Reduction of High Dark Currents in Organic SWIR Photodetectors Using Novel Solution-Processable Narrow Bandgap Donors

Near-infrared (NIR) and short-wave infrared (SWIR) light detection is critical for imaging in the biological window, motion sensing, and night vision cameras, among other applications, and demand for these sensors is rapidly expanding for low power devices to enable the internet of things. Silicon (Si)-based detectors are commonly used to detect light in the ultraviolet-visible to NIR region with wavelengths up to 1000nm beyond which silicon becomes less efficient or able to absorb incident photons. Germanium and indium gallium arsenide (InGaAs) are efficient absorbers in the SWIR region but are considered to be prohibitively costly for widespread adoption in large area and distributed sensing platforms and incompatible with flexible form factors. On the other hand, organic photodetectors (OPDs) are light weight, low cost, scalable and solution-processable which are advantageous for those same applications. However, SWIR OPDs are often less efficient than their inorganic counterparts and sensitive to midgap trap states and energetic disorder which can result in high reverse bias dark currents that limit detectivity.

In this work we have synthesized several [1,2,5]thiadiazolo[3,4-g]quinoxaline-based p-type donor polymers with tailored optical absorption peak wavelengths up to 1180nm and absorption onsets up to 1450nm that were then used to fabricate solution processed bulk heterojunction SWIR OPDs. These devices have exhibited EQE >10% in the SWIR region but initial dark currents were extremely high. Several adjustments to the device architecture including active layer refinements as well as the optimization of charge blocking layers and interfaces results in suppressed OPD dark currents. Further investigation of the devices’ response time, capacitance, and active layers morphological and spectroscopic characteristics elucidate trap and disorder-related properties that contribute to the high dark currents.