Amino functionalized carbon nanotubes as hole transport layer for high performance polymer solar cells

In this work, we demonstrated the synthesis of amino functionalized MWNTs (af-MWNTs) via a simple and facile hydrothermal process and the af-MWNTs was acted as the hole transport layers (HTLs) of polymer solar cells (PSCs) based on active layers of Poly[N‑9″‑hepta‑decanyl‑2,7‑carbazolealt‑5,5‑(4′,7′‑di‑2‑thienyl‑2′,1′,3′‑benzothiadiazole)] (PCDTBT) and fullerene derivative [6,6]‑phenyl‑C71‑butyric acid methylester (PC71BM). Comparing with the control devices, devices based on af-MWNTs HLTs achieved an optimal power conversion efficiency (PCE) of 6.970%, leading to 17.6% enhancement comparing to the control device. The af-MWNTs HTLs exhibited remarkable enhancement on electrical conductivity, which was beneficial to the hole extraction and transport on interface. The enhancement of PCE was mainly attributed to the superior hole transport and extraction capabilities. Meanwhile, the af-MWNTs exhibited a suitable work function (WF) which was beneficial to hole extraction from the photoactive layer to the ITO anode. The experimental results indicated that the af-MWNTs HTLs not only presented excellent optical and electrical properties, but also played an important role for improving the efficiency of PSCs.