Blue Light-Emitting Semiconductor Based on Cesium Lead Bromide Perovskite Quantum Dots for Nano-Optoelectronics

Abstract

Currently, over 19% of the world's electrical energy is used for lighting, with a significant portion sourced from fossil fuels. This implies a great contribution to the depletion of finite resources and also contributes to carbon emissions, leading to adverse environmental effects such as global warming and environmental pollution. Therefore; exploring energy-efficient lighting and display technologies is crucial. Metal halide perovskites (MHPs) are among the promising candidates for next-generation solid-state lighting and display technology due to their exceptional optoelectronic properties. As a result, great achievements have been attended particularly in green and red light-emitting MHPs. However, unresolved issues with MHPs light emitters remain, particularly operational instability and low efficiency of blue-light emitters. Realizing these issues, we focused on the synthesis and characterizing of strongly quantum confined CsPbBr3 perovskite quantum dots (QD) as blue light-emitter. The formation mechanism of the CsPbBr3 nanocrystals (NCs) by supersaturated recrystallization at room temperature (SR-RT) was also elucidated. Finally, the properties of calcium (Ca) and/or strontium (Sr)-doped CsPbBr3 perovskite were investigated using density functional theory (DFT) calculations. We first synthesized blue light-emitting CsPbBr3 QDs with ZnBr2 using the SR RT synthesis method. The results from high-resolution transmission electron microscopy (HR-TEM) show that the synthesized QDs with ZnBr2 have an average size of ~3 nm. The X-ray diffraction (XRD) pattern of the CsPbBr3 QDs drop-cast film without and with ZnBr2 corresponds with the cubic phase of CsPbBr3. Even though, identifying doping sites is challenging, the energy dispersive spectroscopy (EDS) results suggest the presence of Zn2+ within the QDs. Ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence spectroscopy (PL) analysis confirmed that the synthesized QDs absorb and emit light in the blue-spectrum region. The bandgaps of CsPbBr3 QDs synthesized without and with ZnBr2 were determined to be 2.30 eV and 3.02 eV, respectively. In general, we anticipate that these approaches provide a new strategy for synthesizing strongly quantum-confined QD materials for photonic devices such as a light-emitting diode and lasers. xv Blue light-emitting CsPbBr3 NCs have currently received great attention due to their stability and efficiency. However, the control of CsPbBr3 NCs size within a strong quantum-confinement regime is challenging due to its fast nucleation and growth nature. Therefore, understanding the formation mechanism of these NCs could offer a reliable approach to control the size of CsPbBr3 NCs within a strong quantum confinement regime. Thus, we systematically studied the formation mechanism of CsPbBr3 NCs using SR-RT. Our investigation involved applying the LaMer model and Hansen solubility parameter analysis. We also demonstrate the entropy-driven mixing between two dissimilar polar-nonpolar (N, N-dimethylformamide (DMF)-toluene) solvents. Then, we find that in a poor solvent (toluene >> (DMF) in volume), ~60 nm sized CsPbBr3 NCs were synthesized via one step, whereas in a marginal solvent (toluene ≈ DMF), ~3.5 nm sized NCs were synthesized via two steps, indicating the importance of solvent polarity, specifically, solubility parameter. In addition, in the presence of CuBr2 additive, the high-quality cubic NCs (with ~3.8 nm and ~21.4 nm edge size) were synthesized. Hence, through this study, we suggest the ‘solubility parameter-based NC size control model’ for the SR-RT processes. Finally, we turned our focus to doping metal ions into CsPbBr3 perovskite. This method is effective for fine-tuning material properties, but choosing the right dopant is important. The toxicity of lead poses a significant challenge, along with the relatively low performance of blue lead halide perovskites. Therefore, substituting some Pb with less toxic elements presents an intriguing strategy. However, most materials tend to deteriorate properties of CsPbBr3 when doped in substantial amounts. In this study, structural, electronic, and optical properties of CsPb1-x-ySrxCayBr3 for (x=0, y=0; x=0, y=0.125; x=0.125, y=0 and x=0.125, y=0.125) perovskites calculated using density functional theory (DFT) as implemented in Quantum Espresso package. The result of calculation shows that the bandgaps of CsPb1-x-ySrxCayBr3 perovskites are 1.4, 1.68,1.74 and 2.33 eV for (x=0, y=0), (x=0, y=0.125), (x=0.125, y=0) and (x=0.125, y=0.125) respectively. However, the lattice parameters calculation for (x=0, y=0), (x=0, y=0.125), (x=0.125, y=0) and (x=0.125, y=0.125) are 5.87, 5.84, 5.87 and 5.85 nm respectively. Additionally, the density of states, electro-localization function, and optical properties were calculated. Therefore, our overall results suggest that Ca, Sr, and co- xvi doping in CsPbBr3 can be utilized for blue light-emitting diodes and other optoelectronic devices.