Fabrication and characterization of high efficiency organic solar cell using carbon nanotube/polymer nanocomposites

Abstract

Organic photovoltaic (OPV) devices offer promising advantages such as low-cost and large-area fabrication on flexible substrates. However, the main handicap of these OPV devices is the low power conversion efficiency (PCE). Main limitation of such low PCE is short diffusion length (~10 nm) of exciton (electron-hole pair) in organic materials. Excitons dissociate into free electrons and holes in the donor-accepter interface with this short diffusion length(~10nm) before exciton decay occurs. In recent years, bulk-heterojunction (BHJ) structure was employed to create more dissociation sites by expanding the interface area for exciton dissociation. Still, even if an increased amount of excitons were dissociated into charge carriers, the transport of the dissociated charge carriers toward each electrode would be prevented by low electron and hole mobilities (<$10^{-4} cm^2/V^{-1}s$) in organic materials. Moreover, the narrow absorption range limited visible light of polymer is another reason of low PCE of OPV devices. An alternative approach in this direction is the introduction of one-dimensional (1D) nanostructures like carbon nanotubes (CNTs), which act as exciton dissociating sites and conductive pathway with high carrier mobilities, in addition to being broad absorption range expanded to infrared due to energy band gap(0.8eV) of CNTs. To enhance performance of OPV devices by this approach, well blending of CNTs and photoactive polymers is required. However, relevant work has shown that the performance of OPV devices was compromised because it was difficult to disperse CNTs in polymer matrix homogeneously. In this work, CNT/polymer/fullerene nanocomposites were fabricated from regioregular poly(3-hexylthiophene) (P3HT) and a fullerene derivative 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (PCBM) and functionalized Single Wall Carbon Nanotubes (SWNTs) by alkyl-amide groups for high dispersion of CNT in organic media. Organic solar cell was fabricated from th...