# Effects of Doped Hole-Transporting Layers on Perovskite Solar Cell Performances
## 3 Results and Discussion  
The main target of this study is to enhance the performances of PSCs to be more realistic for their commercialization. A solvent additive-doped PEDOT: PSS was used as a hole-transporting layer of inverted type PSCs which is known as a favorable processing method to prepare large-scale PSCs because of the formation of a smooth surface and a more uniform perovskite layer through the electrostatic effect of the solvent additives contained in the PEDOT: PSS [17]. It is well known that the quality of perovskite grain growth is affected by the smoothness of the PEDOT: PSS layer [18; 19; 20]. DIO has been widely used as a surfactant in the organic solar cell industry to improve the morphology and control phase separation of two immiscible donor-acceptor materials. DIO has also been used as an additive for perovskite precursor solutions to improve the crystallinity of the perovskite crystal [21; 22]. The optimal solvent additive doping rate was obtained by changing the composition ratio of dopant DIO against PEDOT: PSS. Figure 1 shows the change in the open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and power conversion efficiency (PCE) according to the composition ratio of the additive. The device performances are summarized in Table 1. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**C (wt\%)** & **VOC (V)** & **JSC (mA/cm\({}^{2}\))** & **FF (\%)** & **PCE (\%)** \\ \hline
0 & 0.964 \(\pm\) 0.008 & 20.30 \(\pm\) 0.26 & 67.47 \(\pm\) 2.34 & 13.20 \(\pm\) 0.31 \\
1 & 0.971 \(\pm\) 0.010 & 20.35 \(\pm\) 0.67 & 67.93 \(\pm\) 1.57 & 13.42 \(\pm\) 0.60 \\
1.5 & 0.970 \(\pm\) 0.010 & 20.97 \(\pm\) 0.88 & 68.91 \(\pm\) 3.23 & 14.01 \(\pm\) 0.50 \\
2 & 0.991 \(\pm\) 0.024 & 21.04 \(\pm\) 0.86 & 69.20 \(\pm\) 0.97 & 14.42 \(\pm\) 0.39 \\
2.5 & 0.940 \(\pm\) 0.048 & 20.07 \(\pm\) 0.54 & 71.37 \(\pm\) 3.19 & 13.44 \(\pm\) 0.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Averaged device performances according to DIO doping concentrations. Figure 1: _Cont._All of the measured device performances were averaged over at least 10 devices. The best device performance was obtained with a 2 wt% doping ratio and the Voc, Jsc, FF, and PCEs of the PSC at AM 1.5 100 mW/cm\({}^{2}\) condition were 0.991 \(\pm\) 0.024 V, 21.04 \(\pm\) 0.86 mA/cm\({}^{2}\), 0.692 \(\pm\) 0.010, and 14.42 \(\pm\) 0.39%, respectively. Since the best device performance was obtained with a 2 wt% doping condition, all the other studies were processed using this doping ratio. The PCE of the device fabricated on the un-doped PEDOT: PSS layer with conventional thermal annealing was 13.20 \(\pm\) 0.31. Therefore, it can be concluded that doped PEDOT: PSS hole-transporting layer increased the PCE of the device by about 10%. To find out the electrostatic effect of a dopant (i.e., the surface ion density of the hole-transporting layer) on device performances, the solvent additive DIO was changed to 1,8-dichloroorotane (DCO). Since the electronegativity of chlorine atoms (3.16) is higher than that of iodine atoms (2.66), Pb\({}^{2+}\) ions included in perovskite crystal should be more strongly held through electrostatic interaction between chlorine atoms and lead ions. The devices  
Figure 1: Device parameters (Voc, Jsc, FF and PCE) as a function of solvent additive (DIO) composition. were prepared using the same method as for DIO; however, due to the molecular weight differences between iodide and chlorine (the molecular weight of DCO is 183.12 g/mol, while that for DIO is 366.02 g/mol) the same dopant mole ratio to PEDOT: PSS was reduced to 1 wt%. Table 2 summarizes the device performances with DCO as a dopant. Once again, the device doped with 1 wt% DCO showed the best device performances. The Voc, Jsc, FF, and PCE of PSCs at the AM 1.5 100 mW/cm\({}^{2}\) condition were 1.027 \(\pm\) 0.008 V, 20.68 \(\pm\) 0.62 mA/cm\({}^{2}\), 0.673 \(\pm\) 0.038, and 14.27 \(\pm\) 0.52%, respectively.