Abstract

Bulk heterojunction solar cells based on an organic donor that generates excitons upon photo irradiation and an organic/ inorganic acceptor is widely regarded as a potential route towards efficient, low cost renewable energy source that can be printed onto flexible substrates. Over the past decade, embedding of carbon nanotubes into organic solar cells has been an area of intensive investigation. The role of carbon nanotubes in such photovoltaic systems have been investigated for a variety of applications ranging from transparent electrodes, transparent and conductive hole or electron extraction layers, electron acceptors as well as additional exciton dissociation sites. In this work, we demonstrate the use of polymer wrapped semiconducting single walled carbon nanotubes (s-SWNTs) with a transmission of 89% at 550 nm as efficient hole extraction layers in organic photovoltaics based on a device architecture consisting of PTB7 /PC70BM as the active layer. We report the highest reported power conversion efficiency (PCE) of a carbon nanotube incorporated organic solar cell with an efficiency of 7.6%. The effectiveness of the nanohybrid hole transport layer is further proven by the low PCE of 5.6% for the reference device which does not consist of a hole extraction layer. This enhancement is mainly governed by the 32% increase in fill factor compared to the reference device without a hole transport layer.