Molecule/quantum dot orbital hybridisation harnesses endothermic singlet exciton fission

Singlet exciton fission (SF) is one of the limited options for exceeding the theoretical limit of solar energy utilisation, the so-called Shockley–Queisser limit. Thus, improving endothermic SF efficiency will significantly contribute to the efficient utilisation of solar energy beyond the existing technology. In this regard, combining SF molecules with quantum dots (QDs) has achieved excellent results. However, the factors underlying the enhanced SF efficiency remain poorly understood. Herein, we discovered that inter-material orbital hybridisation between SF molecules and QDs harnesses endothermic SF. Theoretical calculations and transient absorption measurements of tetracene (Tc)–CdX (X = Te, Se, S) QD composites showed that multiple orbital hybrid levels formed by orbital hybridisation act as intermediate levels to facilitate SF. This result sheds light on alternative factors affecting SF efficiency beyond the molecular packing of SF molecules on the QD surface. The synergy effect on the zero-dimensional molecular assembly on QDs will provide guidance for the development of organic-inorganic hybrid solar cells, which overcome the Shockley–Queisser limit.