03 Jul Perovskite pixel color filters: more light, higher resolution
Most image sensors are made of silicon. In order to build RGB sensors from them, the incident light must be filtered. Pixels for red contain filters that block green and blue. The same principle applies to green and blue pixels. Each pixel in a silicon image sensor therefore only receives around a third of the total amount of incident light.
Researchers at the Swiss Federal Institute of Technology in Zurich (ETH Zurich) and Empa, the ETH Domain’s interdisciplinary research institute for materials science and technology, have proposed a new solution that allows a camera to use all the light for color recording. According to the researchers their work is based on researching image sensors made of perovskite for almost ten years.
Stacked filters, chemically matched to the wavelength
The basis for the image sensor is the material lead halide perovskite. This crystalline material is a semiconductor. In contrast to silicon, however, it is particularly easy to process according to the researchers – and its physical properties vary with its exact chemical composition. This is precisely what the researchers are taking advantage of in the production of perovskite image sensors.
If the perovskite contains slightly more iodine ions, it absorbs red light. For green, the researchers add more bromine, for blue more chlorine – without any filters. The perovskite pixel layers remain transparent for the other wavelengths, allowing them to pass through. This means that the pixels for red, green and blue can be stacked on top of each other in the image sensor, unlike with silicon image sensors, where the pixels are next to each other.
Thanks to this arrangement, perovskite-based image sensors can theoretically capture three times as much light on the same surface area as conventional image sensors – and with three times the resolution. A few years ago, the team led by Maksym Kovalenko was able to demonstrate how they work, initially with individual oversized pixels made of millimeter-sized perovskite crystals. Now, for the first time, they are reporting on two functioning thin-film image sensors made of perovskite.
Perovskite image sensors can theoretically capture three times as much light on the same surface area as conventional silicon image sensors – with three times the resolution. Image: Sergii Yakunin / ETH Zurich / Empa)
From prototype to image sensor
“We are continuing to develop the technology from a rough proof of concept to a dimension where it could actually be used,” explains Kovalenko. The perovskite image sensors are still in the early stages of development. However, with two prototypes, the researchers can show that the technology can be miniaturized. Manufactured using industry-standard thin-film processes, the sensors have reached their target size, at least vertically, according to the researchers. “Of course, there is always potential for optimization,” says the scientist involved, Sergii Yakunin.
The researchers have thoroughly studied the two prototypes which differ in their readout technology in experiments. Their results prove the strengths of perovskite: the sensors are more sensitive to light, reproduce colors more precisely and can offer a significantly higher resolution than conventional silicon technology. The fact that each pixel captures the entire light also eliminates some of the artifacts of digital photography, such as demosaicing and the moiré effect.
Optimal filters for hyperspectral imaging
Digital cameras will not be the only area of application for perovskite image sensors. Due to the properties of perovskite, they are also particularly suitable for applications in the field of machine vision, the researchers emphasize. The focus on red, green and blue is based on the human eye: The image sensors work in RGB because our eyes see in RGB mode. For specific tasks, however, it is worth defining different wavelength ranges that are read out by a computer. There are often more than three – this is known as hyperspectral imaging.
Perovskite sensors have a decisive advantage for this type of imaging. Researchers can control the wavelength ranges that they absorb very precisely for each layer. “With perovskite, we can define numerous color channels that are clearly different from each other,” says Yakunin. Silicon, with its broad absorption spectrum, requires numerous filters and complex computer algorithms. “Even with a relatively small number of colors, this is very impractical,” says Kovalenko. Hyperspectral image sensors made from perovskite could be used in the field of medical analysis or automated monitoring of agriculture and the environment, for example.
Smaller pixels and more of them
In the next step, the researchers plan to make their perovskite image sensors even smaller and increase the number of pixels at the same time. Their two prototypes have pixel sizes between 0.5 mm and 1 mm. Pixels in commercial image sensors are in the micrometer range. “It should even be possible to make even smaller pixels from perovskite than from silicon,” says Yakunin. The electronic connections and processing techniques also need to be adapted for the new technology. “Today’s readout electronics are optimized for silicon. But perovskite is a different semiconductor, with different material properties,” says Kovalenko.
Original publication:
[S. Tsarev, D. Proniakova, X. Liu, E. Wu, G. Matt, K. Sakhatskyi, L. Ferraressi, R. Kothandaraman, F. Fu, I. Shorubalko, S. Yakunin, MV. Kovalenko; Vertically stacked monolithic perovskite colour photodetectors; Nature, DOI: 10.1038/s41586-025-09062-3.]
Source: ethz.ch
Image: ETH Zurich / Empa