Improved photocurrent by using n-doped 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene as optical spacer layer in p-i-n type organic solar cells

Abstract

We introduce 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA-Cl6) as n-dopable electron transport material (ETM) for small molecule organic solar cells. Because of its large optical energy gap of 2.7 eV and its well suited energy level positions, the material can be implemented as a semitransparent spacer layer between the reflecting metal contact and the photoactive C60 acceptor layer in p-i-n type solar cells. By varying the ETM thickness, it is possible to shift the position of the photoactive area with respect to the interference maximum of the optical field distribution. Applying n-HATNA-Cl6 instead of the parasitically absorbing reference ETM n-C60 results in a considerably improved photocurrent density and accordingly in a higher efficiency. At dETM=100 nm the power conversion efficiency is more than doubled as it increases from (100 nm n-C60) = 0.5% to (100 nm n-HATNA-Cl6) = 1.1%.