Inverse Design of Tetracene Polymorphs with Enhanced Singlet Fission Performance by Property-Based Genetic Algorithm Optimization

The efficiency of solar cells may be improved by using
singlet
fission (SF), in which one singlet exciton splits into two triplet
excitons. SF occurs in molecular crystals. A molecule may crystallize
in more than one form, a phenomenon known as polymorphism. Crystal
structure may affect SF performance. In the common form of tetracene,
SF is experimentally known to be slightly endoergic. A second, metastable
polymorph of tetracene has been found to exhibit better SF performance.
Here, we conduct inverse design of the crystal packing of tetracene
using a genetic algorithm (GA) with a fitness function tailored to
simultaneously optimize the SF rate and the lattice energy. The property-based
GA successfully generates more structures predicted to have higher
SF rates and provides insight into packing motifs associated with
improved SF performance. We find a putative polymorph predicted to
have superior SF performance to the two forms of tetracene, whose
structures have been determined experimentally. The putative structure
has a lattice energy within 1.5 kJ/mol of the most stable common form
of tetracene.