Deep blue energy harvest photovoltaic switching by heptazole-based organic Schottky diode circuits

We report novel photovoltaic (PV) switching based on the low exciton-binding energy property of an organic heptazole (C26H16N2) thin film after fabrication of an heptazole-based Schottky diode. The Schottky diode cell displayed an instantaneous voltage of 0.3 V as an open circuit voltage (VOC) owing to the work function difference between the Schottky and ohmic electrode under deep blue illumination. Four tandem diode cells therefore produced ∼ 1.2 V. As a PV diode circuit can be formed using an even number of diodes, a photo-excited charge accumulation takes place, generating VOC in the central electrode of the tandem diode array by illuminating one half of the array. An electron-hole recombination then also takes place in that electrode by illuminating the other half, making the VOC decrease to 0 V. Utilizing this charge accumulation and recombination under deep blue illumination, we successfully demonstrated quite fast PV optical switching, logic gating and, ultimately, the gate switching of an organic field-effect transistor. We therefore concluded that our self-powered PV-induced switching was novel and promising enough to open a new door for energy harvest-related device applications in organics.