| 초록 |
Several metallic elements and compounds (LiF,Ca,Mg,TiOx,ZnO) are known for n-type buffer layers to improve power conversion efficiencies(PCE) in organic photovoltaic cells(OPVs). Ytterbium (Yb) also functions as n-type buffer layer in OPVs, although it is not well known to be applied in organic devices. Here we report how Yb functions as an n-type buffer layer especially in inverted structured OPVs. We observed Yb is more efficient to improve PCE in inverted structured OPVs than other materials. The trend demonstrates that Yb works to low work function of ITO, which acts as a cathode by ultraviolet photoemission spectroscopy (UPS) analysis. From the measurements of impedance spectroscopy and current-voltage curve, parameters to determine the performance of OPVs are analyzed. The results indicate that the main factor to make OPVs with Yb superior to other materials is fill factor (FF) which mostly stems from the low series resistance. |
