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

Abstract

We study new electron transport materials (ETM) to replace the reference material C60 in p-i-n type organic solar cells. A comprehensive material characterization is performed on two fluorinated hexaazatrinaphthylene derivatives, HATNA-F6 and HATNA-F12, to identify the most promising material for the application in devices. We find that both HATNA derivatives are equally able to substitute C60 as ETM as they exhibit large optical energy gaps, low surface roughness, and sufficiently high electron mobilities. Furthermore, large electron conductivities of 3.5×10−5 S/cm and 2.0×10−4 S/cm are achieved by n-doping with 4 wt. % W2(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.