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Optoelectronic Detectors Capable of Perceiving Light Intensity and Colour

Scientists develop a new low cost, flexible optoelectronic cell that can detect light intensity and perceive colour, inspired by human visual and psychological light perceptions.

Human brain can process a massive number of light signals at high speed, partly because it perceives lights as a combination of colours and intensities. However, the existing photodetectors can only indicate light intensities. It was recently reported that integrating dozens of photodetectors with semiconductors presenting different bandgaps can reconstruct spectral curves of incident lights. Nevertheless, such approach requires chip-level device assembly and signal-processing system, and can generate redundant signals for applications that do not need detailed spectral information.

In a paper published in Light Science & Application, a team of scientists, led by Professor Ding Shi-Jin from State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, China, have developed a low cost, flexible optoelectronic cell that can detect light intensity and perceive colour, inspired by human visual and psychological light perceptions.

Bandgap-gradient perovskites, prepared by a halide-exchanging method by dipping in a solution, are developed as the photoactive layer of the cell. Since photon absorption can only occur at energy levels above the bandgap of semiconductors, the devices can sense the spectral content of light signals with high resolution. The fabricated device produces two output signals; one showing linear responses to both photon energy and flux, while the other depends on only photon flux. Thus, by combining the two signals, the single device can project the monochromatic and broadband spectra into the total photon fluxes and average photon energy level, that are in similar to those obtained from a commercial photodetector and spectrometer. Adjusting illumination in real time, the prepared device can instantaneously provide intensity and hue results.

The colorimetric chemical- and bio-assay was also demonstrated in the study. Chemical- and bio-analytes will modify the colour of the sensing material, and the bandgap-gradient device will convert the colour change to an electrical signal. For this simple proof of concept, a pH testing paper was used. When using a single silicon photodiode output current, colour differences due to pH were not detectable. Spectral curves of the pH testing paper under the same illumination measured by a spectrometer could distinguish the different colours by presenting different peak positions. However, this method not only requires bulky equipment but also generates spectral information that is redundant for sensing applications. The response of the bandgap-gradient device can clearly distinguish between the various pH values. Therefore, the colour-perception device effectively achieves colorimetric chemical- and bio-sensing with only a single device and by generating only one or two current signals.

The team of scientists shared that bandgap-gradient structures with high degrees of control can be achieved by other fabrication technologies with processing parameters that can produce a gradient. Colour-perception devices with excellent performance, small size and the structure capable of integration would be achieved by further optimizing the selection of the optoelectronic material and the design of the bandgap-gradient structure.

They were also optimistic that the device can be used in colour-sensing pixels, which may be more simplified than existing devices containing several photodetectors and optical filters. Multifunctional sensors can be produced by combining devices with stimuli-responsive materials to detect physical, chemical, or biological stimuli through a comparison of colours.

This work could potentially lead to the creation of a new category of optoelectronic devices that are capable of spectrum projection and hue perception, thereby opening up a range of applications. [APBN]