Prof. Dr. Jan Behrends: Spins at Work in Energy Conversion and Storage Devices

Unpaired electron spins are unique local probes for elucidating photocurrent generation in organic solar cells as well as redox reactions in polymer batteries. EPR spectroscopy can thus be employed to analyse these processes, identify loss mechanisms, and eventually help developing strategies for improving the performance of devices for energy conversion and energy storage.

The first part of the talk will address the role of electron spins in charging and discharging of organic radical batteries (ORBs). In particular, I will report on the development of a versatile on-substrate electrode setup for spectro-electrochemical EPR measurements on redox conductive polymers for ORBs. Low-temperature ex-situ pulsed EPR measurements on ORB electrode materials indicate the formation of electrochemically inactive islands. I will further report on our recent efforts towards developing cost-effective and accessible electrochemical cells for automated quantitative in-operando EPR experiments as well as electrochemical measurements.

The second part of the presentation will give an overview about how EPR-based techniques in combination with optical excitation can usefully complement all-optical experiments in studying charge separation in materials for solar cells based on organic semiconductors. As one example, I will discuss the EPR properties of intermediate paramagnetic states generated upon fission of one singlet exciton into two separated triplet excitons.