Effects of Amorphous Si Substrates on the Optoelectronic Properties of Zinc Phthalocyanine Thin Films

In the current work the effect of amorphous silicon (a-Si) substrates on the structural, optical and electrical properties of zinc phthalocyanine (ZnPc) thin films is explored. ZnPc thin films are coated onto glass and a-Si substrates by the thermal evaporation technique under a vacuum pressure of 10 –5 mbar. It is observed that a-Si substrates lead to a lattice expansion, increased strain, increased stacking faults percentages and increased defect densities. Coating ZnPc films onto a-Si substrates reduced the crystallite sizes from 28 to 24 nm and decreased the energy band gap from 3.20 eV to 2.50 eV. In addition the temperature dependent electrical resistivity measurements has shown that deeper acceptor levels are formed in the energy band gap of ZnPc. Although the room temperature electrical resistivity increased by 45.5% upon coating the films onto a-Si, the light absorption in ZnPc increased by more than 24 times at 2.65 eV. The enhanced light absorption together with the shift in the energy band gap indicates that a-Si makes ZnPc films more adequate for optoelectronic applications.