Endothermic Singlet Fission Process in Harvesting the High-Level Excitation Energy for Tetracene-Based Photodiode

Singlet fission (SF) provides a viable mechanism to surpass the Shockley-Queisser efficiency limit in photovoltaic devices, where excitation energy plays a pivotal role in modulating the SF process. In this study, the SF dynamics are systematically characterized by measuring magneto-photoluminescence (MPL) under two distinct excitation wavelengths (403 and 440 nm) in a tetracene-based thin film. 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 and 68.61 meV, corresponding to the energy required for ¹(TT) pair separation for 403 and 440 nm excitation, respectively. Moreover, the incident photon-to-current efficiency (IPCE) measurements of the tetracene-based photodiode exhibit a relatively high response in the 300–400 nm wavelength range, peaking at 380 nm. Notably, the integrated current density (J) within this spectral region contributes ≈31% to the total photocurrent. These results indicate the possibility of harvesting high-level excitation energy through SF in a tetracene-based photodiode and suggest the importance of ¹(TT) pair separation in optimizing the SF-based photovoltaics.