In this sense, OV related deep defect states as recombination centers are unfavorable to transfer charge carriers, because of their impact on the mobility of charge carriers. However, a moderate amount of shallow defect states from which electrons can easily be excited to the conduction band at room temperature does not only increase the concentration but also the separation efficiency of photogenerated charge carriers. Taking into account the layered structure of BiOCl, the distance of [Bi2O2] 2+ and adjacent Cl -ion layers is relatively large, which gives rise to weak interaction and high energy barrier for charge carriers migration perpendicular to the sheets. We also can look at this from the point of mobility of charge carriers. According to literature , effective masses of holes along x, y, z direction in BiOCl are 0.95m0, 0.95m0 and 6.31m0, respectively, while effective masses of electrons along x, y, z direction are 0.29m0, 0.29m0 and 1.15m0, respectively. Charge carrier mobility of semiconductors is inversely proportional to their effective mass. Therefore, charge carriers show low mobility in z direction.