Optical Spectra, Morphology and Photoconductivity of SnPc Thin Films Deposited at Different Temperatures

Thin films of tin (II) phthalocyanine (SnPc) have been thermally evaporated in vacuum on substrates at different temperature (T). Their transmission spectra in the UV, visible and near IR ranges have been measured. It is shown that a 100 nm thick SnPc films becomes almost panchromatic photoabsorbers: the “green gap” characteristic of porphyrinoids can narrow to the range 410–490 nm, and the long-wavelength edge of the Q-band can reach 1100–1200 nm, depending on the growth conditions. At T below room temperature, the films are X-ray-amorphous, and at T > 25°C, the triclinic polymorph accumulates. The structure of the films is always granular, but the size, shape and packing of grains largely depend on T. The specific conductivity of SnPc thin films has been measured in the dark and under continuous white light (solar simulator) or filtered near-infrared light. It is found that for SnPc films grown at elevated Tg, the photo-to-dark current ratio exceeds an order of magnitude under residual illumination at wavelengths longer than 1 µm.