Build-up of Triplet State Population in Operating TQ1:PC71BM Devices Does Not Limit Their Performance
byS. Karuthedath, J. Gorenflot, A. Melianas, Z. Kan, M. Kemerink, F. Laquai
Year:2020
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Build-up of Triplet State Population in Operating TQ1:PC71BM Devices Does Not Limit Their Performance
S. Karuthedath, J. Gorenflot, A. Melianas, Z. Kan, M. Kemerink, F. Laquai. J. Phys. Chem. Lett. 2020, DOI: 10.1021/acs.jpclett.0c0075
Abstract
Triplet generation in organic solar cells has been considered a major
loss mechanism. Determining the density of the triplet state population
in an operating device is challenging. Here, we employ transient
absorption (TA) spectroscopy on the quinoxaline–thiophene co-polymer TQ1
blended with PC71BM, quantify the transient charge and
triplet state densities, and parametrize their generation and
recombination dynamics. The charge recombination parameters reproduce
the experimentally-measured current-voltage characteristics in charge
carrier drift-diffusion simulations, and they yield the steady-state
charge densities. We demonstrate that triplets are formed by both
geminate and non-geminate recombination of charge carriers and decay
primarily by triplet-triplet annihilation. Using the charge densities in
the rate equations describing triplet state dynamics, we find that
triplet state densities in devices are in the range of charge carrier
densities. Despite this substantial triplet state build-up, TQ1:PC71BM
devices exhibit only moderate geminate recombination and significantly
reduced non-geminate charge recombination, with reduction factors
between 10-4 to 10-3 compared to Langevin recombination
Keywords
TQ1:PC71BMOrganic Solar CellsTriplet state dynamics