All-Small-Molecule Organic Solar Cells – Performance, Electronic & Microstructure Properties
Pascal Kaienburg a, Moritz Riede a
a Clarendon Laboratory, Department of Physics, University of Oxford, UK, University of Oxford, Parks Rd, Oxford, United Kingdom
nanoGe Fall Meeting
Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)
#BRIGHT - Recent Breakthroughs in Organic Photovoltaics
Barcelona, Spain, 2022 October 24th - 28th
Organizers: Thomas Anthopoulos and Safa Shoaee
Invited Speaker, Pascal Kaienburg, presentation 360
Publication date: 11th July 2022

Organic solar cells (OSCs) based exclusively on small molecules have distinct advantages over polymer-based OSCs for commercial applications. Unlike polymers, small molecules have a defined molecular weight and can be purified easily, resulting in a simpler, more reproducible synthesis with controlled quality. Solution-processed All-small-molecule (ASM) OSCs have reached 17% power conversion efficiency, and ASM-OSCs fabricated via vacuum thermal evaporation (VTE) are leading OSC commercialization. However, ASM-OSCs remain less investigated than polymer-based OSCs in terms of their semiconducting and microstructure properties.

Here, we perform extensive optoelectronic characterization on high-performing ASM-OSC deposited from solution and in vacuum to quantify absorption, voltage losses and charge transport – probed via ellipsometry, sensitive EQE and CELIV, respectively. Example systems include VTE DCV5T-Me:C60, and solution-processed BTR-Cl:Y6. We find that certain VTE ASM-OSC achieve strong absorption, decent charge carrier mobility, or voltage losses matching corresponding polymer-based OSCs but no VTE blend combines all these favourable properties. We further investigate the blend microstructure in terms of phase separation. Interdiffusion experiments offer a thermodynamic perspective while the actual phase separation in probed via soft X-rays. This talk gives an overview over prospects and challenges of All-Small-Molecule organic solar cells and provides an outlook on open research questions.

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