Effect of Interface Thickness on Power Conversion Efficiency of Polymer Photovoltaic Cells

We investigated the effect of the thicknesses of the interface layers (here, PEDOT:PSS and LiF) of polymer photovoltaic cells because variations in thickness strongly affect the power conversion efficiency (PCE). It was observed that the PCE rapidly increased with a PEDOT:PSS thickness of up to similar to 2,000 rpm and rapidly decreased when the PEDOT:PSS was thicker than similar to 2,000 rpm. A PCE of 6.648% was obtained at a specific PEDOT:PSS layer thickness of similar to 2,000 rpm, about 41.5% (from 4.698 to 6.648%) higher than the PCE with no PEDOT:PSS layer. In addition, the PCE slightly increased with an LiF layer thickness of up to similar to 0.5 nm and rapidly decreased when the LiF layer was thicker than similar to 0.5 nm. The maximum PCE was obtained at the LiF layer thickness of similar to 0.5 nm. In particular, the maximum values of PCE, J(sc), V-oc, and FF were obtained at 6.827%, 15.74 mA/cm(2), 0.665 V, and 0.652, respectively. The PCE increased 209.2% (from 2.028 to 6.827%), compared to the LiF layer thickness of similar to 5 nm.