Perovskite Sensors Promise True-Color Photos in Low Light

Researchers at Empa and ETH are working on a perovskite image sensor that has the potential to capture three times as much light and produce true-color images even in dimly lit environments. In contrast to traditional image sensors, which have red, green, and blue pixels arranged in a grid next to one another, perovskite pixels can be stacked, significantly boosting the amount of light that each pixel can capture.

Innovative light sensor: The researchers are now working on miniaturizing the pixels, which were originally up to five millimeters in size, and assembling them into a functioning image sensor.
Innovative light sensor: The researchers are now working on miniaturizing the pixels, which were originally up to five millimeters in size, and assembling them into a functioning image sensor. Image Credit: Empa

Today, capturing images of everything from family and friends to vacations and pets has become easy due to the ease of digital photography. Utilizing either smartphones or cameras, this widespread practice is supported by continual advancements in technology, with each new generation of devices boasting superior image sensors featuring an increased number of megapixels.

The most prevalent type of sensor employs silicon, which is segmented into pixels for red, green, and blue (RGB) light through specific filters. However, alternative methods for creating digital image sensors exist, some of which may offer improved performance.

A notable collaborative research initiative featuring contributions from Maksym Kovalenko of Empa's Thin Films and Photovoltaics laboratory, Ivan Shorubalko from Empa's Transport at Nanoscale Interfaces laboratory, and ETH Zurich researchers Taekwang Jang and Sergii Yakunin, is exploring an innovative alternative utilizing perovskite materials.

These researchers are developing an image sensor composed of perovskite, which demonstrates a markedly enhanced capacity for light capture compared to its silicon counterparts. Traditional silicon sensors arrange RGB pixels side by side, each capturing only about a third of the light it receives, with the remainder obstructed by the color filters.

In contrast, pixels composed of lead halide perovskites eliminate the need for separate color filters as the material inherently filters light.

Researchers at Empa and ETH Zurich have successfully engineered lead halide perovskites to absorb specific wavelengths—or colors—of light while remaining transparent to others. This design allows for the stacking of red, green, and blue pixels vertically rather than horizontally. Such a configuration enables these pixels to absorb the full spectrum of visible light.

A perovskite sensor could therefore capture three times as much light per area as a conventional silicon sensor.

Ivan Shorubalko, Researcher, Empa

Perovskite also increases the efficiency of the image sensor by converting a greater percentage of the absorbed light into an electrical signal.

In 2017, Kovalenko's group successfully created a single working stacked perovskite pixel for the first time. The electronics industry has partnered with Kovalenko's ETH-Empa consortium to take the next step toward real image sensors.

The challenges to address include finding new materials fabrication and patterning processes, as well as design and implementation of the perovskite-compatible read-out electronic architectures.

Maksym Kovalenko, Thin Films and Photovoltaics Lab, Empa

The researchers are now working on miniaturizing the pixels, which were originally up to 5 mm in size, and assembling them into a functioning image sensor.

In the laboratory, we don't produce the large sensors with several megapixels that are used in cameras. but with a sensor size of around 100'000 pixels, we can already show that the technology works.

Ivan Shorubalko, Researcher, Empa

Good Performance with Less Energy

Another significant benefit of perovskite-based image sensors lies in their manufacturing process. Unlike traditional semiconductors, perovskites are less susceptible to material defects, allowing for a relatively straightforward fabrication process. These can be deposited from a solution onto the substrate, simplifying the production method considerably.

In contrast, conventional image sensors require the use of high-purity monocrystalline silicon, which necessitates a complex production process involving temperatures nearing 1500 degrees Celsius.

Given these advantages, it is clear why perovskite-based image sensors are gaining traction. This interest is underscored by the involvement of industry partnerships in ongoing research projects. However, a notable challenge with perovskite technology is its stability; perovskite is more prone to degradation from environmental factors compared to the more robust silicon, presenting an area that requires further development.

Standard processes would destroy the material. So we are developing new processes in which the perovskite remains stable. And our partner groups at ETH Zurich are working on ensuring the stability of the image sensor during operation.

Ivan Shorubalko, Researcher, Empa

If the project concludes successfully by the end of 2025, the technology will be ready for industry adoption. Shorubalko is optimistic that the enhanced image sensor will attract cell phone manufacturers.

Many people today choose their smartphone based on the camera quality because they no longer have a stand-alone camera,” adds the researcher. A sensor capable of delivering excellent images even in significantly poorer lighting conditions could offer a substantial advantage.

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