Singlet fission (SF) is a spin-allowed carrier multiplication process in organic systems offering 200% quantum efficiencies, surpassing the Shockley-Queisser limit in conventional photovoltaics. Though the last decade witnessed considerable efforts in understanding the fundamental principles and underlying mechanism of SF, most studies have been based on acene molecules having poor photochemical stability and low extinction coefficients, limiting their applicability. Moreover, suitable materials are limited due to the strict energetic requirements of singlets and triplets. Here, we explore a new class of organic molecules called Pechmann dyes designed based on Baird's aromaticity rule, proposed to undergo singlet fission. We study their photophysics in thin films and present the triplet formation evidenced from ultrafast transient absorption and electron spin resonance spectroscopy. This work elucidates the relationship between structure, aromaticity, and singlet-triplet energetics as a benchmark for designing novel and efficient SF systems for efficient photovoltaics.

Molecular photophysics of singlet fission in thin films: Towards better photovoltaics

ACS Spring 2022

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