서강대학교

초록/요약

We study the thermal annealing effect on phase separation morphology in thin films of polyfluorene polymer blends. They consist of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)] (TFB) by varying weight ratio. F8BT:TFB blend PEDOT:PSS/SiO2/Si and Ag/V2O5/F8BT:TFB blend/ZnO/ITO are prepared to measure structural morphology and device performance, respectively. Prior studies revealed that F8BT has high electron mobility and TFB has high hole mobility. However, device performance whose active layer consists of these two polymers is not yet revealed. In this study, we employ grazing incidence wide angle X-ray scattering, X-ray reflectivity, and atomic force microscope to measure morphology change in vertical and lateral direction. To compare the device efficiency and performance, each sample was measured UV-visible spectra and I-V curve with solar simulator. We found that the blend of F8BT and TFB does not show clear evidence of crystallinity and ordering. Given that increasing annealing temperature makes F8BT crystallized, it is due to the regioregularity of TFB. With increasing annealing temperature, we also found that F8BT:TFB blend ratio of 2:1 shows enhancement of fill factor and power conversion efficiency at 160℃ whereas 1:2 and 1:1 shows degradation of devices. This degradation might be due to aggregated polymer domain structure and decrease of interfacial area between F8BT and TFB preventing exciton diffusion difficult. This study gives insight for all-polymer solar cells producing the more efficient device in terms of morphology and thermal annealing.