Rational Unraveling of Alkali Metal Concentration-Dependent
Photovoltaic Performance of Halide Perovskites: Octahedron Distortion
vs Surface Reconstruction
posted on 2022-01-05, 15:44authored byZhaobo Zhou, Ming-Gang Ju, Jinlan Wang
Adding alkali metal in organic–inorganic
halide perovskites
effectively improves its photovoltaic performance, while excessive
alkali metal incorporation would produce a detrimental effect. Through
density functional theory and nonadiabatic molecular dynamics simulations,
we demonstrate how and why the photogenerated carrier lifetime mutates
with the increase of alkali metal concentration. A small amount of
Rb doping in the lattice introduces a slight distortion of the octahedron,
reducing the overlap of frontier orbitals and decreasing the nonadiabatic
coupling, effectively enhancing the photogenerated carrier lifetime.
In contrast, excessive Rb will introduce defect states, resulting
in the low carrier lifetime by a factor of 2–3 orders of magnitude.
Strikingly, the surface formamidinium (FA) cations exhibit unexpected
responsibility for the carrier dynamics since its high-frequency thermal
vibration strongly leads to the ultrafast hole trapping and carrier
recombination. Our results provide new insight into the concentration-dependent
photovoltaic performance of alkali metal cations in organic–inorganic
halide perovskites.