Simple O<sub>2</sub> Plasma-Processed V<sub>2</sub>O<sub>5</sub> as an Anode Buffer Layer for High-Performance Polymer Solar Cells

A simple O<sub>2</sub> plasma processing method for preparation of a vanadium oxide (V<sub>2</sub>O<sub>5</sub>) anode buffer layer on indium tin oxide (ITO)-coated glass for polymer solar cells (PSCs) is reported. The V<sub>2</sub>O<sub>5</sub> layer with high transmittance and good electrical and interfacial properties was prepared by spin coating a vanadium­(V) triisopropoxide oxide alcohol solution on ITO and then O<sub>2</sub> plasma treatment for 10 min [V<sub>2</sub>O<sub>5</sub> (O<sub>2</sub> plasma)]. PSCs based on P3HT:PC<sub>61</sub>BM and PBDTTT-C:PC<sub>71</sub>BM using V<sub>2</sub>O<sub>5</sub> (O<sub>2</sub> plasma) as an anode buffer layer show high power conversion efficiencies (PCEs) of 4.47 and 7.54%, respectively, under the illumination of AM 1.5G (100 mW/cm<sup>2</sup>). Compared to that of the control device with PBDTTT-C:PC<sub>71</sub>BM as the active layer and PEDOT:PSS (PCE of 6.52%) and thermally annealed V<sub>2</sub>O<sub>5</sub> (PCE of 6.27%) as the anode buffer layer, the PCE was improved by 15.6 and 20.2%, respectively, after the introduction of a V<sub>2</sub>O<sub>5</sub> (O<sub>2</sub> plasma) anode buffer layer. The improved PCE is ascribed to the greatly improved fill factor and enhanced short-circuit current density of the devices, which benefited from the change in the work function of V<sub>2</sub>O<sub>5</sub>, a surface with many dangling bonds for better interfacial contact, and the excellent charge transport property of the V<sub>2</sub>O<sub>5</sub> (O<sub>2</sub> plasma) layer. The results indicate that an O<sub>2</sub> plasma-processed V<sub>2</sub>O<sub>5</sub> film is an efficient and economical anode buffer layer for high-performance PSCs. It also provides an attractive choice for low-cost fabrication of organic electronics.