Formation of nanopatterned polymer blends in photovoltaic devices.

In this paper, we demonstrate a double nanoimprinting process that allows the formation of nanostructured polymer heterojunctions of composition and morphology that can be selected independently. We fabricated photovoltaic (PV) devices with extremely high densities (10(14)/mm(2)) of interpenetrating nanoscale columnar features in the active polymer blend layer. The smallest feature sizes are as small as 25 nm on a 50 nm pitch, which results in a spacing of heterojunctions at or below the exciton diffusion length. Photovoltaic devices based on double-imprinted poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (F8TBT)/ poly(3-hexylthiophene) (P3HT) films are among the best polymer-polymer blend devices reported to date with a power conversion efficiency (PCE, eta(e)) of 1.9%.