Hybrid photodiodes promise cost-effective short-wave IR imaging

A combination of organic and inorganic nanoscale materials, along with solution processing, enables a tunable imager for short-wave infrared imaging (SWIR). A ternary composite of electron- and hole-conducting organic semiconductor blended with the colloidal QDs yielded highly sensitive SWIR photodiodes. The diodes comprised a solution-processable photoactive absorber layer sandwiched between an indium tin oxide (ITO) anode covered by a poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) interlayer and a low work function cathode (Ca/Ag or Al). The doctor bladed absorber layer consisted of an hole conducting regioregular poly(3-hexylthiophene) (rr-P3HT), an electron conducting [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) and oleic acid capped PbS QDs as SWIR sensitizer. The devices achieved external quantum efficiencies (EQEs) of up to 51%. With glass-encapsulated hybrid diodes and operating at room temperature, the flat-panel imager is sensitive up to 1.9 μm.