Interface Studies of Small-Molecule Organic Photovoltaics; Surface Modifications, Electron Donor Texturing, and Co-Facial Variations at the Donor/Acceptor Heterojunctions

Abstract

The role of the oxide/organic and organic/organic interfaces in small-molecule planar-Heterojunction (PHJ) photovoltaics was investigated with three interrelated projects: i) indium-tin oxide (ITO) bottom contact electrodes were modified with gold nanoparticles (Au-NPs) to improve rates of charge-transfer at the donor/oxide interface, ii) donor layers in OPVs were textured to increase charge generation at the organic/organic' interface, and iii) the effect of co-facial overlap on device performance via tuning of the electron acceptor orientation at the organic/organic interface. The modification of ITO with Au-NPs showed increased performance in small-molecule OPVs when compared to non-processed ITO devices due to the interactions between the Au-NPs and the donor material. Textured TiOPc increased overall device performance by a factor of 2X via the increased surface area, near-IR absorption, and increased mobilities. Modified and un-modified PTCDA acceptors showed that co-facial overlap at the organic/organic' interface is a large determinant in device performance, while the performance in small-molecule planar-heterojunction photovoltaics were severely affected by the pre-treatment process, most likely due to the particular interactions between the oxide and the donor material.