Monday, 21 February 4:00pm – 5:00pm

This seminar will be delivered in Online – Zoom Please email chemistry.researchsupport@sydney.edu.au for zoom link and password.

Speaker: Mr. Julien Leoni; ARC Centre of Excellence in Exciton Science, School of Chemistry, The University of Sydney

Supervisor: A/Prof. Girish Lakhwani

Title:The multifaceted roles of Perylene Diimides in Organic Solar Cells

Abstract: Owing to their good photophysical properties, perylene diimides (PDI) have been shown to possess great potential in many fields, such as photo-redox catalysis, bio-imaging, and fluorescence detection. Here, we demonstrate the multifaceted roles of PDIs in optoelectronic devices, such as when used in solar cells, optical cavities and even both.

A range of phenyl substituted PDI compounds (bPDI) and commercially available EpPDI were studied as acceptor molecules in bulk-heterojunction organic solar cells using PTQ10 as donor polymer. We report an efficiency of 5.5% in additive-free PTQ10:EpPDI solar cells outcompeting reported monomer PDI based devices in the literature, while bPDI acceptor devices yield ∼2% efficiencies. With the help of light-intensity dependent short-circuit (Jsc) and open-circuit voltage (Voc) measurements in devices and thin film time-resolved absorbance spectroscopy, we show that bPDI acceptor solar cells suffer from geminate and bimolecular recombination losses leading to their poor performance.

While PDIs have been shown to be promising acceptor molecules due to their good electron conductivity, very few reports exist in their use as cathode interfacial layers to promote selective electron transport. Here, we use a range of perylene analogues as cathode interlayers in PTQ10:IDIC solar cells and demonstrate > 0.1V increase in Voc in perylene interlayer devices. With the help of time-resolved absorption and current measurements and numerical drift-diffusion simulations, we show these perylene interlayers promote improved charge extraction, thereby resulting in lower bimolecular recombination and increased Voc.

Lastly, given the narrow bandwidth absorbance and emission spectral features in bPDI molecules, we investigate their utility in achieving strong light matter interactions and its impact on cavity enclosed inverted solar cell architectures. We show that strong light matter coupling is present in perylenes evidenced by existence of half-light, half-matter quasiparticles called polaritons and Rabi splitting > 120 meV. We observe that cavity enclosed inverted solar cells show lower open circuit voltage losses compared to cavity-free counterparts. We hypothesise that this is likely due to change in potential energy surface of perylenes and charge transfer states.

Our results show that PDIs can be used in multi-faceted roles as acceptors, dopants, interfacial layers, and dyes to achieve strong light-matter interactions offering a promising approach to improving device performance of organic solar cells.