Interface engineering of layer-by-layer stacked graphene anodes for high-performance organic solar cells.

The major efforts in solar energy research are currently directed at developing cost-effective systems for energy conversion and storage. [ 1–3 ] The high cost of materials and preparation methods that are required for the fabrication of inorganic solar cells prevent their widespread deployment. Seeking a low-cost alternative in the form of solution-processable or roll-to-roll printable organic solar cells features prominently in the energy research roadmap. The conventional anode of choice for organic solar cells has been indium tin oxide (ITO), which consumes as much as 30% of the fabrication cost in solar cells. High quality ITO is expensive due to the dwindling supplies of indium. ITO also suffers from drawbacks like brittleness, sensitivity to acids and bases during processing, and reactive interface formation with copper indium sulfi de during high-temperature sintering. Graphene fi lms have been proposed as the new generation of multifunctional, transparent, and conducting electrodes. The attractiveness of graphene arises from their low cost, transparency, high electrical conductivity, chemical robustness, and fl exibility, as opposed to the rising cost and brittleness of ITO. [ 4–6 ]