Study of electronic transport properties of some new N-(p-R-phenacyl)-1,7-phenanthrolinium bromides in thin films

The electrical conductivity (σ) and thermoelectric power (S) of six newly synthesized high resistivity organic salts, N-(p-R-phenacyl)-1,7-phenanthrolinium bromides (T compounds), were investigated as a function of temperature.Thin-film samples (d = 0.11–2.22 μm) deposited from ethanol solutions (an immersion technique) onto glass substrates were used.It was established that samples with stable structure and reproducible electronic transport properties can be obtained if, after their deposition, respective films are submitted to a heat treatment within temperature range 297–513 K.The surface morphology of organic samples was examined by AFM technique, corroborated to optical microscopy.The studied organic salts behave as typical n-type polycrystalline semiconductors. The thermal activation energy of electrical conduction laid in the range 0.78–0.92 eV, while the ratio of charge carrier mobilities ranged between 1.09 and 1.24.The correlations between semiconducting parameters (activation energy of electrical conduction, ratio of carrier mobilities, etc.) and molecular structure of the compounds have been discussed.In the higher temperature range (390–513 K), the model based on band gap representation is suitable for the explanation of electronic transfer in investigated compounds, while in the lower temperature range, the Mott's variable-range hopping conduction model was found to be appropriate.The present compounds are also promising for thermistor applications.

► N-(p-R-phenacyl)-1,7-phenanthrolinium bromides thin films are n-type semiconductors.
► Their extended conjugation and packing capacity favor d.c. electrical conductivity.
► The band model representation is suitable in the higher temperature range (T > Tc).
► The Mott's variable-range hopping model operates in the lower temperature range.
► The actual organic salts hold promise for thermistor applications.