fig4

Figure 4. (A) Variations of the UV-vis absorption and (B) XRD measurement of perovskite without and with PI under an RH of 75% at 25 °C in dark conditions with respect to the exposure duration. (C) Long-term stability of the six corresponding PSCs under an RH of 50% at 25 °C in dark conditions. The inserts are optical photographs. (D) Normalized average PCE of 10 PSCs as a function of stretching cycles under a curvature radius of 6.25 mm. The inset shows the photograph of the flexible device under curvature. XRD: X-ray diffraction RH: relative humidity; PSCs: perovskite solar cells; PI: polyimide.