Highly efficient organic solar cells using doped carbon nanotubes

Abstract

Organic photovoltaic (OPV) cell is a good candidate for cost effective, solution processable and light weight electronic devices. Typically fabricated OPVs are consisted of ITO (anode), active layer coated from P3HT(poly(3-hexylthiophene)) / PCBM([6,6]-phenyl-C61-butyric acid methyl ester) blend solution and metal cathode layer. However, excitons generated from conjugated polymers have a few nanometers diffusion length, such that charged carriers cannot be completely dissociated into each electrode including ITO and metal cathode. To solve this problem, we introduced n-type and p-type doped one-dimensional nanostructured carbon nanotubes (CNTs) within P3HT / PCBM blend solutions. n-type and p-type CNTs mean nitrogen and boron replaced carbon atoms in the graphite networks respectively. n-type and p-type CNTs can split excitons generated from conjugated polymers and easily transfer the charged carriers. Therefore, CNTs provide a good charge pathway to improve the carrier mobility within active layers of OPVs. We also found that n-type and p-type substitutional atoms in the CNTs can modify the HOMO, LUMO, and work function. Therefore, we can design the structure of OPVs by modifying the work function. Doped CNTs in active layer increased the carrier transfer rate, which enhanced the short-circuit current density and power conversion efficiency under AM1.5G illumination ($100mWcm^{-2}$).