High Efficiency Polymer-Titanium Oxide Hybrid Solar Cells

Increasing demands for highly efficient sources of renewable energy is motivating scientists to explore novel approaches. Polymer solar cells represent a promising route, but the efficiency in converting sunlight into useable electric power is still relatively low compared with inorganic technology based on silicon semiconductors. Recently we have demonstrated polymer tandem solar cells with a power conversion efficiency of 6.5%, with each layer processed from solution. A transparent TiOx layer is used to separate and connect the front cell and the back cell. The TiOx layer serves as an electron transport and collecting layer for the first cell and as a stable foundation that enables the fabrication of the second cell to complete the tandem cell architecture. We use an inverted structure with the low band-gap polymer/fullerene composite as the charge separating layer in the front cell and the high band-gap polymer composite as the charge separating layer in the back cell. We also believe that polymer tandem cells utilizing both new materials with tuned absorption spectra as well as high mobility and series stacking of the sub cells will yield results approaching 15% efficiency in the near future.