More than 100 percent quantum efficiency in the photocurrent of a hybrid inorganic-organic semiconductor

Getting more out of light

By synthesizing a semiconducting material with tin-based nanoparticles known as quantum dots, an international team of researchers, including KAUST, achieved an impressive conversion from light to power. Credit: KAUST/Heno Hwang

Tiny crystals, known as quantum dots, have enabled an international team to achieve a quantum efficiency of more than 100 percent in the photocurrent generated in a hybrid inorganic-organic semiconductor.

Perovskites are exciting semiconductors for light harvesting applications and have already shown some impressive performance in solar cells. But improvements in photo conversion efficiency are needed to bring this technology to a wider market.

Light comes in packets of energy called photons. When a semiconductor absorbs a photon, electromagnetic energy is transferred to a negatively charged electron and its positively charged counterpart, known as a hole. A electric field can sweep these particles in opposite directionsthrough which a current can flow. This is the basic operation of a solar cell. It may sound simple, but optimizing quantum efficiency, or getting that many electron-hole pairs of the incoming photons has long been a goal.

One cause of inefficiency is that if the photon has more energy than is needed to create the electron-hole pair, the excess energy is usually lost as heat. But nanomaterials offer a solution. Small particles, such as nanocrystals or quantum dotscan convert high-energy photons into more than one electron-hole pair.

Jun Yin and Omar Mohammed from KAUST collaborated with Yifan Chen and Mingjie Li from Hong Kong Polytechnic University and their colleagues to demonstrate this so-called multiple exciton generation (MEG) in tin-lead halide-perovskite nanocrystals. “We have demonstrated a photostream quantum efficiency more than 100 percent by using MEG in the perovskite nanocrystals,” says Yin.

In the past, MEG has been observed in large bandgap perovskite nanocrystals: that is, those semiconductors that can only absorb high-energy photons.

Materials with a narrower bandgap are more challenging because the excited electron-hole pairs relax or cool too quickly to be extracted in a functioning solar cell device. “Efficient MEG in narrower bandgap perovskite nanocrystals and verification of their inherent MEG in practical optical devices have not been reported,” Yin says.

Chen, Yin and team synthesized a semiconducting material made up of tiny particles of formamidinium tin-lead iodide perovskite – made with small amounts of tin – embedded in tin-free FAPbI3. The team believes the introduction of tin helps to slow down the “cooling”. “We will be able to further optimize the perovskite nanocrystal by changing its composition to obtain higher MEG performance and improve light-energy conversion,” Yin says.

The research was published in Nature photonics.


Semiconductors help find a cooler way to relax


More information:
Yifan Chen et al, Multiple exciton generation in tin-lead halide perovskite nanocrystals for improving photocurrent quantum efficiency, Nature photonics (2022). DOI: 10.1038/s41566-022-01006-x

Quote: More than 100 percent quantum efficiency in the photocurrent of a hybrid inorganic-organic semiconductor (2022, August 4), retrieved August 4, 2022 from https://phys.org/news/2022-08-exceeding-percent-quantum-efficiency -photocurrent .html

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