The standard view of singlet exciton fission in organic semiconductor is that one photon creates a singlet exciton which subsequently decays into a correlated triplet pair state (TT) multiexciton states. The triplet pair state then splits to form two free triplets. Although the theoretical description of (TT) is well developed since 1970, it has so far proved difficult to determine the role and nature of the (TT) state in solid films from experiment directly. Here, using a combination of highly sensitive broadband transient absorption and photoluminescence spectroscopies on a range of polyacene films, we demonstrate that the (TT) multiexciton states is bound and energetically stabilised with respect to free triplets in even the most efficient singlet fission materials, such as TIPS-pentacene and pentacene. The (TT) multiexciton state is emissive, and we find that charge-transfer from one (TT) state to the neighboring electron acceptors has a yield of >100%, i.e. more than one charge is transferred per charge-transfer event. Our findings suggest that the formation of spin-correlated (TT) states emits as one particle and generates 2 charges in organic solar cells and thus open a range of fascinating questions regarding the potential to use entanglement to enhance organic photovoltaic efficiency and the application of organic materials in quantum information
Chaw Keong Yong, Andrew J. Musser, Jenny Clark, John E. Anthony, David Beljonne, Richard H. Friend, and Henning Sirringhaus, "Direct observation of entangled multiexciton states in organic semiconductors
(Conference Presentation)," Proc. SPIE 9923, Physical Chemistry of Interfaces and Nanomaterials XV, 992304 (Presented at SPIE Nanoscience + Engineering: August 28, 2016; Published: 10 November 2016); https://doi.org/10.1117/12.2238499.5161498074001.
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