Chemical Defects in Organic Solar Cells (ChemDeTOX)

• Applicants: Professor Dr. Carsten Deibel; Professor Dr. Michael Sommer
• Subject Area: Experimental Condensed Matter Physics ; Preparatory and Physical Chemistry of Polymers
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 548903709

Solution-processed organic bulk heterojunction solar cells have been investigated since the 90s, and recently have exceeded more than 18% power conversion efficiency. This progress is impressive in lightof the disordered nature of the thin film containing the two organic semiconductors, donor and acceptor. The occurrence of deep defect states, which was recently reported even for state-of-the-art high-performance organic solar cells, would have a negative impact by increasing the recombination losses and, thus, the dark saturation current – leading to lower photovoltaic performances. The investigation of the chemical or structural origin of such defect states has, however, not received much attention, and a confirmation of this finding is still to be done. Therefore, defect spectroscopy in organic semiconductors deserves an in-depth look, both specifically with respect to chemical defects and in general. This proposal aims at establishing defect spectroscopy in organic semiconductors and semiconductor blends in a comprehensive manner. We focus on the state-of-the-art donor polymer PM6, combined with commercial acceptors, and will synthesise a variety of PM6 analogs with intentionally introduced defects to study their spectroscopic signature and impact on high performance organic photovoltaic devices. Furthermore, we aim to confirm the observation and importance of the midgap states recently reported and, will determine their chemical origin.

• DFG Programme: Research Grants