Chapter 11 - Organic Solar Cells Enhanced by Carbon Nanotubes

Abstract

This chapter discusses carbon nanotube-enhanced organic solar cells with bulk heterojunctions. It has been found that the performance of organic bulk heterojunction solar cells can be significantly increased by introducing carbon nanotubes into the active layer. Carbon nanotubes (CNTs) have been widely used in different aspects of photovoltaics. First, CNTs could be a good replacement for indium tin oxide as the transparent electrode of solar cell devices; second, the multiple exciton generation in CNTs, arising from the quantum confinement effect in the low-dimensional materials, could increase the internal quantum efficiency and hence the short circuit current in CNT-based solar cells; third, introduction of CNTs in solar cells could increase the carrier mobility because CNTs can provide a ballistic pathway for a photoexcited carrier to transport. The Kelvin probe force microscopy study suggests that the increased performance is due to increased hole mobility as carbon nanotubes are donor materials. However, it has also been found that excessive carbon nanotubes degrade the performance of organic solar cells because of the increased bimolecular recombination due to the existence of metallic CNTs. Therefore, it is critical to find new ways to fabricate pure semiconductor CNTs for enhancing the performance of OSCs with bulk heterojunctions.