Endothermic singlet fission process in harvesting the high-level excitation energy for tetracene-based photodiode

Singlet fission (SF) offers a pathway to surpass the Shockley-Queisser efficiency limit in photovoltaics, with triplet-triplet 1(TT) pair separation being influenced by excitation wavelength. This study investigates SF dynamics using magneto-photoluminescence (MPL) under 403 nm and 440 nm excitation. High-energy excitation (403 nm) yields a higher MPL intensity, indicating a higher degree of SF in the absence of an external magnetic field. These results suggest that excitation energy significantly modulates SF and influences the triplet-triplet 1(TT) pair separation. To confirm this, temperature-dependent MPL measurements reveal the activation energies of 53.36 meV and 68.61 meV, corresponding to the energy required for 1(TT) pair separation for 403 nm and 440 nm excitation, respectively. Incident photon-to current efficiency (IPCE) measurements in tetracene-based devices show a peak at 380 nm, suppressed by fullerene (C60) deposition, confirming the high-energy nature of SF. These findings advance the understanding of 1(TT) pair separation and SF for high-efficiency photovoltaic applications.