A tetrathienopyrrole-based ladder-type donor polymer for high-performance organic near-infrared cavity detectors

Abstract

Organic semiconductors can afford detection at wavelengths beyond commercial silicon photodetectors. However, for each targeted near-infrared wavelength range, this requires individually optimized materials, which adds to the complexity and costs. Moreover, finding molecules with strong absorption beyond 1 mu m that perform well in organic photodetectors remains a challenge. In microcavity devices, the detection window can be extended to wavelengths inaccessible for silicon without the need for new materials by adopting an intelligent design. Previous work has demonstrated the applicability of a dithienopyrrole-based donor polymer (PDTPQx) in such a cavity photodetector device, with a photoresponse up to 1200 nm. In this work, the pi-conjugated backbone of the polymer is extended, affording higher hole mobility and better donor:acceptor intermixing. This leads to enhanced peak external quantum efficiencies up to 1450 nm. The (thermal noise limited) detectivities achieved with the PTTPQx polymer (1.07 x 1012 to 1.82 x 1010 Jones) are among the very best in the 900-1400 nm wavelength regime. Ladder-type extension of a push-pull donor polymer affords enhanced peak external quantum efficiencies in microcavity organic photodetectors, with detectivities ranging from 1.07 x 1012 to 1.82 x 1010 Jones in the 900-1400 nm regime.