) have extraordinary strong light absorption and size tunable bandgap. However, QD films are typically limited to ~200-300 nm due to their poor charge mobility. This severely limits the quantum efficiency of QD devices for λ <750 nm (infrared). Herein, we report a record 1 μm thick QD film using intercalated graphene layers as transparent current extractors. This overcomes QD poor mobility, ensuring both effective light absorption and charge extraction towards the near-infrared reaching quantum efficiency (EQE) of 90%. The short diffusion length (LD<200 nm) of QDs limits their useful thickness to ~200-300 nm1–4 , resulting in poor infrared light absorption. To overcome this limitation, we have built a 1 µm thick QD film with intercalated transparent graphene electrodes that keep high charge collection efficiency. As a result, the 1 µm intercalated devices show a superior EQE reaching 90% at λ ~800 nm without the drop of quantum efficiency at λ ~700 nm observed in most QD devices. The EQE of intercalated devices improves over the entire λ~ 600-1100 nm spectrum as the thickness increases from 100 nm to 1 μm, clearly breaking the restriction that the diffusion length of QDs imposes on the film thickness. This improves absorption and charge collection in the infrared.