Bias and humidity effects on the ammonia sensing of perylene derivative/lutetium bisphthalocyanine MSDI heterojunctions

In this paper, we prepared and studied sensors based on Molecular Semiconductor-Doped Insulator (MSDI) heterojunctions. These original devices are built with two stacked layers of molecular materials and exhibit very specific electrical and sensing properties. We studied the properties of a MSDI composed of the perylenetetracarboxylic dianhydride, PTCDA, or the fluorinated perylenebisimine derivative, C4F7-PTCDI, as n-type molecular material sublayers, and LuPc2 as a p-type semiconductor top layer. Their response to ammonia was compared to that of a resistor formed of only the top layer of the MSDI (LuPc2). Ammonia increases the current in the MSDIs whereas it causes a decrease in the case of LuPc2 resistors, as previously observed for other MSDIs with a n-type sublayer. At first, we showed the significant effect of the applied potential on the response of these sensors. There is an optimum operating point for which the response to ammonia is maximized, which depends on the nature of the samples. The influence of the thickness of the layers was studied, showing a strong influence of this parameter on the sensing properties. MSDIs prepared with fluorinated PTCDI exhibit a higher energy barrier and a lower current. Finally, in general, PTCDA/LuPc2 MSDIs show a strong response to ammonia with a response up to 250% to 30 ppm NH3 at 50% of relative humidity for the MSDI PTCDA/LuPc2 50 nm/50 nm. A discrimination better than 10 ppm between the ammonia concentrations was observed, regardless of relative humidity between 10 and 70% rh. (C) 2015 Elsevier B.V. All rights reserved.