Fig. 6

Chemical heterogeneity of CH₃NH₃PbI₃ on FTO/PEDOTS:PSS revealed by AFM-IR; a schematics of working principle, as detailed in ref. 45; b and c spectra of fresh and degraded sample; d and e chemical mapping of fresh and degraded sample at 1464 cm⁻¹, respectively. These data are unpublished. AFM-IR measurements were carried out on an Anasys Instruments nano-IR2 AFM equipped with one Daylight solutions pulsed QCL laser ranged from 1200–1700 cm⁻¹, using Anasys Instruments PR-EX-TnIR cantilever having spring constant of 2nN/nm. AFM topography was scanned firstly using tapping mode and then a serial of locations were selected for contact-mode AFM-IR spectrum measurement. The laser power was set as 3% and 270 kHz pulse rate were optimized to maximize the IR signal. After the local IR spectrum is collected, the wavelength is fixed at 1464 cm⁻¹, and then tapping AFM-IR image was collected at this wavelength to get the distribution of 1464 cm⁻¹ band. The fresh sample was prepared in advance according to ref. 17 and sealed in cell filled with N₂ protective atmosphere, and then taken out for immediate AFM-IR measurement; the degraded sample was exposed in air for 5 h before AFM-IR measurement