Morphology-Dependent Optical Energy Band Gap in Copper- and Manganese- Phthalocyanine Thin Films.*

Metallo-phthalocyanines thin films have been used widely in applications, such as electronic and photonic devices, organic photovoltaic devices, and gas sensors. Copper phthalocyanine (CuPc) and manganese phthalocyanine (MnPc) thin films have been deposited on clean glass substrates by using thermal evaporation at several deposition temperatures to modify the crystal growth. Generally, electrical, and optical properties of CuPc and MnPc thin films depend on the morphology, which includes the grain size distribution (size, shape, and the orientation of stacked molecules), and film surface roughness. The energy band gap is estimated from the optical spectrum of the transmission data and found to vary with deposition temperature. The fundamental energy band gap of MnPc thin films increases for higher deposition temperatures. It has one energy band gap near 3.6 eV, which is in the Q-band region, whereas CuPc thin films have two energy band gaps in both the Soret band region and Q-band region. At low deposition temperatures, CuPc films have gaps at 1.71(2) eV, and 3.05(5) eV. But for higher deposition temperatures, the energy gap decreases to 1.64 eV and 2.93 eV. Consequently, the energy band gap in the Q-band is higher for MnPc than for CuPc.