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. NPG Asia Materials (2016) 8, e278; doi:10.1038/am.2016.72; published online 10 June 2016