Interfacial Composition of the Oxide-Donor Interface: Probing Morphology and Charge Injection/Extraction in Organic Photovoltaics

Abstract

The role of the transparent conducting oxide (TCO) and the organic donor material interface in small molecule planar heterojunction (PHJ) and bulk heterojunction (BHJ) solar cells (OPV) was investigated and are presented as three projects: 1) the influence of the electrode surface composition and energetics on small molecule organic solar cell performance: Polar vs. non-polar donors on indium tin oxide (ITO) contacts, 2) the study of the oxide donor contact electrical properties utilizing metal-insulator-semiconductor capacitor (MIS-C) devices to probe the dark current contributions of a single interface in organic solar cells, 3) the role of the hole transport layer type and morphology in small molecule BHJ solar cells: correlating trap state density with OPV performance and d) using fluorinated subphthalocyanines as multifunctional materials in OPVs. Organic semiconductor material properties are varied and the role of each class of material functions differently when incorporated into an organic photovoltaic. Polar donor materials such as indium (III) phthalocyanine chloride (ClInPc) adopt different molecular configurations on high work function ITO electrodes as opposed to low work function electrodes which sets itself apart from non-polar electron donating materials. We find that not only does molecular orientation effect the optical properties of these thin films, but the charge transfer properties that occur at the oxide/donor interface influence the overall device performance in OPVs and can be probed using MIS-C devices and high resolution photoemission spectroscopy. We also investigate how the morphology of the hole selective interlayer in BHJ OPVs influences the resulting trap state density and OPV performance.