First Authors: Yiming Zhao and Artem V. Kuklin
Corresponding Authors: Ying Li, Hans Ågren, and Lingfeng Gao
DOI: 10.1002/lpor.202503087
Photoelectrochemical (PEC) photodetectors (PDs) have attracted increasing attention because of their simple fabrication processes and low cost, giving them broad application prospects in environmental monitoring, imaging, optical communications, and other fields. Quantum dots (QDs), featuring size-tunable optical properties, high absorption coefficients, and solution processability, are considered promising materials for next-generation photodetectors. However, single-component quantum dots often suffer from poor stability, rapid carrier recombination, and limited spectral response ranges, restricting their practical applications. Constructing core-shell heterojunctions is an effective strategy for optimizing the performance of quantum dots. This approach can regulate electronic structures, suppress surface recombination, preserve quantum-confinement effects, and improve the optical properties and stability of devices through the shell material.
Recently, Professor Ying Li from Zhejiang University of Technology, Professor Hans Ågren from Uppsala University, and Associate Professor Lingfeng Gao from Hangzhou Normal University jointly reported a strategy for preparing uniform Te@Se core-shell quantum dots by combining liquid-phase exfoliation with epitaxial growth, as illustrated in Figure 1. By taking advantage of the highly compatible lattice structures of Te and Se, which belong to the same group of elements, the researchers successfully overcame the lattice-mismatch challenge commonly encountered in the synthesis of core-shell materials.
The research team systematically investigated the photoresponse performance of Te@Se QD-based PEC photodetectors in low-concentration electrolytes ranging from 0.1 to 10 mM, as well as in pure water. The device exhibited excellent broadband photoresponse characteristics across the wavelength range of 365–700 nm. By optimizing the applied bias voltage and incident-light power density, a photocurrent density (Pph) of up to 32.63 µA/cm2 and a photoresponsivity (Rph) of 1564 µA/W were achieved.
In addition, the detector demonstrated a rapid response and excellent long-term stability in deionized water, with a performance degradation of only approximately 2.4% over 10,000 seconds. This study not only provides a new strategy for preparing high-quality core-shell quantum dots, but also demonstrates high-performance photodetection in low-concentration and mild electrolyte environments. It effectively addresses the dependence of conventional PEC devices on highly concentrated and corrosive electrolytes, substantially expanding their potential applications in wearable, biocompatible, and environmentally friendly optoelectronic devices.
Figure 1. Schematic illustration of the synthesis of Te@Se core-shell quantum dots.
Figure 2. (a) TEM and HRTEM images of Te quantum dots and their corresponding particle-size distribution. (b) AFM image of Te quantum dots and the corresponding thickness distribution. (c) TEM and HRTEM images of Te@Se quantum dots and their corresponding particle-size distribution. (d) AFM image of Te@Se quantum dots and the corresponding thickness distribution.
The morphology and particle sizes of the Te@Se core-shell quantum dots were characterized using transmission electron microscopy (TEM) and atomic force microscopy (AFM). As shown in Figure 2, the Te QDs exhibited a nearly spherical structure, with an average particle size of approximately 2.5 nm and an average thickness of approximately 2.0 nm.
The core-shell structure of the Te@Se QDs can be clearly observed in the HRTEM images. Their average particle size was approximately 3.3 nm, while the inner and outer lattice spacings corresponded to the characteristic crystal planes of Te and Se, respectively. AFM measurements revealed an average thickness of approximately 3.1 nm, confirming the successful epitaxial growth of the Se shell on the surface of the Te core.
Figure 3. (a) Optimized geometrical structures of the (100) and (110) heterojunctions. Te and Se atoms are represented by dark-green and light-green spheres, respectively. (b) Electron localization function (ELF) maps of the Se/Te (100) heterojunction, upper panel, and the Se/Te (110) heterojunction, lower panel. Red represents fully localized electrons, while green represents fully delocalized electrons. (c) Plane-averaged electrostatic potentials of the Se/Te (100) and (110) heterojunctions calculated along the z direction. (d) Projected band structures of Se atoms, indicated by green circles, and Te atoms, indicated by blue circles. The Fermi level is set to 0 eV. (e) Schematic illustrations of the band alignments in the Se/Te (100) and (110) heterojunctions. (f) Normalized absorption spectra of Se (110) and Te (110).
Density functional theory (DFT) calculations were performed on the electronic structures of the Se/Te (100) and (110) heterojunctions to clarify the photoresponse mechanism of the Te@Se core-shell quantum dots. As shown in Figure 3a, supercell models composed of five layers of Se and Te were constructed.
The ELF maps in Figure 3b show that electrons at the heterojunction interfaces are delocalized, indicating a relatively weak interaction between Te and Se. Bader charge analysis further confirmed that approximately 0.3–0.5 e− was transferred from the Te core to the Se shell. This charge transfer is consistent with the difference between the work functions of Te and Se, as shown in Figure 3c. Because Te has a lower work function and therefore a higher Fermi level, electrons migrate from Te to Se after contact, resulting in the formation of an interfacial dipole.
The calculated band structures in Figure 3d indicate that both heterojunctions are direct narrow-bandgap semiconductors, with bandgaps of 0.40 eV and 0.35 eV, respectively. They exhibit type-I heterojunction characteristics, as illustrated in Figure 3e. Both the valence band and conduction band of Te lie within the bandgap of Se, allowing photogenerated electrons and holes to be confined within the Te layer.
Furthermore, the DFT-calculated absorption spectra shown in Figure 3f indicate that Se mainly responds to ultraviolet light, whereas Te covers the visible-light region. The resulting heterojunction therefore achieves broadband absorption from ultraviolet to visible wavelengths, theoretically explaining the intrinsic origin of the broadband photoresponse of the Te@Se QDs.
Figure 4. Performance of Te@Se QD-based photodetectors under simulated-light illumination: (a) LSV curves in different electrolytes. (b) Photoresponse behavior in different 10−4 M electrolytes and deionized water. (c) EIS spectra in different 10−4 M electrolytes and deionized water. (d) Photoresponse behavior in electrolytes of different concentrations at a light-power density (Pλ) of 43 mW/cm2. (e) Photoresponse behavior under different applied bias voltages in 0.01 M Na2SO4. (f) Fitting results for Pph and Pλ. (g) Fitting results for Rph and Pλ. (h) Calculated Pph as a function of bias voltage. (i) Calculated Rph as a function of bias voltage.
As shown in Figure 4, the effects of electrolyte type, applied bias voltage, and incident-light power density on the photoelectrochemical response of the Te@Se QD-based detector were systematically investigated.
The LSV curves shown in Figure 4a confirm that the Te@Se QD material exhibits no obvious oxidation or reduction peaks in low-concentration acidic, alkaline, and neutral electrolytes or in deionized water, demonstrating its excellent electrochemical stability. Figure 4b shows that clear photocurrents and stable light on/off signals can be obtained in various 10−4 M electrolytes and in deionized water. The EIS spectra in Figure 4c reveal that the slightly lower photocurrent in deionized water results from its relatively high impedance.
Figures 4d–4i illustrate the effects of electrolyte concentration, applied bias voltage, and incident-light power density on the device’s photoelectrochemical performance. Increasing the applied bias voltage effectively suppresses the recombination of photogenerated charge carriers. The optimal photoelectrochemical performance was achieved at a bias voltage of −0.6 V. In addition, the relationships of photocurrent density and photoresponsivity with incident-light power density and applied bias voltage can be accurately fitted using power-law functions and exponential asymptotic functions, respectively.
Figure 5. Performance of the Te@Se QD-based photodetector in deionized water: (a) Photoresponse behavior under simulated-light illumination at different applied bias voltages. (b) Representative light on/off signals at the fourth light-intensity level. (c) Photoresponse behavior under illumination at different wavelengths. (d) Response and recovery times under illumination at different wavelengths, in seconds. (e) Long-term stability tests involving 1,000 cycles for a freshly prepared sample and a sample stored for one month. (f) Representative light on/off signals extracted from the time intervals of 4,800–4,900 seconds and 9,800–9,900 seconds.
As shown in Figures 5a–5c, the Te@Se QD-based detector exhibits outstanding photoelectrochemical performance in pure water. Stable light on/off signals were observed at each applied bias voltage, and the photocurrent increased substantially with increasing bias voltage and incident-light power density. Clear photoresponse signals were detected across the entire wavelength range of 365–700 nm, demonstrating excellent broadband photodetection capability.
To evaluate its potential for practical applications, the response speed and long-term stability of the Te@Se QD-based detector were also investigated. As shown in Figures 5d–5f, the detector exhibited rapid response and recovery characteristics under illumination at different wavelengths. Charge carriers were generated rapidly under illumination, whereas their recombination proceeded more slowly under dark conditions.
During the 10,000-second long-term cycling test, the freshly prepared sample retained 97.6% of its initial photocurrent, while the sample stored for one month retained 95.2%. Only slight performance degradation was observed, fully demonstrating the outstanding long-term stability of the device.
The related work was recently published in Laser & Photonics Reviews. The first authors are Yiming Zhao, a doctoral student at Zhejiang University of Technology, and Artem V. Kuklin, a postdoctoral researcher at Uppsala University. Professor Ying Li of Zhejiang University of Technology, Professor Hans Ågren of Uppsala University, and Associate Professor Lingfeng Gao of Hangzhou Normal University are the co-corresponding authors.
Ying Li: Professor at the College of Chemical Engineering, Zhejiang University of Technology. Professor Li has led multiple national-level research projects and major industry-sponsored projects and has published more than 400 SCI-indexed papers. Professor Li has filed over 80 patent applications, several of which have been successfully commercialized.
The ultra-stable, low-mercury catalysts developed by the research team have been widely used in the polyvinyl chloride industry. Two carbon-supported catalyst production lines, each with an annual capacity exceeding 3,000 metric tons, have been established in Guizhou and Inner Mongolia.
Professor Li’s research focuses on the controlled synthesis of carbon-based materials and their applications in adsorption and catalysis. Major research topics include catalysts for producing vinyl chloride monomers from coal-based acetylene, the design and synthesis of carbon-supported metal catalysts for liquid-phase hydrogenation, and the development of low-temperature ruthenium-on-carbon catalysts for ammonia synthesis.
In March 2024, Professor Li founded Huzhou Jiatan New Materials Technology Co., Ltd. The company has received support from the South Taihu Lake Entrepreneurship Program for High-Level Talent in Huzhou, Zhejiang Province, and is dedicated to the research, development, industrialization, and application of carbon-based materials for industrial catalysis and green chemical processes.
Hans Ågren: Founder of the Department of Theoretical Chemistry and Biology at the KTH Royal Institute of Technology in Sweden. Professor Ågren completed his doctoral research under Nobel laureate Kai Siegbahn. In 1981, he became an assistant professor of quantum chemistry at Lund University. In 1991, he served as the founding chair of the Computational Physics Research Center at Linköping University. In 1998, he became the founding chair of the School of Theoretical Chemistry at KTH Royal Institute of Technology.
Professor Ågren is a recipient of the Swedish Bjurzon Prize and the Björn Roos Prize and has served as a Changjiang Scholar Chair Professor of the Chinese Ministry of Education at Harbin Institute of Technology. His research focuses on theoretical chemistry and related interdisciplinary fields, including molecular, nanoscale, and biological photonics and electronics, photocatalysis, and X-ray spectroscopy and diffraction.
Lingfeng Gao: Associate Professor at the College of Materials, Chemistry and Chemical Engineering, Hangzhou Normal University. His research focuses primarily on the preparation of emerging low-dimensional nanomaterials and their photoelectric sensing properties.
As a first or corresponding author, Associate Professor Gao has published more than 40 SCI-indexed papers in major international journals, including four highly cited papers and one hot paper. His publications have received more than 3,900 citations, and his H-index is 31.
In 2019, he was selected for the Shenzhen Peacock Program as a Category C Overseas High-Level Talent. In 2021, he was recognized as a Category D High-Level Talent in Hangzhou. He has led research projects funded by the National Natural Science Foundation of China and the Natural Science Foundation of Zhejiang Province.
Yiming Zhao, Artem V. Kuklin, Jiahui Hou, et al. “Synthesis of Core-Shell Te@Se Quantum Dots and Their Broadband Photodetector Performance in Low Concentration Electrolytes.” Laser & Photonics Reviews, 2026, e03087. DOI: 10.1002/lpor.202503087.
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