Exceeding 100 percent quantitative efficiency in the photocurrent of mixed inorganic-organic semiconductors

Exceeding 100 percent quantitative efficiency in the photocurrent of mixed inorganic-organic semiconductors

By fabricating a semiconductor material containing tin-based nanoparticles known as quantum dots, an international team of researchers including KAUST has achieved an astonishing conversion of optical energy. Credit: KAUST/Hino Huang

Small crystals, known as quantum dots, enabled an international team to achieve a quantum efficiency of over 100 percent in the photocurrent generated in mixed inorganic semiconductors.

Perovskites are an exciting semiconductor for light-harvesting applications and have already shown some impressive performance in solar cells. But improvements in image conversion efficiency are necessary to transfer this technology to a broader market.

Light comes in bundles of energy known as photons. When a photon is absorbed by a semiconductor, electromagnetic energy is transmitted to a negatively charged electron and to its positively charged counterpart, known as a hole. An electric field can sweep these particles in opposite directions, allowing current to flow. This is the basic process of a solar cell. It may sound simple, but improving quantum efficiency, or getting as many electron-hole pairs as possible from incoming photons, has been a long-standing goal.

One reason for the inefficiency is that if a photon contains 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 dots, can transform high-energy photons into more than one pair of electron-holes.

Jun Yin and Omar Muhammad of KAUST worked with Yifan Chen and Mingjie Li of Hong Kong Polytechnic University and their colleagues to demonstrate so-called multiple exciton generation (MEG) in lead-tin halide perovskite nanocrystals. “We have demonstrated photocurrent quantum efficiencies exceeding 100 percent by harnessing MEG in perovskite nanodevices,” says Yin.

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

Materials with narrower bandgaps present a greater challenge because the excited electron-hole pairs either relax or cool too quickly to be extracted into a working solar cell device. “The efficiency of MEG in narrow bandgap perovskite nanocrystals and verification of MEG inherent in practical optical devices has not been reported,” says Yin.

Chen, Yin and the team made a semiconductor material composed of fine particles of tin formidium – perovskite iodide – made using small amounts of tin – embedded in tin-free FAPbI.3. The team believes that introducing tin helps slow down the “cooling”. “We will be able to further improve the perovskite nanocrystals by changing their composition to get higher MEG performance and improve light energy conversion,” says Yin.

The search was published in Nature Photonics.

Helping semiconductors find a cooler way to relax

more information:
Yifan Chen et al, Multiple exciton generation in tin-lead perovskite nanocrystals to enhance photocurrent quantum efficiency, Nature Photonics (2022). DOI: 10.1038 / s41566-022-01006-x

Presented by King Abdullah University of Science and Technology

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