Electrical properties of bulk-heterojunction organic solar cells with ultrathin titania nanosheet blocking layer

摘要

The contributions of ultrathin titanium oxide nanosheet (TN) crystallites to the electrical properties and the diffusion of metal atoms were studied in a bulk-heterojunction (BHJ) cell in indium-tin oxide (ITO)/MoO_3/poly(3-hexylthiophene) (P3HT):phenyl-C_(61)-butyric acid methylester (PCBM) active layer/titania nanosheet (TN)/metal multilayered photovoltaic devices. The insertion of only two or three layers of poly(diallyldimethyl-ammonium chloride) (PDDA) and TN multilayered film prepared by the layer-by-layer deposition technique effectively decreased the leakage current and increased the open circuit voltage (V_(oc)), fill factor (FF), and power conversion efficiency (η) nearly two fold. Although the active layer has a hydrophobic surface, the active layer was fully covered by the insertion of only two or three layers of the PDDA/TN multilayered film and the ultrathin TN layer effectively prevented the metal atoms from diffusing into the polymer film. The impedance analysis and the cross-sectional transmission electron microscopy (TEM) images revealed that the TN layer effectively separated the organic layer/metal interface and blocked holes at the organic/TN interface resulting in the reduction in leakage current by nearly three orders of magnitude and the increase in the capacitance at a voltage around V_(oc).