Fig. 1. (Color online) Device structure and performance with different SnO₂ thickness. (a) The architecture of the device in this work. (b) J–V curves with different SnO₂ thickness. (c, d) The champion devices J–V and EQE curves with 30 nm SnO₂ buffer layer, respectively.

Fig. 2. (Color online) Device performance without the SnO₂ buffer layer and with 30 nm SnO₂ buffer layer. (a) TRPL curves of the devices. (b) R_sh of the devices. (c)J–V curves of the devices under dark condition. (d) Fitting curves for calculation the n and J₀ from the darkJ–V data.

Fig. 3. (Color online) Top view SEM of SnO₂ layer with various thicknesses based on the structure of ITO/PTAA/Perovskite/PCBM. (a), (b), (c), (d) and (e) with thickness of SnO₂ of 0, 10, 20, 30 and 40 nm, respectively. (f) With a larger magnification to show a clearer morphology of SnO₂ with the thickness of 30 nm. (g) RMS of the films with different thicknesses of SnO₂. (h) The schematic diagram of the sample with a thinner BCP layer. (i) The schematic diagram of the sample with a BCP and SnO₂ bilayer.

Fig. 4. (Color online) (a, b) The water contact angle of the device without and with SnO₂. (c–f) NormalizedV_OC, J_SC, FF and PCE of perovskite devices without and with 30 nm SnO₂ kept in the atmosphere (25 °C, 20–40 RH%) without encapsulation for 600 h, respectively.