Figure 7. FTIR of a) FTO, b) perovskite/FTO, c) PCBM/FTO, and d) PCBM-perovskite/FTO.
To elaborate on the information of the PCBM-perovskite layer, FTIR spectroscopy was carried out and the results are as shown as inFigure 7. Figure 7 shows the comparison between the FT-IR spectra of a) FTO, b) perovskite/FTO, c) PCBM/FTO, and d) PCBM-perovskite/FTO. The peaks at 3200 and 3100 cm-1are due to the N-H stretching vibration for primary amines, and the 1600 and 1475 cm-1 double bands belong to the C=C group. The C-N stretching absorption that occurs in the region from 1250-1000 cm-1 indicates the aliphatic amines[26] while the single band at 900 cm-1 is corresponding to the metal iodide stretching vibration,[27] as shown in Figure 7b.
Apart from that, the incorporation of PCBM in the PCBM-perovskite layer was confirmed by comparing Figure 7c and 7d. The absorption bands for PCBM can be observed near 3000 cm-1, which indicates the sp3 C-H absorption of alkanes group while the absorption bands for C=O and C-O that appear within the range of 1750-1735 and 1300-1000 cm-1 indicate that the compound is an ester. The peak at 1465 cm-1 is due to the CH2 bending absorption, which is the characteristic of methylene group[26] and the peak at 524 cm-1 belongs to C60.[28] It can be seen that the main characteristic peaks of perovskite and PCBM can be identified in Figure 7d, which indicate the good formation of the PCBM-perovskite layer.