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

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.