Squaraine Dyes for Single‐Component Shortwave Infrared‐Sensitive Photodiodes and Upconversion Photodetectors

Abstract

Sensitive detection of shortwave infrared (SWIR) light using organic dyes will be a significant advance toward many applications in industry and research. Furthermore, from a fabrication and optimization view, photogeneration of charges in diodes consisting of a single dye layer will be highly attractive. However, SWIR dyes are scarce and organic photodiodes usually utilize a donor–acceptor materials combination to split excitons into charges. Here, it is demonstrated that single‐component layers of several SWIR squaraine dyes operate as efficient photodetectors, with peak external quantum efficiency > 40% beyond 1000 nm and sensitivity out to 1300 nm. Photocurrents show a superlinear dependence on reverse bias. It is shown that this results from a field‐assisted exciton dissociation mechanism, and not from field‐dependent charge injection or extraction. SWIR photodiodes are combined with organic light‐emitting diodes to fabricate upconversion photodetectors – devices that convert SWIR photons directly into visible light. Upconverters are characterized by a low turn‐on voltage (1.5 V) and a high luminance contrast (on‐off ratio 16 000) and SWIR‐to‐visible (λ = 575 nm) photon conversion efficiency (1.85%). Upconversion photodetectors emerge as a promising alternative to the current inorganic‐based imaging technology.