Quantum dots keep their glow under heat after dual modification

Quantum dots, tiny semiconductor crystals just a few nanometers across, shine brightly with precise color control for use in LEDs, displays and solar cells. However, high temperatures pose a significant challenge to their practical applications. A research team at Koç University has found that modifying both the internal crystal structure and surface of perovskite quantum dots can greatly enhance their thermal stability.

In untreated quantum dots, structural integrity and light emission begin to decline at around 60°C (140°F), while modified materials maintained their properties up to 80°C (176°F). The study, published in the open-access journal Nanoscale, focused on cesium lead iodide (CsPbI₃) quantum dots, which exhibit promising optical and electronic properties but are inherently unstable at elevated temperatures.

The researchers employed two complementary strategies to tackle the issues. First, they replaced a small percentage of lead atoms in the crystal lattice with cobalt or silver. This lattice doping strengthened the material's structure and limited thermal expansion. Second, they passivated the quantum dots' surfaces with a mixture of chloride and iodide ions, reinforcing the surface and preventing defect formation.

When subjected to temperatures ranging from 20°C to 80°C, the untreated CsPbI₃ quantum dots showed signs of lattice distortion, emission quenching, and nonradiative energy loss above 60°C. In contrast, the cobalt- and silver-modified dots retained their cubic shape, exhibited less particle aggregation, and maintained stronger, better-defined light emission at higher temperatures.

Notably, the modifications expanded the material's thermal stability window by approximately 20°C. Moreover, the rise in thermally activated nonradiative recombination increased by less than 60% in the modified dots, compared to the untreated ones. Silver-doped quantum dots exhibited the greatest structural stability, with only about 0.6% lattice spacing expansion and minimal heat-induced narrowing of the electronic bandgap.

The combined approach effectively stabilized both the interior and surface of the quantum dots, suppressing the processes that typically reduce light emission under thermal stress.