Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
3 results
Search Results
Item Investigation of hole-injection in ?-NPD using capacitance and impedance spectroscopy techniques with F4TCNQ as hole-injection layer: Initial studies(Academic Press, 2014) Fernandes, J.M.; Raveendra Kiran, M.R.; Ulla, H.; Satyanarayan, M.N.; Umesh, G.The charge accumulation leading to injection at the organic interface in the sequentially doped hole-only device structure is studied using capacitance and impedance based spectroscopic techniques. In this paper, we investigate the role of p-type dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) in the charge transport properties of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1?-biphenyl)-4,4?-diamine (?-NPD) through sequential deposition. We show that the hole injection into ?-NPD increases with the increase of interlayer (F4TCNQ) thickness by correlating the current density-voltage, capacitance-voltage, capacitance-frequency and impedance measurements. © 2014 Elsevier Ltd. All rights reserved.Item Investigation of hole transport in ?-NPD using impedance spectroscopy with F4TCNQ as hole-injection layer(Academic Press, 2015) Fernandes, J.M.; Raveendra Kiran, M.R.; Ulla, H.; Satyanarayan, M.N.; Umesh, G.The charge carrier transport is studied in N,N?-di(1-naphthyl)-N,N?-diphenyl-(1,1?-biphenyl)-4,4?-diamine (?-NPD) with the incorporation of sequentially doped p-type dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) as hole-injection layer in hole-only device structures. The field dependent mobility of the charge carriers is determined using frequency dependent capacitance, conductance and impedance methods by varying the thickness of ?-NPD. The Poole-Frenkel zero-field mobility and the Poole-Frenkel coefficient thus obtained for each device in all the three methods is found to be almost constant. © 2015 Elsevier Ltd. All rights reserved.Item Optoelectronic properties of hybrid diodes based on vanadyl-phthalocyanine and zinc oxide(Academic Press, 2017) Raveendra Kiran, M.R.; Ulla, H.; Satyanarayan, M.N.; Umesh, G.We report an investigation of the optoelectronic properties of a hybrid p-n diode device fabricated using ZnO film prepared by sol-gel technique on which a VOPc organic film is deposited by vacuum evaporation. The charge transport properties of devices having the configurations ITO/ZnO/Al and ITO/ZnO/VOPc/MoO3/Al were investigated at different annealing temperatures (150 °C, 250 °C, 350 °C and 450 °C) by Impedance Spectroscopy (IS). The structural, morphological, optical and electrical properties were also studied at different annealing temperatures. The parameters related to the ITO/ZnO and ZnO/VOPc interfaces such as ideality factor (n), barrier height (q?B) and rectification ratio (RR) of the diodes were determined from current density-voltage (J-V) characteristics. IS measurements suggest that the large photocurrent generated is due to the decrease in bulk resistance of the device on account of the generation of electron-hole pairs in the organic active layer when exposed to light. The RR and the photocurrent responsivity (Rph) values obtained from the J-V characteristics compare well with those obtained from the IS measurements. It was observed that the absolute value of Rph (470 mA/W) for the p-n diode with ZnO annealed at 350 °C is high compared to that of diodes with different ZnO annealing temperatures. These values also agree well with the values obtained for p-n diodes of other phthalocyanines. Our studies clearly demonstrate that a p-n diode with ZnO film annealed at 350 °C exhibits much better optoelectronic characteristics on account of increased grain size, improved charge injection due to the reduction of barrier height and hence higher (up to 5 orders) charge carrier mobility. © 2017 Elsevier Ltd