The Heterojunction Consisting of Crystalline Silicon and Poly (3-methylthiophene)

To understand the junction state between organic and inorganic materials, better measurements were done to determine electrical and photoelectrical properties of a junction consisting of heavily doped n-type silicone and poly (3-methylthiophene) electrochemically prepared on it. Photons absorbed at the junction area induced a photovoltage. Its polarity was in accordance with that anticipated from the electronic levels in the components, but the short-circuited current decreased upon storage in air. The voltage vs. current curve exhibited a clear rectifying characteristic, but breakdown took place when a small reverse voltage was applied. Furthermore, the stability of the junction was never good in air, and the characteristic changed in long storage. These observations suggested that there are at least two states of junction: one intimately interacts through the electron exchange between polymer chain terminals and silicon surface, while the other is only positionally close and allows only the tunneling current. The fomer is rather unstable in air and responsible for the deterioration of the diode.