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1. Elucidating the Detectivity Limits in Shortwave Infrared Organic Photodiodes

   https://doi.org/10.1002/adfm.201800391  

   Wu, Zhenghui ; Yao, Weichuan ; London, Alexander E. ; Azoulay, Jason D. ; Ng, Tse Nga ( March 2018 , Advanced Functional Materials)

   While only few organic photodiodes have photoresponse past 1 µm, novel shortwave infrared (SWIR) polymers are emerging, and a better understanding of the limiting factors in narrow bandgap devices is critically needed to predict and advance performance. Based on state‐of‐the‐art SWIR bulk heterojunction photodiodes, this work demonstrates a model that accounts for the increasing electric‐field dependence of photocurrent in narrow bandgap materials. This physical model offers an expedient method to pinpoint the origins of efficiency losses, by decoupling the exciton dissociation efficiency and charge collection efficiency in photocurrent–voltage measurements. These results from transient photoconductivity measurements indicate that the main loss is due to poor exciton dissociation, particularly significant in photodiodes with low‐energy charge‐transfer states. Direct measurements of the noise components are analyzed to caution against using assumptions that could lead to an overestimation of detectivity. The devices show a peak detectivity of 5 × 10¹⁰Jones with a spectral range up to 1.55 µm. The photodiodes are demonstrated to quantify the ethanol–water content in a mixture within 1% accuracy, conveying the potential of organics to enable economical, scalable detectors for SWIR spectroscopy.

    

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2. Phase-modulated axilenses for infrared multiband spectroscopy

   https://doi.org/10.1364/OL.388704  

   Chen, Yuyao ; Britton, Wesley A. ; Dal Negro, Luca ( April 2020 , Optics Letters)

   We design and characterize compact phase-modulated axilens devices that combine efficient point focusing and grating selectivity within four-level phase mask configurations. Specifically, we select and characterize in detail two device configurations designed for long-wavelength infrared (LWIR) operation in the$6\text{µ<\#comment/>}\mathrm{m}-<\#comment/>12\text{µ<\#comment/>}\mathrm{m}$wavelength range. These devices are ideally suited for monolithic integration atop the substrate layers of infrared focal plane arrays (IR-FPAs) for use in multiband LWIR photodetection. We systematically study their focusing efficiency, spectral response, and crosstalk ratio, and we demonstrate a single-component microspectrometer. Our design method leverages the Rayleigh–Sommerfeld (RS) diffraction theory that is validated numerically using the finite element method (FEM). The proposed devices are broadband and polarization insensitive and add fundamental spectroscopic capabilities to miniaturized optical components for a number of applications in LWIR detection and spectroscopy.

    

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3. A General Strategy for Enhancing Sensitivity and Suppressing Noise in Infrared Organic Photodetectors Using Non‐Conjugated Polymer Additives

   https://doi.org/10.1002/adfm.202314210  

   Bills, Tyler ; Liu, Chih‐Ting ; Lim, Jasmine ; Eedugurala, Naresh ; Mahalingavelar, Paramasivam ; Seo, Bogyeom ; Hanna, Ethan T. ; Ng, Tse Nga ; Azoulay, Jason D. ( February 2024 , Advanced Functional Materials)

   Photodetectors operating across the near‐ to short‐wave infrared (NIR–SWIR,λ= 0.9–1.8 µm) underpin modern science, technology, and society. Organic photodiodes (OPDs) based on bulk‐heterojunction (BHJ) active layers overcome critical manufacturing and operating drawbacks inherent to crystalline inorganic semiconductors, offering the potential for low‐cost, uncooled, mechanically compliant, and ubiquitous infrared technologies. A constraining feature of these narrow bandgap materials systems is the high noise current under an applied bias, resulting in specific detectivities (D^*, the figure of merit for detector sensitivity) that are too low for practical utilization. Here, this study demonstrates that incorporating wide‐bandgap insulating polymers within the BHJ suppresses noise by diluting the transport and trapping sites as determined using capacitance‐frequency analysis. The resultingD^*of NIR–SWIR OPDs operating from 600–1400 nm under an applied bias of −2 V is improved by two orders of magnitude, from 10⁸to 10¹⁰ Jones (cm Hz^1/2 W⁻¹), when incorporating polysulfone within the blends. This broadly applicable strategy can reduce noise in IR‐OPDs enabling their practical operation and the realization of emerging technologies.

    

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4. A Highly Sensitive UV–vis–NIR All‐Inorganic Perovskite Quantum Dot Phototransistor Based on a Layered Heterojunction

   https://doi.org/10.1002/adom.201800324  

   Zou, Chen ; Xi, Yuyin ; Huang, Chun‐Ying ; Keeler, Ethan G. ; Feng, Tianyu ; Zhu, Shihao ; Pozzo, Lilo D. ; Lin, Lih Y. ( May 2018 , Advanced Optical Materials)

   All‐inorganic perovskite quantum dots (IPQDs) are a promising material for use in various optoelectronic devices due to their excellent optoelectronic properties and high environmental stability. Here, a high‐performance phototransistor based on a layered heterojunction composed of CsPbI₃QDs and a narrow‐bandgap conjugated polymer DPP‐DTT is reported, which shows a high responsivity of 110 A W⁻¹, a specific detectivity of 2.9 × 10¹³Jones and a light to dark current ratio up to 6 × 10³. The heterojunction phototransistor exhibits unipolar p‐type and gate bias modulated behaviors. In addition, the device exhibits a broad spectral detection range from ultraviolet to near infrared. The high sensitivity of the device is attributed to the layered heterojunction and the gate bias modulation property. The work overcomes the existing limitations in sensitivity of IPQD photodetectors due to the poor charge transport between QDs. The convenient solution‐processed fabrication and excellent device performance especially suggest the IPQD/narrow‐bandgap conjugate polymer heterojunction as a promising structure for potential applications of ultrasensitive broadband photodetectors compatible with a wide variety of substrates.

    

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5. Interlayer Transition in a vdW Heterostructure toward Ultrahigh Detectivity Shortwave Infrared Photodetectors

   https://doi.org/10.1002/adfm.201905687  

   Qi, Tailei ; Gong, Youpin ; Li, Alei ; Ma, Xiaoming ; Wang, Peipei ; Huang, Rui ; Liu, Chang ; Sakidja, Ridwan ; Wu, Judy Z. ; Chen, Rui ; et al ( October 2019 , Advanced Functional Materials)

   Van der Waals (vdW) heterostructures of 2D atomically thin layered materials (2DLMs) provide a unique platform for constructing optoelectronic devices by staking 2D atomic sheets with unprecedented functionality and performance. A particular advantage of these vdW heterostructures is the energy band engineering of 2DLMs to achieve interlayer excitons through type‐II band alignment, enabling spectral range exceeding the cutoff wavelengths of the individual atomic sheets in the 2DLM. Herein, the high performance of GaTe/InSe vdW heterostructures device is reported. Unexpectedly, this GaTe/InSe vdWs p–n junction exhibits extraordinary detectivity in a new shortwave infrared (SWIR) spectrum, which is forbidden by the respective bandgap limits for the constituent GaTe (bandgap of ≈1.70 eV in both the bulk and monolayer) and InSe (bandgap of ≈1.20–1.80 eV depending on thickness reduction from bulk to monolayer). Specifically, the uncooled SWIR detectivity is up to ≈10¹⁴Jones at 1064 nm and ≈10¹²Jones at 1550 nm, respectively. This result indicates that the 2DLM vdW heterostructures with type‐II band alignment produce an interlayer exciton transition, and this advantage can offer a viable strategy for devising high‐performance optoelectronics in SWIR or even longer wavelengths beyond the individual limitations of the bandgaps and heteroepitaxy of the constituent atomic layers.

    

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