Effect of sublimation rate and thermal treatments on the photoactivity of chloroaluminum phthalocyanine thin films
Abstract
ClAlPc thin films were grown on SnO2 substrates at various sublimation rates ranging from 100 to 10,000 angstroms min-1. ClAlPc films were also grown at 2000 angstroms min-1 and heat treated at 300 degree(s)C for various periods of time going from 1 to 60 min. All films were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoelectrochemistry in I3-/I- at pH 3. All sublimed ClAlPc films were porous. The sublimation rate only affects the diameter of the rod shaped `crystallites' characterizing the morphology of the material. The short-circuit photocurrent increases with the sublimation rate. It is in direct relation with the total area of the solid-electrolyte interface available for the collection of the photogenerated charges. Selected area diffraction patterns of all as-sublimed films display the characteristic triclinic structure of ClAlPc single crystal. The polycrystalline phase which is responsible for the diffraction pattern is only a minor component of the solid phase. The major part of the film is mostly amorphous. In contact with I3-/I-, there is an uptake of iodine into both amorphous and polycrystalline regions of as-sublimed films. A short (1 min) heat treatment of as-sublimed ClAlPc only alters the structure of the crystalline region of ClAlPc. The new structure is also triclinic but is impermeable to iodine uptake. Longer heat treatments are required to transform part of the amorphous phase of the film into the new triclinic structure. In I3-/I-, the new triclinic structure of ClAlPc is about one order of magnitude less photoactive than as-sublimed ClAlPc.
- Publication:
-
Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XI: Photovoltaics, Photochemistry, Photoelectrochemistry
- Pub Date:
- December 1992
- DOI:
- 10.1117/12.130580
- Bibcode:
- 1992SPIE.1729...13G