Improved performance of organic solar cells by growth optimization of MoO3/CuI double-anode buffer

We investigated the effect of a CuI anode buffer layer (ABL) on the molecular orientation of the copper phthalocyanine (CuPc) in organic photovoltaic cells (OPV cells), and we compare it to the effect of MoO3 buffer layer. While, in the presence of CuI, the CuPc molecules lie down parallel to the substrate, they stand up perpendicular in the case of MoO3. We show that the optical absorption, the morphology, and the JV characteristics of the OPV cells depends strongly on the orientation of the CuPc molecules. The improvement of the OPV cells performance is related to the property modifications induced by the change in molecule orientation. We show that the improvement of the OPV cell performance through the templating effect of CuI depends strongly on the deposition rate of the CuI, because the CuI thin-film morphology depends on this deposition rate. In this context, we show that the use of a double-ABL MoO3/CuI leads to a significant improvement of the cell performance. These results are discussed on the basis of the dual function of MoO3 and CuI. While both of them reduce the hole-injection barrier, CuI improves the CuPc film absorbance through specific molecular order and MoO3 prevents the OPV cells from leakage-path formation.