Inverted organic solar cells

Metal oxide interlayers shall be investigated to facilitate charge extraction from organic solar cells. Specifically, on the cathode side titania or zinc oxide may be used, while high-work function transition metal oxides (TMOs) (e.g. molybdenium trioxide) can be inserted on the anode side. The increasing interest in these metal oxide interlayers is still facing a substantial lack of understanding of the electronic structure at the particular interfaces of the active donor/acceptor layers and the respective metal oxide. In addition the relation of electronic structure and the resulting consequences for the extraction of charges is not clarified. It is the goal of this interdisciplinary research project to bridge this gap. Specifically, we will focus our study on inverted polymer:fullerene bulk hetero junction (BHJ) solar cells. We will use P3HT:PCBM as a reference system. The results of PES analysis of oxide/organic hetero-interfaces, will be correlated to the I/V characteristics of the corresponding unipolar devices (electron/hole only) and complete solar cells. Very importantly, inverted solar cells comprising titania interlayers commonly show transient I/V characteristics upon illumination with UV light depending on ambient conditions (O2, N2, air, vacuum). To separate interface effects from a simple change of the bulk conductivity upon illumination, we will also consider electrically doped TiO2 layers (e. g. with Nb, Ta, etc.) with a controlled variation of the carrier concentration.
PES analysis of the relevant interfaces is intended to reveal the underlying change of the electronic structure at the interface oxide/organics upon illumination or upon suitable preconditioning. By correlation with I/V data, an understanding of the charge extraction process will be obtained.

Duration:
01.02.2012 - 31.01.2014

Projectleader:
Prof. Dr. T. Riedl