Enhanced performance of inverted organic photovoltaic cells using CNTs-TiOX nanocomposites as electron injection layer

In this study, we fabricated inverted organic photovoltaic cells with the structure ITO/carbon nanotubes (CNTs)-TiOX/P3HT: PCBM/MoO3/Al by spin casting CNTs-TiOX nanocomposite (CNTs-TiOX) as the electron injection layer onto ITO/glass substrates. The power conversion efficiency (PCE) of the 0.1 wt% single-walled nanotubes (SWNTs)-TiOX nanocomposite device was almost doubled compared with the TiOX device, but with increasing concentration of the incorporated SWNTs in the TiOX film, the performance of the devices appeared to decrease rapidly. Devices with multi-walled NTs in the TiOX film have a similar trend. This phenomenon mainly depends on the inherent physical and chemical characteristics of CNTs such as their high surface area, their electron-accepting properties and their excellent carrier mobility. However, with increasing concentration of CNTs, CNTs-TiOX current leakage pathways emerged and also a recombination of charges at the interfaces. In addition, there was a significant discovery. The incorporated CNTs were highly conducive to enhancing the degree of crystallinity and the ordered arrangement of the P3HT in the active layers, due to the intermolecular pi-pi stacking interactions between CNTs and P3HT.