School of Chemistry - Research Publications

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Author: Bullock, James × Author: Mulvaney, Paul × End date: 2024 × Start date: 2020 ×

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    Room Temperature Bias-Selectable, Dual-Band Infrared Detectors Based on Lead Sulfide Colloidal Quantum Dots and Black Phosphorus
    Wang, S ; Ashokan, A ; Balendhran, S ; Yan, W ; Johnson, BC ; Peruzzo, A ; Crozier, KB ; Mulvaney, P ; Bullock, J (AMER CHEMICAL SOC, 2023-06-15)
    A single photodetector capable of switching its peak spectral photoresponse between two wavelength bands is highly useful, particularly for the infrared (IR) bands in applications such as remote sensing, object identification, and chemical sensing. Technologies exist for achieving dual-band IR detection with bulk III-V and II-VI materials, but the high cost and complexity as well as the necessity for active cooling associated with some of these technologies preclude their widespread adoption. In this study, we leverage the advantages of low-dimensional materials to demonstrate a bias-selectable dual-band IR detector that operates at room temperature by using lead sulfide colloidal quantum dots and black phosphorus nanosheets. By switching between zero and forward bias, these detectors switch peak photosensitive ranges between the mid- and short-wave IR bands with room temperature detectivities of 5 × 109 and 1.6 × 1011 cm Hz1/2 W-1, respectively. To the best of our knowledge, these are the highest reported room temperature values for low-dimensional material dual-band IR detectors to date. Unlike conventional bias-selectable detectors, which utilize a set of back-to-back photodiodes, we demonstrate that under zero/forward bias conditions the device's operation mode instead changes between a photodiode and a phototransistor, allowing additional functionalities that the conventional structure cannot provide.
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    Flexible Vanadium Dioxide Photodetectors for Visible to Longwave Infrared Detection at Room Temperature ((press release associated article should be online on 21.06.2023))
    Balendhran, S ; Taha, M ; Wang, S ; Yan, W ; Higashitarumizu, N ; Wen, D ; Azar, NS ; Bullock, J ; Mulvaney, P ; Javey, A ; Crozier, KB (WILEY-V C H VERLAG GMBH, 2023-10-13)
    Abstract Flexible optoelectronics is a rapidly growing field, with a wide range of potential applications. From wearable sensors to bendable solar cells, curved displays, and curved focal plane arrays, the possibilities are endless. The criticality of flexible photodetectors for many of these applications is acknowledged, however, devices that are demonstrated thus far are limited in their spectral range. In this study, flexible photodetectors are demonstrated using a VOx nanoparticle ink, with an extremely broad operating wavelength range of 0.4 to 20 µm. This ink is synthesized using a simple and scalable wet‐chemical process. These photodetectors operate at room temperature and exhibit minimal variance in performance even when bent at angles of up to 100 ° at a bend radius of 6.4 mm. In addition, rigorous strain testing of 100 bend and release cycles revealed a photoresponse with a standard deviation of only 0.55%. This combination of mechanical flexibility, wide spectral response, and ease of fabrication makes these devices highly desirable for a wide range of applications, including low‐cost wearable sensors and hyperspectral imaging systems.
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    An ITO-Free Kesterite Solar Cell
    Ji, Y ; Chen, W ; Yan, D ; Bullock, J ; Xu, Y ; Su, Z ; Yang, W ; Laird, JS ; Zheng, T ; Wu, N ; Zha, W ; Luo, Q ; Ma, C-Q ; Smith, TA ; Liu, F ; Mulvaney, P (WILEY-V C H VERLAG GMBH, 2024-02)
    Photovoltaic thin film solar cells based on kesterite Cu2 ZnSn(S, Se)4 (CZTSSe) have reached 13.8% sunlight-to-electricity conversion efficiency. However, this efficiency is still far from the Shockley-Queisser radiative limit and is hindered by the significant deficit in open circuit voltage (VOC ). The presence of high-density interface states between the absorber layer and buffer or window layer leads to the recombination of photogenerated carriers, thereby reducing effective carrier collection. To tackle this issue, a new window structure ZnO/AgNW/ZnO/AgNW (ZAZA) comprising layers of ZnO and silver nanowires (AgNWs) is proposed. This structure offers a simple and low-damage processing method, resulting in improved optoelectronic properties and junction quality. The ZAZA-based devices exhibit enhanced VOC due to the higher built-in voltage (Vbi ) and reduced interface recombination compared to the usual indium tin oxide (ITO) based structures. Additionally, improved carrier collection is demonstrated as a result of the shortened collection paths and the more uniform carrier lifetime distribution. These advances enable the fabrication of the first ITO-free CZTSSe solar cells with over 10% efficiency without an anti-reflective coating.