Relating Microstructure Behaviour to Charge Transfer States Properties and Energy Losses in Organic Bulk Heterojunction Solar Cells
Jun Yan a, Elham Rezasoltani a, Mohammed Azzouzi a, Flurin D. Eisner a, Anne A. Y. Guilbert a, Jenny Nelson a
a Department of Physics and Centre for Plastic Electronics, Imperial College London, London, SW7 2AZ, UK.
Oral, Jun Yan, presentation 045
DOI: https://doi.org/10.29363/nanoge.iperop.2020.045
Publication date: 14th October 2019

The microstructure of donor: acceptor blend photoactive layers in organic solar cells directly influences the properties of interfacial charge-transfer (CT) states, and thereby influences the minimum value of the energy loss that can be achieved in the photovoltaic device. However, relatively few studies are able to relate blend phase behaviour directly to device energy losses. In this work, we study the correlation between the phase behaviour of two poly-3-hexylthiophene (P3HT): acceptor blends made using different non-fullerene acceptors, namely IDTBR and IDFBR, and the energy losses of the blend devices. Whilst the two acceptors are chemically very similar, small differences in molecular structure result in large differences in the degree of crystallisation and mixing in the blend films. In particular, P3HT:IDTBR blends shows a higher degree of crystallinity and more phase separated domains, whereas P3HT:IDFBR blends show lower crystallinity and more mixing of polymer and acceptor. The different blends exhibit different trends in terms of energy loss as a function of blend composition, indicating disparate mechanisms on energy losses. To understand this, I will quantify the radiative and nonradiative component of energy losses and apply a model of interfacial charge recombination [1] and models of charge transport in order to relate the measured energy losses to the transport and recombination dynamics in the different blends and finally to the blend microstructure.  I will bring the observations together to discuss the relationship between phase behaviour and recombination losses using the P3HT:acceptor systems as a model.

 

J.Y and J.N. thanks the EPSRC and ERC for financial support.

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