Highly Efficient and Stable White Light-Emitting Diodes Using Perovskite Quantum Dot Paper.

Chieh‐Yu Kang,Chih‐Hsiang Ho,Chun‐Ho Lin,Xuezhu Xu,Chin‐Wei Sher,Ting‐Zhu Wu,Sung‐Wen Huang Chen,Po‐Tsung Lee,Chih‐Hao Lin,Ting‐You Li,Hao‐Chung Kuo,Chun‐Lin Tsai,Maolin Zhang,Jr‐Hau He

doi:10.1002/advs.201902230

Abstract

Perovskite quantum dots (PQDs) are a competitive candidate for next‐generation display technologies as a result of their superior photoluminescence, narrow emission, high quantum yield, and color tunability. However, due to poor thermal resistance and instability under high energy radiation, most PQD‐based white light‐emitting diodes (LEDs) show only modest luminous efficiency of ≈50 lm W−1 and a short lifetime of <100 h. In this study, by incorporating cellulose nanocrystals, a new type of QD film is fabricated: CH3NH3PbBr3 PQD paper that features 91% optical absorption, intense green light emission (518 nm), and excellent stability attributed to the complexation effect between the nanocellulose and PQDs. The PQD paper is combined with red K2SiF6:Mn4+ phosphor and blue GaN LED chips to fabricate a high‐performance white LED demonstrating ultrahigh luminous efficiency (124 lm W−1), wide color gamut (123% of National Television System Committee), and long operation lifetime (240 h), which paves the way for advanced lighting technology.

Highlights

Both samples show strong diffraction peaks at 23°, which is caused by the CNC material; while the Perovskite quantum dots (PQDs) paper reveals other peaks appearing at 15°, 30°, and 34°, which we assigned to the (001), (200), and (210) crystal planes of the CH3NH3PbBr QDs,[32,33] confirming the high purity of the PQDs in the paper
The viewing angle of the light-emitting diodes (LEDs) can be further improved to 143° by using the flexible PQD paper as a curved color converter, illustrating the multifunctionality of the PQD paper
In remote-type design, the installation of PQD layer on top of the LED package can avoid the direct contact between PQDs and high-density heat inside the LED package, improving the stability and efficiency

Summary

Results and Discussion

The high-resolution XPS scans reveal the Br-3d, Pb-4f, and N-1s peaks, confirming the presence of PQDs. Generally, the Pb-4f peak of PQDs using ligand-assisted synthesis tends to shift to lower binding energy compared with normal bulk perovskite single crystals due to the interfacial electron transfer from electron-rich surface capping ligand to Pb2+ cation.[53,54,55] the CH3NH3PbBr3 PQDs based on cellulose-assisted growth demonstrate Pb-4f7/2 and Pb-4f5/2 peaks at 138.3 and 143.2 eV (Figure S8c, Supporting Information), which is lower than that of normal CH3NH3PbBr3 perovskites (around 138.8 and 143.7 eV),[55,56,57,58] implying that the complexation effect occurs between CNCs and PQDs. In addition, the gaps between individual CNCs can increase the heat dissipation area, which improves the thermal stability of the PQDs, leading to even better thermal resistance than state-of-the-art CdSe QDs (Figure S9, Supporting Information). In the design of a direct backlight system, using LEDs with larger viewing angles can increase the pitch between LEDs and decrease the optical distance, which means we can reduce the usage of LEDs and fabricate thinner backlight displays for future mini-LED backlight applications

Conclusion

Experimental Section

Conflict of Interest