Helping semiconductors find a cooler way to relax

Bandgap engineering tin amended the show of optoelectronic devices that purpose to harness the vigor of "hot" electrons, probe from KAUST shows.

Semiconductors person a signature spot known arsenic the bandgap that fundamentally is simply a scope of forbidden electron energies. Electrons with an energy supra the apical of the bandgap are escaped to determination done the material, whereas those beneath the bottommost of the bandgap are not, and nary electrons with an vigor successful betwixt tin beryllium successful the material.

This elemental thought defines a semiconductor's optical properties. The vigor from immoderate absorbed light is transferred to the material's electrons. Most of the free electrons successful a semiconductor person an vigor adjacent the apical of the bandgap. But the absorption of photons with an vigor overmuch larger than the bandgap creates, successful turn, overmuch higher vigor electrons that are besides called "hot electrons."

Understanding the process by which these alleged blistery electrons unbend to an vigor nearer the apical of the bandgap is indispensable for knowing the cognition of light-harvesting devices. For example, the ratio of a star compartment is reduced if this immense excess vigor is mislaid arsenic heat. "However, it was highly difficult, if not impossible, to sufficiently utilize these hot electrons successful existent light-conversion applications owed to their precise abbreviated lifetimes," says worldly idiosyncratic Omar Mohammed.

Mohammed and his colleagues utilized interface and bandgap engineering to hold blistery carriers (electrons and holes) relaxation and to importantly summation their lifetimes.

The squad studied a semiconductor known arsenic a pb halide perovskite. They designed and fabricated architectures made up of aggregate quantum wells: a bladed furniture of semiconductor sandwiched betwixt light-absorber layers of larger bandgap material. They compared the optical properties of structures successful which the wells were each the aforesaid thickness and asymmetric structures successful which the good widths varied. They utilized a method called femtosecond (1 femtosecond = 10-15seconds) transient absorption spectroscopy combined with theoretical calculations to find the timescale of the blistery electron relaxation.

They recovered the cooling complaint had a beardown dependence connected the quantum good thickness successful the asymmetric illustration and that the relaxation of the blistery carriers successful the asymmetric aggregate quantum wells was 12.5-fold slower compared to that of the symmetric aggregate quantum wells.

"This caller uncovering provides a unsocial strategy connected however to importantly dilatory down the blistery carriers cooling successful semiconducting materials for their amended utilization successful star cells applications," says postdoc Partha Maity.

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More information: Partha Maity et al, Cascade Electron Transfer Induces Slow Hot Carrier Relaxation successful CsPbBr3 Asymmetric Quantum Wells, ACS Energy Letters (2021). DOI: 10.1021/acsenergylett.1c01142