|
Abstract
Organic
semiconductors have been the subject of intense scientific
investigation for the past 50 years. Due to often weak bonding
between organic molecules in the solid state, they share many of the
properties of both semiconductors and insulators. Applications of
these materials include chemical, physical and biological sensors,
electric, electronic, and photonic devices. Low cost production of
these devices is possible by using vacuum evaporation, spin coating,
and drop casting technology. This work describes fabrication and
characterization of organic semiconductor devices such as humidity,
temperature, and light sensors, photoelectrochemical cells,
electrochemical cells, solid-liquid and surface-type rectifying
junctions.
Organic semiconductors have been the subject of intense scientific
investigation for the past 50 years. Due to often weak bonding
between organic molecules in the solid state, they share many of the
properties of both semiconductors and insulators.Applications of
these materials include chemical, physical and biological sensors,
electric, electronic, and photonic devices. Low cost production of
these devices is possible by using vacuum evaporation, spin coating,
and drop casting technology. This work describes fabrication and
characterization of organic semiconductor devices such as humidity,
temperature, and light sensors, photoelectrochemical cells,
electrochemical cells, solid-liquid and surface-type rectifying
junctions.
Organic semiconductors 5,10,15,20-tetrakis(4′-isopropylphenyl)
porphyrin (TIPP), Cu(II) 5,10,15,20-tetrakis(4′-isopropylphenyl)
porphyrin (CuTIPP), Ni(II) 5,10,15,20-tetrakis(4′-isopropylphenyl)
porphyrin (NiTIPP), and Zn(II) 5,10,15,20-tetrakis(4′-isopropylphenyl)
porphyrin (ZnTIPP) are investigated as active materials in
surface-type multifunctional sensors. As electrodes, 100 nm thick Ag
films are deposited on 25 mm × 25 mm glass substrate with 40.0 μm
gap between them. Thin films of TIPP, CuTIPP, NiTIPP, and ZnTIPP of
area 15 mm × 15 mm, are thermally sublimed to cover the gap between
surface-type silver electrodes. A change in electrical resistance
and capacitance of the fabricated devices are observed with the
increase of relative humidity, temperature and illumination.
Hysteresis, response and recovery times are investigated over a wide
range of relative humidity. Activation energies of the porphyrins
are estimated in the solution. Investigation of directivity
characteristics showed that the cell is sensitive in wide range of
angles.
Electrochemical properties of Zn/PVA-I/C, Zn/PVA-KOH/C, Zn/PVA-KOH-I/C,
and Zn/OD/C cells have been investigated. In these cells, polyvinyl
alcohol (PVA)-iodine (I), orange dye (OD) aqueous solutions and
polyvinyl alcohol-potassium hydroxide (KOH), polyvinyl
alcohol-potassium hydroxide-iodine aqueous gels have been used as
electrolytes, while zinc and carbon rods serve as electrodes.The
current-voltage characteristics and open circuit voltage-time,
charge voltage/current-time, and discharge voltage/current-time have
been studied. Effects of concentration of OD in electrolyte have
been examined on the discharge voltage–current, charge
voltage/current–time and discharge voltage/current–time
characteristics. The open-circuit voltages and short-circuit
currents of the cells are observed as dependent on the orange dye
concentration.The efficiency of the current discharge/charge is
found larger at higher concentration of the dye.
Electrochemical properties of Zn/PVA-I/C, Zn/PVA-KOH/C, Zn/PVA-KOH-I/C,
and Zn/OD/C cells have been investigated. In these cells, polyvinyl
alcohol (PVA)-iodine (I), orange dye (OD) aqueous solutions and
polyvinyl alcohol-potassium hydroxide (KOH), polyvinyl
alcohol-potassium hydroxide-iodine aqueous gels have been used as
electrolytes, while zinc and carbon rods serve as electrodes. The
current-voltage characteristics and open circuit voltage-time,
charge voltage/current-time, and discharge voltage/current-time have
been studied. Effects of concentration of OD in electrolyte have
been examined on the discharge voltage–current, charge
voltage/current–time and discharge voltage/current–time
characteristics. The open-circuit voltages and short-circuit
currents of the cells are observed as dependent on the orange dye
concentration. The efficiency of the current discharge/charge is
found larger at higher concentration of the dye.
The solid-liquid junction characteristics of Al/OD aqueous
solution/ITO and Al-CuPc/OD aqueous solution/ITO sandwich type cells
are investigated. In these cells, the aluminum glass slide, copper
phthalocyanine (CuPc) coated aluminum glass slide and indium tin
oxide (ITO) coated glass slide electrodes are employed and as an
electrolyte 0.25 wt.% solution of orange dye in distilled water is
used. Dark current-voltage characteristics of the cells show
rectifying behavior. The parameters, like rectification ratio,
reverse saturation current, ideality factor and junction resistances
are calculated. For interpretation of charge transport mechanism,
dark I-V characteristics are analyzed by modified Shockley equation
and space-charge limited currents approach. |
