Characterisation of different hole transport materials as used in organic p-i-n solar cells

摘要

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 an; 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 fullerenc C_(60) 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) cm~2/V s, the morphological stability of T_9 = 158℃, and the excellent results of the C_(60):ZnPc bulk heterojunetion solar cell makes the Di-NPB highly suitable for replacement of the MeO-TPD in organic solar cells.