# Effects of Doped Hole-Transporting Layers on Perovskite Solar Cell Performances
## 3 Results and Discussion
Combining these electrostatic surface roughness and conductivity results, device performance enhancement was mainly caused by smoother surface formation and the conductivity increase through doping the HTL. Enhancement in the conductivity of PEDOT: PSS film was also proved by the increase in the charge transfer rate of the perovskite crystal to PRDOT: PSS. To evaluate the charge transfer from the perovskite layer to PEDOT: PSS film, fluorescence emission intensity was measured using a structure of ITO/PEDOT: PSS (with or without the solvent additive)/perovskite sample. As shown in Figure 5, a greater extent of fluorescence emission quenching (i.e., emission intensity decrease) was observed in the sample with DIO (device with microwave annealing showed higher emission quenching), indicating that the sample with the DIO additive exhibited a slightly higher quenching efficiency of excited states and a better hole transport ability than the device with bare PEDOT:PSS. Stability of the devices was tested using un-doped, DIO-doped, and DCO-doped PEDOT: PSS films by measuring the time required for the PCE to fall below 80% of the initial value (LT80). The PCE measurements were proceeded with at room temperature under ambient air conditions without device encapsulation. Figure 6 shows the PCE changes with time for these devices. The device with un-doped PEDOT: PSS film showed the LT80 of 20 h, while devices with both DIO- and DCO-doped PEDOT: PSS film showed the LT80 of about 90 h, which increased by 4.5 times compared with pristine device with un-doped PEDOT: PSS film. This enhancement in device stability resulted from the passivation effect of the bottom of the perovskite due to the additive alkyl di-halides [14]. DIO showed a slightly better LT80 between doping with DIO and DCO; the XRD intensity and AFM roughness values were also slightly better for DIO-doped devices, so all devices were prepared with DIO doping. Figure 5: Fluorescence emission spectra of the perovskite films deposited on bare PEDOT: PSS and DIO-doped PEDOT:PSS. When PEDOT: PSS nanoparticles are dispersed in distilled water, it takes a long time to anneal this spin-coated PEDOT: PSS hole-transporting layer (usually more than 10 min), which is another obstacle to the use of mass production methods such as roll-to-roll processing. A microwave annealing process was proceeded with using home-made power adjustable microwave equipment and compared with the conventional thermal annealing. The power of the microwave was set at 200 W (power of general microwave ovens is usually 800-1000 W) and the PEDOT: PSS film was annealed for 10 s, with a rest of 10 s, and annealed for another 10 s. The overall time required for microwave annealing was only 30 s, which is far less than that required for the conventional thermal annealing (typically 15 min in 120 \({}^{\circ}\)C oven). Table 3 summarizes the device performances according to annealing conditions. The PCE of the device fabricated on the un-doped PEDOT: PSS film with conventional thermal annealing was 13.20 \(\pm\) 0.31. While that for devices on 2 wt% DIO-doped PEDOT: PSS film was 14.42 \(\pm\) 0.39% for thermal annealing and 14.44 \(\pm\) 0.54 for microwave annealing. Doping HTLs increased the PCE of the device by about 10%. When comparing annealing conditions between the microwave and thermal annealing, all device parameters (i.e., Voc, Jsc, FF, and PCE) were quite similar; therefore, it could be concluded that microwave annealing could provide the same device performance while reducing the processing time by 1/30 th compared with thermal annealing. The effect of post-annealing was studied using a very weak power microwave. The conventional microwave power is too strong to the point that it cannot be used for fully fabricated devices (i.e., devices with metal electrodes) because of the reflection from the surface of the metal.