Magnetic dipolar interaction between correlated triplets created by singlet fission in tetracene crystals

TL;DR

This study investigates the magnetic dipolar interactions between correlated triplets generated by singlet fission in tetracene crystals, providing quantitative insights into the multi-exciton states relevant for organic solar cell efficiency.

Contribution

It offers the first quantitative measurement of magnetic dipolar interactions between triplets in tetracene, advancing understanding of multi-exciton states in singlet fission.

Findings

Magnetic dipolar interaction ~ 0.008 GHz measured

Avoided crossings observed in quantum beats

Results align with theoretical predictions

Abstract

Singlet fission (SF) can potentially break the Shockley-Queisser efficiency limit in single-junction solar cells by splitting one photo-excited singlet exciton (S1) into two triplets (2T1) in organic semiconductors. A dark multi-exciton (ME) state has been proposed as the intermediate connecting S1 to 2T1. However, the exact nature of this ME state, especially how the doubly-excited triplets interact, remains elusive. Here, we report a quantitative study on the magnetic dipolar interaction between SF-induced correlated triplets in tetracene crystals by monitoring quantum beats relevant to the ME sublevels at room temperature. The resonances of ME sublevels approached by tuning an external magnetic field are observed to be avoided, which agrees well with the theoretical predictions considering a magnetic dipolar interaction of ~ 0.008 GHz. Our work paves a way to quantify the magnetic dipolar interaction in organic materials and marks an important step towards understanding the underlying physics of the ME state.