Impact of Small Phonon Energies on the Charge-Carrier Lifetimes in Metal-Halide Perovskites

Abstract

Metal-halide perovskite (MHP) solar cells exhibit long nonradiative lifetimes as a crucial feature enabling high efficiencies. Long nonradiative lifetimes occur if the transfer of electronic into vibrational energy is slow due to, e.g., a low trap density, weak electron-phonon coupling, or the requirement to release many phonons in the electronic transition. Here, we combine known material properties of MHPs with basic models for electron-phonon coupling and multiphonon-transition rates in polar semiconductors. We find that the low phonon energies of MAPbI lead to a strong dependence of recombination rates on trap position, which we deduce from the underlying physical effects determining nonradiative transitions. This is important for nonradiative recombination in MHPs, as it implies that they are rather insensitive to defects that are not at midgap energy, which can lead to long lifetimes. Therefore, the low phonon energies of MHPs are likely an important factor for their optoelectronic performance.

What Makes a Good Solar Cell?

“…We use Equation with a τ 0 chosen based on ref. and a completely arbitrarily chosen trap density of N t = 10 15 cm −3 . We use an effective mass m eff = m and a relative permittivity of ε r = 10 for the calculations.…”

Key Tradeoffs Limiting the Performance of Organic Photovoltaics

“…However, it is also relevant to semiconductors. As has been discussed in the context of hybrid organic–inorganic perovskites, it explains why traps constitute efficient recombination centers . Since these are lower in energy, fewer phonons are required.…”

Breakdown of the Static Picture of Defect Energetics in Halide Perovskites: The Case of the Br Vacancy in CsPbBr3

“…[13][14][15][16] This suggests that electronic defect states in these materials are unusually benign electrically. 10,[17][18][19][20][21] Therefore, there are significant and on-going efforts to understand defect energetics and its relation to charge carrier scattering and recombination in HaP materials.…”