Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells

Armantas Melianas, Fabian Etzold, Tom J. Savenije, Frédéric Laquai, Olle Inganäs, Martijn Kemerink

Research output: Contribution to journalArticleScientificpeer-review

82 Citations (Scopus)
30 Downloads (Pure)

Abstract

In photovoltaic devices, the photo-generated charge carriers are typically assumed to be in thermal equilibrium with the lattice. In conventional materials, this assumption is experimentally justified as carrier thermalization completes before any significant carrier transport has occurred. Here, we demonstrate by unifying time-resolved optical and electrical experiments and Monte Carlo simulations over an exceptionally wide dynamic range that in the case of organic photovoltaic devices, this assumption is invalid. As the photo-generated carriers are transported to the electrodes, a substantial amount of their energy is lost by continuous thermalization in the disorder broadened density of states. Since thermalization occurs downward in energy, carrier motion is boosted by this process, leading to a time-dependent carrier mobility as confirmed by direct experiments. We identify the time and distance scales relevant for carrier extraction and show that the photo-generated carriers are extracted from the operating device before reaching thermal equilibrium.

Original languageEnglish
Article number8778
JournalNature Communications
Volume6
DOIs
Publication statusPublished - 5 Nov 2015

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