posted on 2024-02-05, 16:06authored byZehua Chen, Gaofeng Teng, Su-Huai Wei
The perovskite CsPbBr3 exhibits an unusual
nonmonotonic
dependence of the band gap on increasing pressure to about 2.0 GPa
as compared to conventional semiconductors. Using the first-principles
calculation method, we show that under pressure, isotropic volume
deformation induces considerable compression of the Pb–Br bond
length and thus an enhanced interaction between atomic orbitals of
the antibonding valence band maximum states and the mostly nonbonding
conduction band minimum states, resulting in a monotonic decrease
in the band gap. On the other hand, structural relaxation tends to
reduce the strain energy by decompressing the Pb–Br bond length
and simultaneously compressing the Pb–Br–Pb bond angle,
which increases the band gap energy. We find that the competition
between the volume deformation effect and structural relaxation effect
is the origin of the nonmonotonic behavior of the dependence of the
band gap on pressure.