A Helio Blog by Dr Bernard Wenger (CTO)

Colour conversion, the process of converting light of one wavelength to another, is increasingly being used in displays to improve brightness and colour purity whilst reducing power consumption. The materials that convert the colour need to emit light over a narrow wavelength range to achieve the maximum colour purity, and this is done in two fundamentally different ways depending on whether you are talking about quantum dots or perovskites.

With quantum dots, the colour is defined by strongly confining the excitation within very small nanocrystals. However, a very small variation in crystal size induces a significant colour change. For example, changing the size of a green InP quantum dot by plus or minus 1 nm shifts its colour to blue or orange respectively.

Perovskites are light emitting materials where the emission wavelength is defined by their chemical composition, that is by choosing and assembling the ions (charged atoms) that form the crystalline structure. Therefore, a large range of particle sizes can be tolerated before there is a significant change in output wavelength. This is a massive advantage when it comes to manufacturing perovskites compared with quantum dots which require sub-nanometer control of particle size. Colour by chemistry is also an advantage for thermal stability, as quantum dots vary in size with temperature causing an unwanted change in output wavelength.