Structure and electrical conduction properties of phthalocyanine thin films

Junction properties of nickel phthalocyanine thin film devices utilising indium injecting electrodes

Metallophthalocyanine complexes and related compounds play an important role in many advanced applications and modern technologies mostly by virtue of their characteristic optical absorption and high chemical stability. As a class of materials made well-known by their vivid and fast colors, it is expected that metallophthalocyanines and analogues, e.g. naphthalocyanines, are going to keep their role with the increasing use of natural and artificial light in the technologies of the future. In the present review some relevant properties of phthalocyanines and related macrocycles for technological applications are analyzed. In particular the electrical conductivity and photoconductivity as well as some nonlinear optical properties (mostly optical limiting), of phthalocyanines and related compounds are discussed.

Phthalocyanines as materials for advanced technologies: some examples

Structural control of evaporated lead-phthalocyanine films

Characterization and performance of Schottky diode based on wide band gap semiconductor ZnO using a low-cost and simplified sol–gel spin coating technique

DC electrical measurements have been made for a wide lead phthalocyanine (PbPc) thickness range (d ~ 0.5–5.0 µm). Measurements of capacitance as a function of inverse thickness revealed a low frequency relative permittivity (∊ r ~ 3.9), slightly higher than in copper phthalocyanine. At low voltages Ohm's law was followed, with a thermally-activated hole concentration of (1 · 1–21) × 1016 m-3. Above a threshold voltage Vt, a power-law dependence of current density on applied voltage was observed, indicating space-charge-limited conductivity, Vt varied in the range 0.4–20 V and was approximately proportional to d2, providing further evidence for this effect. The results were accounted for in terms of an exponential distribution of traps of total concentration 2.8 × 1025 m−3 within the bandgap, as observed in similar organic materials.

Transport properties in lead phthalocyanine thin films for use in FET structures

DC current density-voltage measurements have been performed on vacuum evaporated aluminium-lead phthalocyanine-gold sandwich structures for both electrical polarities. The electrical characteristics differed markedly depending on whether the positive hole-injecting electrode was gold (forward-bias) or aluminium (reverse-bias). An extensive study of such characteristics revealed two distinct regions in the forward-bias characteristics. In the first of these a power-law dependence of current density (J) on voltage {V) was observed with exponent n∼4, and this was identified with space-charge-limited conductivity (SCLC) controlled by an exponential distribution of trap levels of approximate concentration 1025 m−3 in agreement with the authors’ earlier work. In the second region a square-law dependence of J on V was observed, which was identified with SCLC controlled by traps of approximate concentration 1026m−3 and situated at a discrete energy level. Under reverse-bias, current density was considerably lower...

Observations of Schottky and Poole-Frenkel emission in lead phthalocyanine thin films using aluminium injecting electrodes

The d.c. electrical properties of aluminium-lead phthalocyanine-gold sandwich structures have been investigated. Samples show space-charge-limited conductivity when the injecting electrode is gold. When the injecting electrode is aluminium they show the Schottky effect at low voltages and Poole-Frenkel emission at higher voltages. The existence of a Schottky barrier is confirmed by capacitance-voltage measurements. © 1992 Taylor & Francis Ltd.

T. S. Shafai

Papers

Transport properties in lead phthalocyanine thin films for use in FET structures

Observations of Schottky and Poole-Frenkel emission in lead phthalocyanine thin films using aluminium injecting electrodes

Electrical characteristics of lead phthalocyanine thin films using aluminium Schottky barriers and gold ohmic contacts