Several advantages are available with organic semiconductors, including easy synthesis,
straightforward purification, high solubility, inexpensive manufacture, and significant
industrial significance. Therefore, materials for large-scale electrical and optoelectronic devices
made of organic semiconductors show promise. Therefore, studying the optical properties of
these materials is very important not only for designing the devices, but also for knowing their
absorption limits, determine the type of optical transition and the optical energy gap value to
assess their viability for solar cell fabrication. For instance, we investigated the optical
characteristics of thin films of 4-dimethylaminobenzylidenemalononitrile (DBM). Through the
process of thermal evaporation, the (DBM) thin films were created. Deposition was carried out
on clean optical flat fused quartz substrates for optical measurements at room temperature and
at two different thermal annealing temperatures of 323 and 373 K. Using a double-beam spectrophotometer, the transmittance T(λ) and reflectance R(λ) of DBM thin films with a
thickness of 480 nm were measured in the 200–2500 nm spectral region. It is possible to
determine the absorption index (k) and refractive index (n). Calculations were made for the
optical energy gap and Urbach energy at ambient temperature as well as at various thermal
annealing temperatures (323 and 373K). It was found that the indirect energy gap increases with
increasing thermal annealing from 0.9325 eV for thin film as - deposited to 0.9575 eV at 373.
The optical characteristics of DBM films can be changed by thermal annealing, which has
numerous significant uses, including high-capacity communications networks.. This means
that the material is suitable for use in manufacturing solar cells.