Improving colour and efficiency in LEDs

Latest research into halide perovskites has demonstrated a way to achieve ultranarrow emission linewidths in solution-processed thin films, improving colour purity in perovskite LEDs across the blue-to-green spectrum.

The paper, published in Nature Synthesis, shows that narrower emission produces more saturated, precisely defined colours, which could lead to improvements in display technologies – such as televisions – where accurate colour reproduction and low energy loss are both key requirements.

The research, led by Jian Mao during a Marie Curie Fellowship in Professor Sam Stranks’s Optoelectronic Materials and Device Spectroscopy Group in the Department of Chemical Engineering and Biotechnology (CEB), addresses a long-standing challenge in perovskite LEDs. A key limitation in conventional perovskite thin films is inhomogeneous broadening, which is driven by variations in composition and crystal size across the film. This broadens the emission spectrum and reduces colour purity.

“Looking ahead, this research could help advance next-generation display technologies with more vivid colours and lower power consumption. It may also support the development of compact, low-cost and solution-processed light sources for optical communication, biological imaging and integrated photonic technologies,” Jian, now an Assistant Professor at Fudan University in China, said.

The team introduced an interface-regulated crystallisation approach to better control how the material forms during processing.

The method uses an underlying layer with minimal molecular interactions with perovskite precursors, with poly(9-vinylcarbazole) used as an example. This enables smoother ion diffusion during growth, and when combined with dimethylformamide vapour, promotes more controlled crystallisation.

The authors – including many colleagues from Professor Stranks’ research group – report that this leads to films with both horizontal and vertical homogeneity and reduced inhomogeneous broadening, approaching that of perovskite single crystals. This is reflected in ultranarrow photoluminescence linewidths of 13.6 nm, 13.7 nm, 13.8 nm and 14.4 nm across emission wavelengths from 464 nm to 522 nm.

When used in devices, the approach enables sky-blue perovskite LEDs with electroluminescence linewidths of 14.7 nm and a peak external quantum efficiency of 24.6%, with comparable performance across the blue-to-green emission range.