Feasibility study on Si-doped ZnO with Cs coating surface for solar cell anode

Using first-principles calculation method, we investigate the possibility of Si-doped ZnO(0001) surface with Cs coating layer applied as the anode material of solar cell based on photon-enhanced thermionic emission (PETE) mechanism. The n-type doping and Cs adsorption process on ZnO(0001) surface are systematically discussed and analyzed. For n-type doping, five Si substitution doping models are established to study the effects of different doping sites on the formation energy, density of state and work function of n-type ZnO (0001) surfaces. Due to the lowest formation energy, the Site-2 doping model with Si replacing the Ga atom at the third bilayer is selected as the Cs adsorption substrate. Moreover, the optimum Cs adsorption site and coverage on Si-doped ZnO (0001) surface are respectively determined. Meanwhile, excessive Cs adsorption will lead to the appearance of "Cs poisoning" phenomenon. The [Cs-ZnO] dipole moment model can be employed to explain the variation mechanism of work function on Cs-covered surfaces. Based on PETE photoemission theory, the conversion efficiency of PETE devices with ZnO as anode material is predicted. These results provide guidelines for the design of PETE anode materials with high-conductivity and low work function.