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10 September 2019 Effect of triplet exciton diffusion on the open-circuit voltage generation in singlet fission photovoltaics (Conference Presentation)
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The recombination of electron and hole limits the amount of photocurrent that can be generated in a photovoltaic medium. For this reason the physical mechanisms behind free charge generation and recombination in organic photovoltaic diodes form an integral part of scientific research. The most recent studies on OPVs have established the importance of energy absorbance in individual components that form a D-A junction. Free charges can simultaneously be generated across the D-A interface. The fast transport of generated charges away from the D-A interface is required to minimize recombination loss. Free charges can be lost through recombination mainly through two routes- 1) recombination at the interface via CT states, and 2) In situations where excitons are generated far from the D-A interface recombination in the bulk of the organic layer far away from the interface (> LD). Recombination via CT states where an elecotron (hole) in acceptor recombines with a hole (electron) in donor phase is most probable and can be easily resolved via measuring the emission related to corresponding CT energy. However, isolating recombination within the bulk from that occurring at the D-A interface is not trivial, and for this reason it has been largely ignored. In this work, we will present field-dependent photocurrent measurements on the model photovoltaic diodes of tetracene/C60 and rubrene/C60 that unveil recombination hot spots through detailed spectral mapping. We will show that recombination zone starts first in the tetracene layer and shifts to the C60 layer as device thickness increases. Results show that shift in recombination zone has strong implications on effective open-circuit voltage generation in photovoltaic diodes. The spin character of charge recombination behind energy up-converted green electroluminescence observed will be discussed.
Conference Presentation
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Ajay K. Pandey "Effect of triplet exciton diffusion on the open-circuit voltage generation in singlet fission photovoltaics (Conference Presentation)", Proc. SPIE 11094, Organic, Hybrid, and Perovskite Photovoltaics XX, 110940U (10 September 2019);

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