Figure 4. Photovoltaic and photostrictive properties of MAPbI₃ thin films.

(a) Typical current density–voltage characteristic of a MAPbI₃ thin-film photovoltaic cell (FTO/TiO₂/MAPbI₃/Spiro-OMeTAD/Ag) under simulated AM1.5 100 mW cm⁻² illumination (red line) and under dark (black line). The power conversion efficiency can reach 12.5%. The inset shows the SEM image of the MAPbI₃ thin film. The scale bar, 1 μm. (b) Height change of the MAPbI₃ thin film (4 μm) on FTO-coated glass substrate under illumination. The net response from the film can be obtained by substracting the extrinsic contribution from the substrate. Under 100 mW cm⁻² white light, about 5 nm height change can be observed, corresponding to a photostriction of 1,250 p.p.m.