Modeling exciton diffusion in carbon nanotube-based solar cells*

Carbon nanotubes (CNTs) are quasi-one-dimensional materials with a unique set of optical, electronic, and mechanical properties, which have drawn the attention of researchers for energy-harvesting applications. In order to maximize the efficiency of CNT-based solar cell devices, it is crucial to optimize the transport properties of excitons in CNT films. This is a formidable task due to the many factors involved in the exciton transport problem in CNT films.
Here, we use the Monte Carlo technique to simulate exciton diffusion in CNTs. We study how exciton transport depends on various factors. First, we consider various transport regimes: (i) pure hopping and (ii) hybrid intra-tube drift and inter-tube hopping. The former regime describes films where excitons are highly localized due to disorder, while the latter regime is related to high-quality CNT films. Second, we compare the transport properties under various film compositions and morphologies. We use a mechanical simulation engine to create realistic mesh structures, resembling CNT film networks found in experiments. These structures are used to compare the transport properties between CNT composites materials with various degrees of alignment, composition, and density.