Chemically-treated single-walled carbon nanotubes as digitated penetrating electrodes in organic solar cells

Abstract

In this work, we fabricated and characterized organic photovoltaic (OPV) devices with hybrid composite anodes containing single-walled carbon nanotube (SWCNT) networks sandwiched between ITO and PEDOT : PSS. The SWCNTs used were initially grown on silicon wafers by a surfactant-free process based on ACCVD (alcohol catalytic chemical vapor deposition), and then transferred to glass substrates with pre-patterned indium-tin-oxide (ITO) electrodes for the fabrication of our OPV devices. We also integrated H₂SO₄/HNO₃-treated and N₂H₄-treated SWCNT networks into OPV devices to investigate the effect of chemically-treated SWCNTs on OPV devices' performance. We found that open-circuit voltage (V_oc) of our OPV devices was insensitive to SWCNTs' work function shifting caused by the employed chemical treatments, while their short-circuit current (J_sc) and power conversion efficiency (PCE) both varied in the order of: reference devices < devices with pristine SWCNT networks < devices with H₂SO₄/HNO₃-treated SWCNT networks < devices with N₂H₄-treated SWCNT networks. In particular, we found that integration of N₂H₄-treated SWCNTs into the hybrid composite anode could enhance J_sc by 12% to 20% in P3HT : PCBM OPV devices (with PCE up to 4.02%). The improved performance in devices integrated with N₂H₄-treated SWCNTs can be attributed to (i) better crystallinity of the P3HT polymer, and (ii) increased hole-transport efficiency of the hybrid composite anode, both induced by the penetration/digitation of SWCNTs into the P3HT polymer layer.