Bioinspired, perovskite-based, wavelength-resolved UV-visible imaging sensors

Chen, Cheng

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https://hdl.handle.net/2142/121998 Copy

Description

Title

Bioinspired, perovskite-based, wavelength-resolved UV-visible imaging sensors

Author(s)

Chen, Cheng

Issue Date

2023-11-27

Director of Research (if dissertation) or Advisor (if thesis)

• Nie, Shuming
• Gruev, Viktor

Doctoral Committee Chair(s)

Nie, Shuming

Committee Member(s)

• Cunningham, Brian T
• Kim, Kyekyoon

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Perovskite nanocrystals
• UV imaging
• bioinspired
• resolving wavelengths

Abstract

Imaging and identifying target signatures and biomedical markers in the ultraviolet (UV) spectrum is broadly important to medical imaging, military target tracking, remote sensing, and industrial automation. However, current silicon-based imaging sensors face fundamental limitations due to the rapid absorption and attenuation of UV light, hindering their ability to resolve UV spectral signatures effectively. By applying fluorescent down-conversion materials, which transfer higher-energy photons to lower-energy photons, we may bypass the intrinsic limitations in efficiency of silicon-based photodetectors in the UV spectrums. Among all the fluorescent materials, perovskite nanocrystals (PNCs) stand out because of their flexible synthesis and excellent optoelectronic properties. In this thesis, I will document the synthesis of lead halide PNCs and their applications as downconversion materials in photodetection devices. Importantly, I will explain the development of a bioinspired, wavelength-resolved UV-visible imaging sensor by integrating inorganic PNCs with an array of vertically stacked silicon photodetectors. The sensor’s ability to differentiate between cancer cell lines and healthy cells based on spectral reconstruction will be demonstrated, as well as investigations into improving the stability of the device. In Chapter 2, I focused on synthesizing the all-inorganic PNCs and applying them on single photodiodes for enhanced quantum efficiency (QE) in the UV range. I proposed an architecture of silicon-based photodiodes which was coated by a PNC down-conversion layer on top. The photodiode's QE at 250nm was increased from < 1% to 30.5%, and the integrated QE from 250nm to 300nm was enhanced by 15.8 times after PNC coating. Furthermore, we enhanced the stability of the device by different methods, including surface modification and polymer encapsulation of the PNCs. Last but not least, the ion exchange between different types of PNCs was studied. This study provides a solution for high-efficiency photodetection in the UV spectrum and paved the way for applications of PNCs in imaging devices. In Chapter 3, a bioinspired CMOS camera for wavelength-resolved UV-visible imaging has been developed by using vertically stacked photodiode sensors and quantum-confined perovskite nanocrystals. The inspiration comes from the unique visual system of the Papilio xuthus butterfly, which has tetrachromatic vision and can detect UV light and resolve small spectral differences. A key design feature is the deposition of highly fluorescent perovskite nanocrystals on the microlenses of a high-resolution CMOS sensor chip, which absorbs and converts a portion of the UV signal to visible fluorescence. The remaining UV light passes through the microlens and is quickly attenuated and detected by the top photodiode. The combined signals arising from both visible fluorescence and direct UV absorption are detected by the photodiode’s RGB channels, which are digitally computed to yield hue-saturation-value (HSV) outputs. Remarkably, label-free fluorescence imaging data from various biomolecules and cancer/normal cells show that the use of standard computing algorithms for digital photography allows real-time imaging and wavelength differentiation of their intrinsic UV signatures at 99% confidence. In Chapter 4, a new architecture for developing low-cost, UV-wavelength-resolved photodiode arrays was established. Two nanocrystal-polymer films (NCPFs), with green and red PNCs respectively, were synthesized onto the vertically stacked photodiode arrays. Compared with our UV-wavelength-resolved camera proposed in chapter 3, this device has two key improvements: better stability due to encapsulation of the PNCs, and better discrimination over UV wavelengths due to the application of two different types of PNC layers at the same time. Applying the device, targets with illumination wavelengths from 300 nm to 400 nm were resolved. Furthermore, a retrieval algorithm for differentiating two UV wavelengths was established based on the outputs of the photodiode arrays.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Cheng Chen

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