The pristine PSC, PSC with nanopatterned TiO2 layer, PCBM-PSC and PCBM-PSC with nanopatterned TiO2 layer were fabricated and characterized by J-V curves, external quantum efficiency (EQE), integrated Jsc and transmittance measurement. The Jsc , Voc ,ff , and ECE of J-V curves were summarized in Table 2 . From the results obtained, the PSCs with nanopatterned TiO2 layer and PCBM-PSCs with nanopatterned TiO2 layer had better Jsccompared to the pristine PSCs and PCBM-PSCs, as shown in Figure 8 a, due to the improved electron generation through light harvesting on nanopatterned TiO2 layer.
As visualized in Figure 8b, the intensity of the pristine PSC is higher than other PSCs at the wavelengths below 350 nm. However, at wavelengths ranging from 350 nm to 800 nm, the intensity of the PCBM-PSC with nanopatterned TiO2 layer is the highest, indicating that more electrons were generated in the range of 350 nm to 800 nm.[14] Higher electron generation leads to a higher electron density, which increases the Jsc ,Voc and ff . Thus, the ECE of PSC will also increase. The integrated Jsc in Figure 8c can be calculated from Equation (1), in which F represents the Faraday constant, E is the solar spectral irradiance, and NA is the Avogadro constant. The integratedJsc matched with the measuredJsc of all four types of PSCs.
\(J_{sc,\ \ int}=\ \frac{F\ \times\ \int{\left(E_{\text{eλ\ }}\times EQE\right)\text{\ dλ}}}{N_{A}}\)(1)
The transmittance of pristine PSCs and PCBM-PSCs with nanopatterned TiO2 layer were measured by using UV-Vis spectrometer, as shown as in Figure 8d. Around 300 nm to 370 nm wavelengths, the transmittance of pristine PSC was higher than PCBM-PSC with nanopatterned TiO2 layer. On the contrary, for wavelengths higher than 370 nm, the transmittance of PCBM-PSC with nanopatterned TiO2 layer was higher than the pristine PSC. The transmittance enhancement was due to the rougher surface of PCBM-PSC with nanopatterned TiO2 layer compared to the pristine PSC, which might induces the changes in the refractive index.[14] Furthermore, if the angle of reflected-diffracted light is larger than the critical angle, it causes the total internal reflection because of the decrement in the refractive index values from the TiO2 to the air.[29] Thus, the lower the refractive index, the higher the transmittance.[30]
On top of that, the incorporation of PCBM into perovskite also contributed to Voc enhancement. This is becauseVoc is determined by the difference between the conduction band (CB) of electron transport material (ETM) and the valence band (VB) of perovskite, as shown in Figure 9 . Without PCBM, pristine PSCs and PSCs with nanopatterned TiO2layer have only one ETM, that is TiO2. However, with the incorporation of PCBM into perovskite, the PCBM-PSCs, and PCBM-PSCs with nanopatterned TiO2 layer have two ETMs, that are TiO2 and PCBM. Therefore, the CB of ETM will not depend only on the TiO2, but the average value between TiO2 and PCBM. In simpler words, it can be said that the CB of ETM were elevated by PCBM, which improvedVoc . As the difference between the CB of ETM and the VB of perovskite in PCBM-PSCs and PCBM-PSCs with nanopatterned TiO2 layer are higher than the pristine PSCs and PSCs with nanopatterned TiO2 layer, therefore theVoc of PCBM-PSCs and PCBM-PSCs with nanopatterned TiO2 layer are higher.