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Energetics and Kinetics Requirements for Organic Solar Cells to Break the 20% Power Conversion Efficiency Barrier

Oskar Sandberg Orcid Logo, Ardalan Armin

The Journal of Physical Chemistry C, Volume: 125, Issue: 28, Pages: 15590 - 15598

Swansea University Authors: Oskar Sandberg Orcid Logo, Ardalan Armin

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DOI (Published version): 10.1021/acs.jpcc.1c03656

Abstract

The thermodynamic limit for the efficiency of solar cells is predominantly defined by the energy band gap of the used semiconductor. In the case of organic solar cells, both energetics and kinetics of three different species play a role: excitons, charge transfer (CT) states, and charge-separated st...

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Published in: The Journal of Physical Chemistry C
ISSN: 1932-7447 1932-7455
Published: American Chemical Society (ACS) 2021
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa57309
Abstract: The thermodynamic limit for the efficiency of solar cells is predominantly defined by the energy band gap of the used semiconductor. In the case of organic solar cells, both energetics and kinetics of three different species play a role: excitons, charge transfer (CT) states, and charge-separated states. In this work, we clarify the effect of the relative energetics and kinetics of these species. Making use of detailed balance, we develop an analytical framework describing how the intricate interplay between the different species influences the photocurrent generation, recombination, and open-circuit voltage in organic solar cells. We clarify the essential requirements for equilibrium among excitons, CT states, and charge carriers to occur. Furthermore, we find that the photovoltaic parameters are determined not only by the relative energetics between the different states but also by the kinetic rate constants, highlighting the importance of slow exciton recombination at low energetic offsets. Finally, depending on the kinetic parameters, we find an optimal power conversion efficiency exceeding 20% at energetic offsets around 0.1 eV. These findings provide vital insights into the operation of state-of-art non-fullerene organic solar cells with low offsets.
Keywords: Carrier Dynamics, Electrical Connectivity, Equilibrium, Excitons, Recombination
College: Faculty of Science and Engineering
Funders: This work was funded by the Welsh Government’s Sêr Cymru II Program through the European Regional Development Fund and Welsh European Funding Office. A.A. is a Rising Star Fellow also funded by the Welsh Government’s Sêr Cymru II Program through the European Regional Development Fund, Welsh European Funding Office, and Swansea University Strategic Initiative in Sustainable Advanced Materials. This work was also funded by UKRI through the EPSRC Program Grant EP/T028511/1 Application Targeted Integrated Photovoltaics. The authors thank Dieter Neher and Koen Vandewal for fruitful discussions.
Issue: 28
Start Page: 15590
End Page: 15598

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