Metal Halide Perovskite Light-Emitting Materials and Devices

Abstract

Metal halide perovskites were first rediscovered for photovoltaic applications in 2009. The performance of perovskite solar cells has undergone a rapid advancement with power conversion efficiency (PCE) increasing from 3.8% to over 25%, comparable to state-of-art commercial solar cells. Recent findings on excellent optoelectronic properties of perovskites like high photoluminescence quantum yield (PLQY), good charge transport and bandgap tunability motivate researchers to explore their applications in light-emitting devices such as light-emitting diodes (LEDs), multicolor displays and laser diodes. In this dissertation, I first introduce the development of perovskite LEDs (PeLEDs) and analyze key factors affecting the external quantum efficiency (EQE). The high refractive index of perovskites limits the light outcoupling efficiency to 20-25%. The next step to further increase EQEs should be focused on enhancing light extraction. Through an optical simulation, I found the emitter dipole orientation plays an important role. This finding may provide guidance on further performance boost of PeLEDs. CsPbI3 is the lowest bandgap all-inorganic perovskite, targeted for covering the red corner of CIE chromaticity diagram. However, CsPbI3 bulk films transition to undesirable orthorhombic phase at room temperature. CsPbI3 QDs are much more phase stable due to the reduced surface energy. Based on CsPbI3 QDs, I demonstrate a stable red-emission PeLED. To push perovskite materials towards commercialized display applications, I developed a high-resolution photolithographic approach to pattern multicolor perovskite thin films. This approach is based on a dry lift-off process, addressing the incompatibility of perovskites to common polar solvents. Using this approach, we fabricated a multicolor pixel array for liquid crystal displays (LCDs) and a prototype perovskite mirco-LED display. Besides great potential in display applications, perovskites have renewed people’s hope for achieving the long-standing goal of solution-processable electrically pumped laser diodes. I first demonstrate perovskite lasers integrated with distributed Bragg (DBR) and distributed feedback (DFB) cavities under optical pumping. Towards electrically pumped laser diodes, I suppressed the efficiency roll-off (droop) of perovskite LEDs by applying combined strategies. Finally, devices could be operated at high current densities up to 1 kA/cm2. Future work will be integrating DFB cavities with perovskite LEDs to approach the ultimate goal.