Proceedings Article | 25 April 2008
KEYWORDS: Solar cells, Doping, Absorption, Glasses, Organic photovoltaics, Solar energy, Heterojunctions, Photovoltaics, Electron transport, Visible radiation
To reach higher performances in organic solar cells, each layer has to be optimised with respect to its purpose.
In the case of a p-i-n structured solar cell, the layers are the absorber system, the doped electron and hole
transport layers, and the bottom and top contacts. This work focuses on the investigation and characterisation
of the transparent hole transport materials PV-TPD, PV-TPDoM, Di-NPB, and MeO-Spiro-TPD, as used in
organic p-i-n solar cells. The motivation is to replace the hole transport material MeO-TPD, which has been
used so far despite its morphological instability at elevated temperatures, with an energetically and morphologically
more suitable material. The hole transport materials were investigated for dopability, hole mobility,
absorption, reflection, cyclic voltammetry, and glass transition temperature. Further specific material properties
were determined with simplified structures, e.g. m-i-p diodes, and the standard solar cells, consisting of the
fullerene C60 as acceptor and ZnPc as the donor material. The Di-NPB has turned out to be the best choice
with respect to its intrinsic properties and device parameters. The deep lying HOMO, the high hole mobility
of μ = 1.9 • 10-4 cm2/V s, the morphological stability of Tg = 158°C, and the excellent results of the C60:ZnPc
bulk heterojunction solar cell makes the Di-NPB highly suitable for replacement of the MeO-TPD in organic
