Doping Organic Solar Cells for Longer Exciton Diffusion Length
Christian Osborne a, Stoichko Dimitrov a
a School of Physical and Chemical Sciences, Queen Mary University of London
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV23)
London, United Kingdom, 2023 June 12th - 14th
Organizers: Tracey Clarke, James Durrant and Trystan Watson
Poster, Christian Osborne, 271
Publication date: 30th March 2023

The performance of organic solar cells remains significantly lower than inorganic and perovskite devices, largely due to the fundamental difference in how charges are generated within the photoactive layer. Organic semiconductors are excitonic in nature, by which an exciton must diffuse to an interface and separate into free charges. These materials commonly possess diffusion lengths of a few nanometres and thus require a specific device structure to obtain high power conversion efficiencies. In recent years, it has been suggested that trap states introduced from water molecules present in the thin film can impede both exciton diffusion within the photoactive layer and charge transport in devices. In this work, we use a doping strategy with small molecular additives to neutralise trap states and assess the effect this has on diffusion using transient absorption spectroscopy. We found that a greater than two-fold increase to the exciton diffusion length was achieved upon introducing one of the dopant molecules into the thin film of the benchmark semiconducting polymer PM6 and small molecule acceptor 6TIC. This extension is significant, as it can improve exciton dissociation, resulting in higher device photocurrent. Additionally, it could allow for greater flexibility of device structures, increasing viability for large-area printed devices.

Authors would like to thank Queen Mary University of London and UKRI Rutherford Laboratories for financial support.

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