A PCBM-Modified TiO₂ Blocking Layer towards Efficient Perovskite Solar Cells

Figure 4

AFM photographs of TiO₂ thin films prepared at (a) 2000 rpm, (b) 4000 rpm, and (c) 6000 rpm, respectively. The root mean square roughness (RMS) value of TiO₂ thin films prepared at 2000, 4000, and 6000 rpm was 10.4 nm, 13.2 nm, and 18.4 nm, respectively. AFM photograph of TiO2/PCBM thin films with TiO₂ prepared at 4000 rpm and PCBM at (d) 2000 rpm, (e) 4000 rpm, and (f) 6000 rpm, respectively. RMS roughness for (d) is 15.6 nm, (e) is 15.3 nm, and (f) is 16.0 nm. AFM photographs of CH₃NH₃PbI_3−xCl_x organometal halide perovskite material, with a constant spin coating speed of TiO₂ at 4000 rpm and PCBM at (g) 2000 rpm, (h) 4000 rpm, and (i) 6000 rpm, respectively. RMS roughness for (g) is 15.6 nm, (h) is 13.8 nm, and (i) is 12.2 nm.

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