Alpha-sexthiophene/n− Si heterojunction diodes and solar cells investigated by I–V and C–V measurements

The forward and reverse current density–voltage (J–V) and capacitance–voltage (C–V) characteristics of alpha-sexthiophene (6T)/n−-silicon heterojunction diodes were investigated to clarify the carrier conduction mechanism at the organic/inorganic heterojunction. These observation results indicate that the 6T/n−-Si junction has a current rectification characteristic explained by a Schottky heterojunction model. Diode parameters—the Schottky barrier height and ideality factor—were estimated to be 0.75–0.79 eV and 2.5, respectively. A C–V analysis suggests that the depletion layer is generated solely in the n−-Si layer on a sub-micron scale from the junction at the zero bias and in the reverse bias condition and the diffusion potential was estimated to be 0.4 eV. This heterojunction allows for power generation with power conversion efficiencies up to 0.4% with a simulated solar light exposure of 50 mW/cm2.