Fig. 1. Schematic of structure. (a) Perovskite solar cell; (b) Spiro-OMeTAD molecule[17]

Fig. 2. Schematics of optical absorptance. (a) Ultraviolet-visible (UV-Vis) absorption of Spiro-OMeTAD films before and after oxidation; (b) calculation of total layer absorptance

Fig. 3. AFM of Spiro-OMeTAD film. (a) Before oxidation; (b) after oxidation

Fig. 4. Distribution of energy flow density inside devices. (a) Planar device without pinhole; (b) device with pinhole

Fig. 5. UPS spectra of Sprio-OMeTAD film before and after oxidation. (a) Spectrum of work function before oxidation; (b) spectrum of valence band after oxidation; (c) spectrum of work function after oxidation; (d) spectrum of valence band after oxidation

Fig. 6. Cross-sectional SEM image of perovskite solar cell

Fig. 7. EIS of four devices in dark state at 0.4-V bias voltage

Fig. 8. Devices obtained by four oxidation modes. (a) J-V curves; (b) EQE curves

Fig. 9. Statistical chart of PCE distributions of devices obtained by four oxidation modes