Microstructural, optical and electrical properties of boron subphthalocyanine chloride (B- SubPc- Cl) were investigated in order to use it in energy applications. Field emission scanning microscopy (FE-SEM) was used to investigat the surface morphology and the structural nature of B- SubPc-Cl evaporated thin films. The diffuse reflectance spectra of the as-deposited and annealed B-subPc-Cl thin films were investigated based on Kubelka-Munk (K-M) function. The optical characteristics (specular transmission and reflection) were determined from the analysis the spectrophotometric measurements. Organic/inorganic B- SubPc-Cl / n-Si heterojunction diode was successfully fabricated by means of the conventional thermal evaporation technique of B- SubPc-Cl thin film onto n-Si substrates of (110) preferred orientation. The current density–voltage (J–V) of Au/ B- SubPc-Cl / n-Si/Al heterojunction device was measured at selected temperatures. The essential electrical parameters of the device such as the series resistance, ideality factor, and barrier height were estimated from the analysis of current-voltage characteristics of heterojunction diode ac- cording to the Cheung-Cheung and Norde methods. The Complex dielectric functions such as the real and imaginary dielectric parts, dielectric modulus, and electrical conductivity of Au/ B- SubPc-Cl / n-Si/Al heterojunction device were carried out with the applied frequency in the range 20 Hz to 1 MHz and selected temperatures from 298 K to 473 K. DFT/TD-DFT calculations with B3LYP/6–31 G level of theory were used to study the optimized geometry and some important parameters of B-SubPc-Cl.