# Effects of Doped Hole-Transporting Layers on Perovskite Solar Cell Performances
## 3 Results and Discussion
The PCEs of the devices doped with DIO and DCO were within the experimental error range, so it could be concluded that the electrostatic effect of the dopant on the device performance was very weak. The surface roughness effect on the device performances was tested by preparing three different hole-transporting layers (un-doped PEDOT: PSS film, DIO-doped PEDOT: PSS film, and DCO-doped PEDOT: PSS film). Perovskite film was fabricated on these hole-transporting layers by the one-step method explained in the \"Experiment\" section. Figure 2 shows AFM topology images of the perovskite grain fabricated on these hole-transporting layers. The rms (root mean square) roughness values were 17.15 nm, 10.83 nm and 13.59 nm, respectively. The surface roughness was lowest for the perovskite film coated on the DIO-doped PEDOT: PSS layer. Since the perovskite film was formed on the PEDOT: PSS layer, it was concluded that the smoother the PEDOT: PSS film was the smoother the perovskite film also was. To study the effect of doping on perovskite crystallinity, X-ray diffraction (XRD) analysis was proceeded with. Figure 3 shows the XRD images of the film formed on the three different hole-transporting layers. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**C (wt\%)** & **V\({}_{\text{OC}}\) (V)** & **Jsc (mA/cm\({}^{2}\))** & **FF (\%)** & **PCE (\%)** \\ \hline
0 & 1.023 \(\pm\)  
Diffraction peaks appeared at 20 = 14, 28, and 32\({}^{\circ}\), which assign to the (110), (220), and (310) planes of the tetragonal CH\({}_{3}\)NH\({}_{3}\)PbI\({}_{3}\) perovskite structures [23]. Compared with XRD peak intensity, it was clear that the crystallinity of perovskite films formed on the doped hole-transporting films (both DIO and DCO) were higher. The surface roughness effect on the device performances was studied by forming devices on these three different hole-transporting layers. The external quantum efficiency (EQE) measurement, as shown in Figure 4, confirms the higher photon absorption in the range of 350-800 nm for the PSCs with additives compared with that for the PSCs without additives. Figure 3: (a) XRD images for the three different hole-transporting layers and (**b**) the plane diffraction peak intensity ratio of each layer. The integral current density of the EQE spectra over the AM 1.5G solar emission spectrum shows values over 20 mA/cm\({}^{2}\) for the device with additives and about 18 mA/cm\({}^{2}\) for the device without additives. The trend of EQE spectra was consistent with the results of the I-V curve. The PCE of the device formed on the doped hole-transporting films (both DIO and DCO) showed about 10% enhanced efficiency compared with that formed on un-doped hole-transporting films (Tables 1 and 2). This increase is exactly the same amount as that of the increase in the PCE through the surface smoothness effect due to doping the PEDOT: PSS layer and it confirmed that there was no electrostatic effect contribution. To analyze the doping effect on the conductivity of the PEDOT: PSS layer, the sheet resistance was measured using four probe methods [24]. The sheet resistances of un-doped PEDOT: PSS film, DIO-doped PEDOT: PSS film, DCO-doped PEDOT: PSS film coated on ITO glass were 181.8, 161.4, and 163.6 \(\Omega\), respectively. The thickness of the film that was  
Figure 4: J-V curves and external quantum efficiency of the devices. required to obtain this sheet resistance was measured using SEM, which turned out to be 30.6 nm. The final conductivity of un-doped PEDOT: PSS film, DIO-doped PEDOT: PSS film, DCO doped PEDOT: PSS film were 1796, 2023, 1996 S/cm, respectively. The solvent additive doping of PEDOT: PSS increased the conductivity of PEDOT: PSS film. The conductivity of both DIO- and DCO-doped PEDOT: PSS film was within the experimental error range, so it could be concluded that the conductivity of these doped PEDOT: PSS films was same.