© Fraunhofer IAP
© Fraunhofer IAP

Cadmium-free quantum dots for QLEDS and solar cells

Cadmium-free quantum dots for QLEDS and solar cells

Quantum dots (QD) are a new class of fluorescent nanomaterials. Tiny nanocrystals enable them to efficiently produce astoundingly brilliant colors. Their absorption and emission properties can be customized in a unique way by changing the particle size. Modifying the surface of the particle tailors it to its chemical environment. Virtually the entire spectral range is accessible through targeted synthesis. These extraordinary properties enable them to be used in a wide range of applications, for example, as a luminescent material, in display technology, for up-conversion in photovoltaics and as a security feature on banknotes.

Conventional QDs, however, contain the toxic heavy metal cadmium. In response, the Fraunhofer IAP is developing the synthesis of cadmium-free quantum dots. These are indium phosphide-based (InP/ZnS-multishell QDs) and environmentally friendly. They can be used as a fluorescent material for LEDs, as an emitter material in OLEDs, or as a filter for the LED backlighting of LCDs which produces a higher color brilliance on the LCD display. Infrared active copper indium sulfide QDs (CuInS2-QDs) can also increase the efficiency of solar cells.

Compared to conventional QDs, cadmium-free materials from the Fraunhofer IAP also achieve high quantum yields. Up to several grams of cadmium-free QDs can be produced per hour with the aid of a flow-through reactor that is continuously operational. Like the ink in the ink-jet process, they can be printed onto firm and flexible substrates. To do this, a pilot plant producing OLEDs and solar cells is located at the Fraunhofer IAP.