Bandgap Engineering of Cesium Lead Halide Perovskite CsPbBr₃ through Cu Doping

Abstract

Cu-doped CsPbBr 3 with strong blue emissions is a potentially ideal material for high-quality light-emitting diode (LED) devices. This study thoroughly analyzes the influence of a Cu dopant on CsPbBr 3 materials through a series of theoretical investigations. Two artificial CsPbBr 3 supercells are constructed, and their electronic properties are analyzed. Additionally, the antibonding nature of the conduction band minimum (CBM) and valance band maximum (VBM) of CsPbBr 3 is elucidated. The results indicate that a Cu dopant can only alter the local lattice around it, not the entire lattice. Moreover, the CBM and VBM deformation potentials of CsPbBr 3 behave differently. Therefore, the energetic shift of VBM is more sensitive to the shrinkage of lattice due to the smaller energy difference between the constituent orbitals, leading to a bandgap reduction with the lattice contraction. This study reveals that the two critical reasons for the increase of bandgap are the contribution of Cu-3d orbitals to the VBM and the localized lattice distortion caused by Cu impurity. Therefore, this work clarifies how Cu impurities improve the blue light emitting performance of CsPbBr 3 systems.

Investigation on the Cu-Dopant-Induced Modulation Effect on the Optoelectronic Efficiency and the Stability of CsPbBr3 Perovskites

“…Specifically, the introduction of Cu doping results in a more compact CsPbBr 3 lattice with strengthened bonds, reducing the likelihood of intrinsic defects forming. This increases in the co-ordination number of cations and improved lattice order, which aligns with previous experimental observations [23].…”

“…Bi et al have experimentally demonstrated that substituting Cu for Pb in CsPbX 3 perovskites enhances the PLQY from 23% to an impressive value of 80%. Furthermore, this high PLQY can be sustained for 30 days under 60% relative humidity [22,23].…”

“…The introduction of the Cu dopant resulted in a reduction of the lattice parameters of CsPbBr 3 to a = 16.35 Å, b = 8.41 Å, and c = 11.79 Å, due to the smaller radius of the Cu ion. According to the X-ray diffraction (XRD) pattern analysis in Figure 2 provided by Bi et al [23], it is evident that the diffraction peaks shift towards higher angles (increased 2θ values), and the positions of peaks at larger 2θ values also increase. This observation suggests a decrease in the interplanar spacing of the crystal, providing experimental confirmation of the conclusion that the lattice constant is reduced.…”

Studies on the Light-Induced Phase Transition of CsPbBr3 Metal Halide Perovskite Materials

“…This enhances the s-p orbital coupling between Pb and Br atoms, so both VBM and CBM (all antibonding states) shift upward. The volume deformation potentials are often used to express the relationship between the volume change and the shift of band edge, which is inversely proportional to the energy difference between the two atomic orbitals of bonding interactions . The energy difference between Br–4p and Pb–6s is lower than that between Br–4s and Pb–6p, so the VBM has a higher volume deformation potential than the CBM.…”

“…The volume deformation potentials are often used to express the relationship between the volume change and the shift of band edge, which is inversely proportional to the energy difference between the two atomic orbitals of bonding interactions. 42 The energy difference between Br−4p and Pb−6s is lower than that between Br−4s and Pb−6p, so the VBM has a higher volume deformation potential than the CBM. Namely, the VBM is more sensitive to changes of the coupling interactions and shift with a higher value, so to reduce bandgap.…”