Improved organic p-i-n type solar cells with n-doped fluorinated hexaazatrinaphthylene derivatives HATNA-F6 and HATNA-F12 as transparent electron transport material

We study new electron transport materials (ETM) to replace the reference material C-60 in p-i-n type organic solar cells. A comprehensive material characterization is performed on two fluorinated hexaazatrinaphthylene derivatives, HATNA-F-6 and HATNA-F-12, to identify the most promising material for the application in devices. We find that both HATNA derivatives are equally able to substitute C-60 as ETM as they exhibit large optical energy gaps, low surface roughness, and sufficiently high electron mobilities. Furthermore, large electron conductivities of 3.5 X 10 S-5/cm and 2.0 X 10 S-4/cm are achieved by n-doping with 4 wt. % W-2(hpp)(4). HOMO levels of (7.72 +/- 0.05) eV and (7.73 +/- 0.05) eV are measured by ultraviolet photoelectron spectroscopy and subsequently used for estimating LUMO values of (4.2 +/- 0.8) eV and (4.3 +/- 0.8) eV. Both fluorinated HATNA derivatives are successfully applied in p-i-n type solar cells. Compared to identical reference devices comprising the standard material C60, the power conversion efficiency (PCE) can be increased from 2.1 % to 2.4 % by using the new fluorinated HATNA derivatives. (c) 2014 AIP Publishing LLC.