Polymer-doped perovskite nanocrystals for efficient single active layer white light-emitting diodes through energy transfer

White-light emitting diodes (WLEDs) are mainly constructed by stacking different light-emitting layers with complementary emission spectra. However, this not only requires complex device fabrication processes but also needs comprehensive charge transport regulation, limiting the development and application of WLEDs. In this work, efficient single-layer WLEDs are achieved via doping tiny amount of a red polymer poly[[9-(1-octylnonyl)- 9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5 thiophenediy (PCDTBT8) into the perovskite nanocrystals (NCs) matrix. The 490 nm sky blue perovskite nanocrystals (FA0.08Cs0.92PbBr2Cl) are synthesized and passivated with a short-chain ligand 3-methoxyphenethylamine (MPEA), which enhances luminance and stability at high bias. Energy transfer from NCs to PCDTBT8 significantly enhances red-light emitting in the range from 600 to 750 nm, enabling white-light emission. By tuning of the NCs:PCDTBT8 weight ratio from 400:1 to 150:1, a continuous transition of emission from cold white-light to warm white-light is achieved. With the NCs:PCDTBT8 weight ratio of 250:1, a standard white-light emission with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.33), a luminance of 752 cd/m2 and an external quantum efficiency (EQE) of 1.59% are obtained at a fairly low voltage of 4.8 V.