Research On Performance Of ZnO Nanorods/MEH-PPV Bulk Heterojunction Solar Cells

Organic solar cells (OSCs) have attracted much attention in recent years, because of their light-weight, low-cost, easy fabrication, flexibility and large-area. However, the low power conversion efficiency (PCE) due to narrow absorption spectra and low carrier mobility of organic materials limits their practical application. To further improve the PCE, some researchers introduced high carrier mobility inorganic semiconductor nanocrystals into polymer solar cells. Inorganic nanocrystals are used as n-type semiconductor, and formed inter penetrating network with polymer materials to enhance the PCE of OSCs. In this thesis, we investigate ZnO nanoroods/MEH-PPV hybrid cells, and discuss the influence of device performance after adding different materials.Firstly, the structure and size of ZnO nanorods fabricated by a hydrothermal method are characterized by using X-ray power diffraction (XRD) and scanning electron microscope (SEM). We analyze the feasibility of ZnO nanorods used as the electron acceptor layer. Adding dye N719 can improve both the short-circuit current density (Jsc) and the open circuit voltage (Voc). LiF is used as anodic buffer layer in the device and the Jsc increases about 150% compared to that of device without LiF.Secondly, we choose a low energy gap polymer PPDIC and measure the electrical and optical properties of this new material, then mix it with MEH-PPV. The mixture is spin-coated on ZnO nanorods to fabricate solar cells. We find the proportion to form the best D/A inter penetrating network is 1:4. However, PPDIC has little solution to limit the performance of OSCs.Finally, the PTCDA layer is inserted between ZnO nanorods and MEH-PPV to improve the light absorption. After introducing PTCDA, the device shows a strong and broad absorption in visible region, which increases the number of photoinduced excitons, and thus results in an enlarged photocurrent. When the thickness of PTCDA is 40 nm, we can observe the smooth morphology of thin layer surface, and get the best performance of device.