Fig. 9

Model for pulsed operation. a At zero bias in thermal equilibrium, the work function difference between the contacts causes ions in the perovskite to drift, screening the internal field in the device. In this diagram, the ionic charge depicted results from the net displacement of positively and negatively charged ion populations and is not meant to imply drift of individual ions from one interface to the other. b Applying a sudden forward voltage pulse (faster than the characteristic timescale of ion motion, τ_ion) tilts the overall band diagram accordingly, causing electrons and holes to accumulate near the emissive layer edges and recombine where the ionic defect concentration is highest. Photogenerated electrons and holes are swept to the emissive layer edges by the internal field and undergo similarly high non-radiative recombination. c Adding a small background bias can reverse the equilibrium ion drift, reducing the ion concentration near the edges of the perovskite and flattening its bands. d Applying a fast voltage pulse now leads to a more uniform distribution of injected electrons and holes and a lower concentration of ionic defects that act as non-radiative trap states in the recombination zone