Disentangling singlet fission dynamics in high quality Rubrene single crystals

Abstract

Singlet fission (SF), which allows one singlet state to be converted to 2 triplets, is one of the most perspective phenomena that may facilitate overcoming of the Shockley-Quiser limit in organic and hybrid photovoltaics. Rubrene, mobility champion of organic electronics, is one of the most popular SF materials. Yet, despite its popularity, SF fundamentals in Rubrene remain strongly debated in the literature due to both experimental and computational limitations. In this work we applied sub-10 fs transient absorption spectroscopy (TAS) to fully disentangle SF mechanism in low-defects high-quality Rubrene single crystals. We found that on 0.2 ps – 6 ns timescale, SF may be treated as 2 components process with half of the singlets to be converted into triplets at 10ps. Fascinatingly, at early times (<0.2 ps) we found additional component to be involved, which may be associated with hybrid state facilitating coherent SF. Based on our experimental findings, we have built a complete model of singlet fission in crystalline rubrene, which may help to resolve current debates on SF in the literature.