# Effects of Doped Hole-Transporting Layers on Perovskite Solar Cell Performances
## 3 Results and Discussion
In this post-annealing study, the power of the microwave was set at 50 W to penetrate through the metal electrode and to vaporize any trace of moisture contained inside of the device during the fabrication processes. The fully fabricated devices were exposed to microwaves for only 5 s. The PCE was measured before and after \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Conditions** & **VOC (V)** & **JSc (mA/cm\({}^{2}\))** & **FF (\%)** & **PCE (\%)** \\ \hline Thermal, undoped & 0.964 \(\pm\) 0.008 & 20.30 \(\pm\) 0.26 & 67.47 \(\pm\) 2.34 & 13.20 \(\pm\) 0.31 \\ Thermal, 2 wt\% DIO & 0.991 \(\pm\) 0.024 & 21.04 \(\pm\) 0.86 & 69.20 \(\pm\) 0.97 & 14.42 \(\pm\) 0.39 \\ Microwave, 2 wt\% DIO & 0.988 \(\pm\) 0.019 & 20.64 \(\pm\) 1.09 & 70.91 \(\pm\) 2.83 & 14.44 \(\pm\) 0.54 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Device performances according to the annealing method. Figure 6: PCE changes of the devices with un-doped, DIO-doped, and DCO-doped PEDOT: PSS films as a function of time at 35% relative humidity condition without encapsulation. microwave treatment. The fabricated devices were stored at an ambient condition with a relative humidity of 35% without device encapsulation. Table 4 summarizes the PCE changes as a function of time. Both un-doped and doped devices showed enhanced PCE after microwave treatment. The un-doped device failed one day after fabrication, while the DIO-doped device survived for 5 days and showed enhanced PCE after microwave treatment. From these results, it could be concluded that a low power microwave treatment could vaporize traces of moisture and prolong the lifetime of the device. To more effectively check the effect of doping on increasing the stability and lifetime of the devices, the active area was doubled in width and length. The area of the cell was increased from 0.09 cm\({}^{2}\) to 0.36 cm\({}^{2}\). Table 5 summarizes the best PCE of small and large-area device with different conditions. The PCE of thermally annealed un-doped cells with an area of 0.09 cm\({}^{2}\) was 13.62%, while that of such cells with an area of 0.36 cm\({}^{2}\) was 9.96%. The PCE of thermally annealed 2 wt% DIO-doped cells with an area of 0.09 cm\({}^{2}\) was 15.03%, while that of such cells with an area of 0.36 cm\({}^{2}\) was 12.15%. The PCE of a larger area cell was reduced less (about a 27% reduction for un-doped cell sand about a 19% reduction for un-doped cell) for DIO-doped cells, probably due to the better areal uniformity caused by a smoother hole-transport layer through doping the PEDOT: PSS layer. The PCE of microwave annealed 2 wt% DIO-doped cells with an area of 0.09 cm\({}^{2}\) was 14.96%, while that of such cells with an area of 0.36 cm\({}^{2}\) was 12.21%. The PCE drop of larger area cells was about 18% for this microwave annealing condition. Once again, the microwave annealing did not affect the device performance even for larger area cells, it could only reduce the time required for annealing to 1/30 th compared with that of thermal annealing. Long-term stability of the larger area device was also studied. The time required for LT80 conditions was measured while the devices were exposure to 100 mW/cm\({}^{2}\) of solar simulator light at a relative humidity of 35% without device encapsulation (Figure 7a,b). Figure 7a shows the 0.09 cm\({}^{2}\) cell data whereby the LT80 for an un-doped cell was 3.4 h and that for a 2 wt% DIO-doped cell was 5.3 h. The lifetime of doped devices was enhanced by about 1.6 times compared with that for un-doped devices. Figure 7b shows the 0.36 cm\({}^{2}\) cell data whereby the LT80 for an un-doped cell was 2.7 h and that for a 2 wt% DIO-doped cell was 4.9 h. The lifetime of doped, larger-size devices was enhanced by about 1.8 times compare to that for un-doped devices. Even though the absolute value of the LT80 for larger-size cell decreased as the cell area increased (i.e., in the case of doped cells, 5.3 h