Conformal coating of titanium suboxide on carbon nanotube networks by atomic layer deposition for inverted organic photovoltaic cells

Abstract

We propose a new strategy for improving the charge selectivity of carbon nanotubes (CNTs) for organic photovoltaic cells (OPVCs). The strategy involves the coating of an ultrathin layer of titanium suboxide (TiOx) on CNTs by atomic layer deposition (ALD). ALD can facilitate that conformal and uniform coating of TiOx on CNT networks while preserving their nanoporous structure. We used the TiOx-coated CNT networks as an electron transport layer in inverted OPVCs. TiOx-coated CNTs can provide electrons with an extremely fast conductive path through CNTs and selectively block the holes by means of the hole-barrier property of the TiOx in OPVCs. The nanoporous structure of TiOx-coated CNT networks can improve the device performance of OPVCs due to synergetic effects of the electron selective transport property of TiOx and the high conductivity of CNTs. In addition, further improvement of device performance can be achieved by adding a hole transport layer (MoO3) between the active layer and the Au electrode.