Methylammonium lead iodide perovskite can make high-efficiency solar cells, which also show an unexplained photocurrent hysteresis dependent on the device-poling history. Here we report quasielastic neutron scattering measurements showing that dipolar CH 3 NH 3 + ions reorientate between the faces, corners or edges of the pseudo-cubic lattice cages in CH 3 NH 3 PbI 3 crystals with a room temperature residence time of â 1/414â €‰ps. Free rotation, Ï €-flips and ionic diffusion are ruled out within a 1-200-ps time window. Monte Carlo simulations of interacting CH 3 NH 3 + dipoles realigning within a 3D lattice suggest that the scattering measurements may be explained by the stabilization of CH 3 NH 3 + in either antiferroelectric or ferroelectric domains. Collective realignment of CH 3 NH 3 + to screen a device's built-in potential could reduce photovoltaic performance. However, we estimate the timescale for a domain wall to traverse a typical device to be â 1/40.1-1â €‰ms, faster than most observed hysteresis.
Bibliographical noteFunding Information:
We thank Jean Marc Zanotti (LLB Saclay), Davide Moia and Nic Harrison for their useful discussions. P.R.F.B., A.M.A.L., B.C.O’R., J.N. and X.L. are grateful to the UK Engineering and Physical Sciences Research Council for financial support (grants EP/ J002305/1, EP/M023532/1, EP/I019278/1 and EP/M014797/1).
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)