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  1. Abstract

    To achieve high detectivity in infrared detectors, it is critical to reduce the device noise. However, for non-crystalline semiconductors, an essential framework is missing to understand and predict the effects of disorder on the dark current. This report presents experimental and modeling studies on the noise current in exemplar organic bulk heterojunction photodiodes, with 10 donor–acceptor combinations spanning wavelength between 800 and 1600 nm. A significant reduction of the noise and higher detectivity were found in devices using non-fullerene acceptors (NFAs) in comparison to those using fullerene derivatives. The low noise in NFA blends was attributed to a sharp drop off in the distribution of bandtail states, as revealed by variable-temperature density-of-states measurements. Taking disorder into account, we developed a general physical model to explain the dependence of thermal noise on the effective bandgap and bandtail spread. The model provides theoretical targets for the maximum detectivity that can be obtained at different detection wavelengths in inherently disordered infrared photodiodes.

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  2. Abstract

    This work examines an additive approach that increases dielectric screening to overcome performance challenges in organic shortwave infrared (SWIR) photodiodes. The role of the high‐permittivity additive, camphoric anhydride, in the exciton dissociation and charge collection processes is revealed through measurements of transient photoconductivity and electrochemical impedance. Dielectric screening reduces the exciton binding energy to increase exciton dissociation efficiency and lowers trap‐assisted recombination loss, in the absence of any morphological changes for two polymer variants. In the best devices, the peak internal quantum efficiency at 1100 nm is increased up to 66%, and the photoresponse extends to 1400 nm. The SWIR photodiodes are integrated into a 4 × 4 pixel imager to demonstrate tissue differentiation and estimate the fat‐to‐muscle ratio through noninvasive spectroscopic analysis.

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  3. null (Ed.)
    Emerging infrared photodetectors have reported a high level of gain using trap-assisted photomultiplication mechanisms enabling significant enhancements in their sensitivity. This work investigates a series of interfacial materials in order to understand how charge blocking layers facilitate trap-assisted photomultiplication in organic shortwave infrared detectors. The hole blocking layers induce accumulation of photogenerated holes at the interface, which in turn lowers the electron injection barrier and enables photomultiplication. In addition to examining photoresponse characteristics, the device dark current is analyzed by fitting to a charge injection model to quantify injection barriers. This demonstrates that the electric field induced barrier lowering effect plateaus with increasing applied bias. Among the interfaces studied, the best detectivity is observed using the hole blocking layer bathophenanthroline (Bphen), which reduces the probability of recombination and extends the lifetime of trapped holes to increase photomultiplication. This leads to a responsivity of 5.6 A W −1 (equivalent external quantum efficiency = 660% at 1050 nm) and detectivity of 10 9 Jones with broadband operation from 600 nm to 1400 nm. 
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