In this special work, two types of material, which are undoped and Mn doped TiO2 thin films, have been produced by spin coating technique, and then their structural, morphological and optical properties have been measured at different Mn doping rates. Four different doping ratios, undoped, 1, 3 and 5% Mn doped TiO2 have been both experimentally and theoretically investigated and some significant enhancements have been reported. The results of X-ray diffraction (XRD) such as dislocation density, strain, and crystallite size have indicated that undoped, 1, 3 and 5% Mn doped TiO2 thin films had the phase of anatase at 450 °C. It has been observed that the peak intensity of 3% Mn doped TiO2 films has decreased compared to undoped and 1% Mn doped TiO2 while the peak intensity has increased for 5% Mn doped TiO2. The refractive indices and dielectric coefficients of the undoped and Mn doped TiO2 thin films have also been calculated. The undoped and Mn doped TiO2/p-Si heterojunction diodes has exhibited photosensitive behaviour in the illuminated environment. 1% Mn doped TiO2/p-Si heterojunction diode indicated the highest photocurrent. The electrical parameters of all diodes have been calculated and compared to the conventional J-V and Norde methods. Additionally, 1% Mn doped TiO2/p-Si heterojunction diode has been modelled by using the SCAPS-1D program, and J ph values have also been calculated based on the shallow donor density (N D ). The experimental and theoretical J ph values of this diode were found to be compatible with each other.