Optoelectronic properties of hybrid diodes based on vanadyl-phthalocyanine and zinc oxide. (December 2017)

• Record Type: Journal Article
• Authors: Kiran, M. Raveendra; Ulla, Hidayath; Satyanarayan, M.N.; Umesh, G.
• Is Part Of: Superlattices and microstructures. Volume 112(2017)
• Page Start: 654
• Page End: 664
• Publication Date: 2017-12
• Subjects: Impedance spectroscopy -- Cole-cole plot -- Charge transport -- Hybrid diode -- Phthalocyanine -- Mobility; Superlattices as materials -- Periodicals; Microstructure -- Periodicals; Semiconductors -- Periodicals; Superréseaux -- Périodiques; Microstructure (Physique) -- Périodiques; Semiconducteurs -- Périodiques; 621.38152
• DOI: 10.1016/j.spmi.2017.10.023
• Languages: English
• ISSNs: 0749-6036

Abstract

Abstract: 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 ϕ 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. Highlights: Electron transport properties of ITO/ZnO/Al is studied as a function of annealing temperature. From impedance measurements, the conduction mechanism is observed to be space charge limited with exponential distribution of traps. Mobility is enhanced up to five orders with annealing temperature. Organic-inorganic Hybrid diodes are investigated in ITO/ZnO/VOPc/MoO3 /Al configuration.