Abstract:

Singlet fission refers to an exciton multiplication process in which a photoexcited singlet exciton splits into a pair of triplet excitons. This process holds the potential to break the efficiency limit of single-junction solar cells. The generation of the intermediate triplet exciton pair is a critical step in singlet fission. In the ground-state configuration, the electronic coupling between the singlet and triplet exciton pair is relatively weak, suggesting that vibronic degrees of freedom may play a significant role. Therefore, unraveling the ultrafast vibronic wavepacket dynamics in singlet fission is essential to understanding the formation mechanism of triplet exciton pairs—and remains key challenges. This review systematically introduces ultrafast spectroscopic techniques used for probing vibronic wavepacket dynamics, provides an in-depth discussion on the vibronic coupling mechanism of intermediate state formation in singlet fission, and summarizes the key scientific issues and technical challenges in this field. 

Key words: singlet fission, wavepacket dynamics, vibronic coupling, coherent vibrational spectroscopy, non-adiabatic transition