Donor-acceptor interfacial structure and photophysics in organic solar cells

The development of new electron acceptor molecules that replace the commonly used fullerene derivatives in solution-processed organic solar cells (OSCs), has led to record-breaking power conversion efficiencies (PCE) over 18%.

These non-fullerene acceptors (NFAs) absorb light from a broader section of the solar spectrum and do not need a high energy level offset at the donor-acceptor interface to generate charges efficiently, which significantly lowers the loss in open-circuit voltage that is typically viewed as OSC technology’s main drawback.NFAs bring along new challenges and the need for new physics to understand the more complex sequence of processes, from dual light absorption paths in donor and acceptor molecules, exciton delocalisation and dissociation, to the free charge carrier transport and collection at the electrodes.

The molecular packing of NFAs at the donor-acceptor interface and the properties of crystalline and amorphous regions throughout the bulk are crucial for efficient splitting of Coulomb bound excitons and trap-free charge transport with minimal losses.We propose a joint experimental-theoretical research project that will advance of fundamental understanding of the structure-property-performance relations at donor-NFA interfaces from the molecular level to the device level.

The ultimate goal of the research is the development of NFA-based organic solar cells with PCEs beyond 20%.