Nano-engineering of hybrid organic heterojunctions with carbon nanotubes to improve photovoltaic performance

Organic-inorganic hybrid photovoltaics are beginning to show significant promise as a low cost highly efficient route towards renewable energy generation. Of the hybrid architectures available, carbon nanotube incorporated organic photovoltaics is considered to be among the most promising. Herein, the optical and electronic effects of localizing multiwalled carbon nanotubes in the donor polymer is investigated in comparison to its incorporation into the bulk heterojunction architecture (triple heterojunction scheme) through photoluminescence quenching and dark diode characteristics analysis. A significant improvement in photoluminescence quenching is observed when the nanotubes are localized in the donor polymer where the active layer is formed through a sequential deposition route in comparison to the triple heterojunction scheme. However, the former architecture also leads to a higher recombination of carriers due to the introduction of trap states as observed through space charge limited conduction analysis. In comparison, the triple heterojunction scheme shows a lower dark current and hence a significantly improved photovoltaic device performance (3.8% in comparison to 2.6% for the sequentially deposited architecture). This indicates that the formation of the triple heterojunction is the more ideal scheme for improving device performances in organic-inorganic hybrid architectures