Influence of ZnO Content on Film Morphology and Device Performance of MEH-PPV/ZnO Hybrid Solar Cells

Abstract

Hybrid solar cells based on conjugated polymer poly(2-methoxy,5-(2’-ethylhexyloxy)-p-phenylene vinylene (MEH-PPV) and inorganic n-type zinc oxide (ZnO) nanoparticles were investigated. Polymer solar cells consisting of conducting polymer alone have low minority carrier mobility, for example, MEH-PPV has a high hole mobility but a low electron mobility. The intrinsic carrier mobility imbalance in the MEH-PPV severely limits the performance of pure polymer based solar cells. To overcome this imbalance, another material, i.e. n-type ZnO particles, is incorporated to act as an electron acceptor and a pathway for electron transport. In this experiment, as an active layer, ZnO nanoparticles synthesized in-house were blended with MEH-PPV purchased from Sigma-Aldrich. The front transparent conduction oxide (TCO) electrode used was commercial glass substrate coated with indium tin oxide (ITO) thin film. Blends of MEH-PPV with 0-30 wt% of ZnO in 1,2-dichlorobenzene were prepared and fabricated as active layers of the solar cells. The PEDOT:PSS and active layer were spin-coated onto ITO coated glass substrate. Aluminum was used for the top electrodes. The effects of ZnO solid content and film morphology on the performance of MEH-PPV:ZnO nanoparticle composite solar cells were investigated. Transmission electron microscopy (TEM) revealed that the ZnO nanoparticles consisted of a mixture of spherical and rod-like shapes. An increase in ZnO solid content resulted in an increase in size of the ZnO network. This was found to increase electron transport and, hence, improve solar cell performance.