100% internal quantum efficiency in polychiral single-walled carbon nanotube bulk heterojunction/silicon solar cells

Abstract

Bulk heterojunction films made of polychiral single-walled carbon nanotubes (SWCNTs) form efficient heterojunction solar cells with n-type crystalline silicon (n-Si), due to their superior electronic, optical, and electrical properties. The films are multi-functional, since their hierarchical surface morphology provides a biomimetical anti-reflective, air-stable, and hydrophobic encapsulation for Si. Also, the films have a large effective area conferring them high optical absorption, which actively contribute to the solar energy harvesting together with Si. Here, we report photovoltaic devices with photoconversion efficiency up to 12% and a record 100% internal quantum efficiency (IQE). Such unprecedented IQE value is truly remarkable and indicates that every absorbed photon from the device, at some wavelengths, generates a pair of separated charge carriers, which are collected at the electrodes. The SWCNT/Si devices favor high and broadband carrier photogeneration; charge dissociation of ultra-fast hot excitons; transport of electrons through n-Si and high-mobility holes through the SWCNT percolative network. Moreover, by varying the film thickness, it is possible to tailor the physical properties of such a two-dimensional interacting system, therefore the overall device features. These results not only pave the way for low-cost, high-efficient, and broadband photovoltaics, but also are promising for the development of generic SWCNT-based optoelectronic applications.