Towards Infrared Electronic Eyes: Flexible Colloidal Quantum Dot Photovoltaic Detectors Enhanced by Resonant Cavity

Abstract

Electronic eye cameras are receiving increasing interest due to their unique advantages such as wide field of view, low aberrations, and simple imaging optics compared to conventional planar focal plane arrays. However, the spectral sensing ranges of most electronic eyes are confined to the visible, which is limited by the energy gaps of the sensing materials and by fabrication obstacles. Here, a potential route leading to infrared electronic eyes is demonstrated by exploring flexible colloidal quantum dot (CQD) photovoltaic detectors. Benefitting from their tunable optical response and the ease of fabrication as solution processable materials, mercury telluride (HgTe) CQD detectors with mechanical flexibility, wide spectral sensing range, fast response, and high detectivity are demonstrated. A strategy is provided to further enhance the light absorption in flexible detectors by integrating a Fabry–Perot resonant cavity. Integrated short‐wave IR detectors on flexible substrates have peak D* of 7.5 × 1010 Jones at 2.2 µm at room temperature and promise the development of infrared electronic eyes with high‐resolution imaging capability. Finally, infrared images are captured with the flexible CQD detectors at varying bending conditions, showing a practical approach to sensitive infrared electronic eyes beyond the visible range.

HgTe Nanocrystal Inks for Extended Short‐Wave Infrared Detection

“…The IV curve reveals a rectifying behavior even at room temperature (see Figure d), with a weak dark current (<10 −6 A cm −2 ) around 0 V. Under black body illumination (65 µW, corresponding to integrated power from 1.9 µm to the HgTe 4k cut‐off), the responsivity of the device has been determined to be 20 mA W −1 , see Figure e and Figure S9 (Supporting Information). This is almost two orders of magnitude higher than previously reported devices at the same wavelength based on HgTe nanocrystals, and only diodes with optical resonators have achieved higher responsivities. This is the result of (i) a higher absorption thanks to a thicker HgTe film.…”

“…Under colloidal form, HgTe is certainly the most mature material combining infrared absorption and photoconduction . On the other hand, efforts dedicated to the integration of HgTe nanocrystals into photodiodes are much fewer than those reported for PbS. As a result, most devices based on HgTe nanocrystals with long wavelength absorption are based on planar geometries …”

Tunable self‐powered n‐SrTiO3 photodetectors based on varying CuS‐ZnS nanocomposite film (p‐CuZnS, p‐CuS, and n‐ZnS)

“…Photodetectors, which detect irradiation directly by transforming light into electrical signals based on photoelectric effect, have been extensively used in various applications, such as environmental monitoring, biological/chemical analysis, flame detection, and communications . Recently, many groups are dedicated to realizing photodetectors with self‐powered characteristics .…”

“…Photodetectors, which detect irradiation directly by transforming light into electrical signals based on photoelectric effect, have been extensively used in various applications, such as environmental monitoring, biological/chemical analysis, flame detection, and communications. [1][2][3][4][5][6][7] Recently, many groups are dedicated to realizing photodetectors with self-powered characteristics. [8][9][10][11][12] The self-powered devices can work under zero bias due to the photovoltaic effect from p-n junctions or heterojunctions under light illumination, and are particularly appealing for their miniaturization and portability.…”

Designing Photovoltaic Devices Using HgTe Nanocrystals for Short and Mid‐Wave Infrared Detection

“…Integration of the material is no longer limited to a single pixel in planar geometry. Also, proof of concept for flexible substrate and deposition on focal plane array have been obtained . Maturity of the material has become good enough to start considering stability issues: low temperature operation or encapsulation allow operation of the devices over several months .…”