Exploring the Properties of Organic Semiconductors for Photovoltaic Applications with the NanoWizard® AFM

^{KEYWORDS: Atomic Force Microscopy; AFM; NanoWizard; Conductive AFM; CAFM; Organic Photovoltaic Cells; OPVC; Semiconductors; Polymers}

Energy conversion is one of the hottest topics in today’s research community. In photovoltaics, sunlight is used as a reliable and clean source of energy to generate electricity. Photovoltaic devices have to be simple and have low build cost. In this app note, organic photovoltaics are shown as an alternative to conventional solid-state semiconductors. Organic photovoltaic cells (OPVC) are based on spatial structures (e.g., layers) of conductive or semiconductive polymers, often referred to as organic electronics. In these, the polymer or small organic molecules (dye doped OPVC) are used to accomplish the functions of collecting solar photons, converting the photons to electrical charges and transporting the charges to an external circuit. However, the efficiency of conversion in OPVC devices is currently one order of magnitude lower than solid state-based cells. This is related to the lower charge mobility caused by nanoscale morphonology and energy level mismatch in the hetero-junction in such structures. Here, using AFM with its superior spatial resolution in combination with local electrical measurements (e.g. conductive AFM) under optical excitation is demonstrated as a powerful tool to gain insight into the underlying processes.

This application note shows the analysis of the morphology and electrical properties of a photoconductive polymer as a simple model system for more complex OPVC’s in correlation with exposure of light and defined environmental conditions.

Readers can expect to learn about:

• Conductive AFM (CAFM) experiments under controlled gas environment on semiconductive polymers;
• Application examples showcasing Bruker's NanoWizard AFM and dedicated accessories as a powerful tool for performing conductive AFM current mapping; and
• The seamless integration of the NanoWizard AFM into optical microscopes with fluorescence illumination for investigating the light-dependent behavior of photoconductive, optically active polymers;