Semiconducting single-walled carbon nanotubes (sSWNTs) are excellent candidates as photoabsorbers for next generation solar cells. Currently, the performance of sSWNT-based solar cells, however, has been limited by a lack of an effective strategy to control sSWNT morphology in the active layer. Here we report a two-step fabrication scheme of sSWNT bulk heterojunctions (BHJs) with controllable sSWNT porosity, interconnectivity, and fiber diameter. We first create highly porous interconnected sSWNT aerogels (sSWNT-AEROs), followed by back-filling the pores with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The as-synthesized sSWNT-AERO structure has density as low as 2.5 mg cm-3 and diameter of sSWNT fibers = 10 nm. The sSWNT-AEROs are then filled with PC71BM using spin coating, resulting in sSWNT-AERO-PC71BM nanocomposites with desired thicknesses and well-maintained fiber structure. Photoluminescence measurements show highly effective sSWNT exciton quenching, which is attributed to the large interfacial area between the sSWNT and PC71BM phases and desired sSWNT fiber diameter that matches the inter-sSWNT exciton migration length. We further fabricate sSWNT BHJ solar cells using the sSWNT-AERO-PC71BM structure. The optimized solar cell exhibits a power conversion efficiency of 1.7% and short circuit current density of 7.2 mA/cm2, which are exceptional among polymer-like solar cells in which sSWNTs are designed to replace either the polymer or fullerene component. The photocurrent generation is much more balanced across the solar spectrum than previous reports with 36% peak external quantum efficiency (EQE) in the visible and 19% peak EQE in the near-infrared, where the photocurrent arises from sSWNT. We expect this novel 2-step fabrication scheme to be a versatile and promising approach towards effective sSWNT morphology control and highly efficient sSWNT photoabsorbing solar cells.

Semiconducting carbon nanotube aerogel bulk heterojunction solar cells

248th National Meeting (2014)

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