Photoinduced anomalous current changes in some organometallic materials

Photoinduced changes have been investigated by monitoring electrical measurements in some organometallic materials such as ferrocene derivatives, namely, ferrocenecarboxylic acid [Fc(COOH)], acetylferrocene [Fc(COCH3)], ferrocenecarbaldehyde [Fc(CHO)], hydroxymethylferrocene [Fc(CH2OH)]. The investigations were performed in dry nitrogen gas atmosphere at different constant temperatures. Powdery materials were used in sandwich type of cell configuration with constant d.c. bias voltage (27 V) and were exposed to polychromatic light source. Measurements performed in Fc(COCH3) and Fc(CH2OH) with a fixed intensity of exciting light source have shown a drastic change (usual to unusual) in the current vs. time profile. The similar measurement conditions in case of Fc(COOH) and Fc(CHO) showed the unusual/anomalous current vs. time profiles in their entire temperature range of study. Anomalous changes that have been observed in the plot of the photocurrent vs. reciprocal of temperature for each material were completely absent in their corresponding dark current behaviour. The photoinduced changes were almost reversible along with some fluctuations/instabilities in equilibrium current measured after switching off the light source in a particular temperature range. The observed anomalous changes in photocurrent with time and cell temperature have been explained. The effects of various functional groups substituted into ferrocene-unit have been discussed.