We show that electric force microscopy can be used to quantify light-induced electronic and ionic conductivity in thin-film perovskite samples. We use broadband local dielectric spectroscopy measurements to probe steady-state conductivity and use phase-kick electric force microscopy measurements to examine time-dependent conductivity. In a range of 3D lead halide perovskite semiconductors, we find that light appears to create ionic vacancies. In butylammonium lead iodide, BA2PbI4, a model 2D Ruddlesden--Popper perovskite semiconductor, light instead creates primarily electronic carriers. The 3D perovskites exhibited light-induced conductivity that decayed in 10 to 100 seconds, 109 slower than expected from direct electron-hole recombination. The relaxation was generally temperature dependent, with an activation energy of 0.5 eV. These observations suggest that light creates ionic carriers that subsequently recombine slowly in the dark. In one 3D perovskite alloy, FAMACs, the dark conductivity and the underlying activation energy for relaxation was furthermore found to be substrate dependent. This finding indicates that the electrical contact may have a large effect on perovskite electronic and ionic conductivity. The 2D perovskite's light-induced conductivity had a rise time and decay time of 100 microseconds, 104 slower than expected from direct electron-hole recombination and yet 105 faster than the conductivity recovery times seen in 3D lead halide perovskites. This observation suggests that the comparative stability of 2D perovskites may arise, in part, from a lack of light-induced vacancy formation.

Surprising light-induced electronic and ionic conductivity in 2D and 3D lead halide perovskite films revealed by electric force microscopy and accompanying theory

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