Fig. 3: Surface work function and ferroelectric effect of perovskite films.

a Secondary electron cut-off (SECO) and valence band maximum (VBM) of the UPS spectra for the control and DCl-treated perovskite films. b KPFM images of the (left) control and (right) DCl-treated perovskite films. c, d DFT-calculated electrostatic potential and surface work functions of perovskites without and with the adsorption of cage-like cations. e Charge density difference of perovskite with cage-like cations adsorption. Yellow iso-surface signifies electron accumulation, while blue represents electron depletion. PFM written-domains images of the (f) control and (g) DCl-treated perovskite films with ±10 V bias. h Phase distribution histogram of the control and DCl-treated perovskite films.