Heat treatment of boron-doped CdS films prepared by chemical bath deposition for solar cell applications

Effects of annealing on the properties of boron-doped CdS films prepared by chemical bath deposition using boric acid as a dopant source were investigated. The crystalline orientation and the grain size of CdS films appeared to be seriously affected by the annealing ambient. The crystal structures of H₂-annealed films were wurtzite type with a preferential orientation of the (002) plane and the grain size slightly increased. For samples annealed in N₂ and air, however, the preferential orientation of the (002) plane disappeared or decreased and the grain size was identical to or smaller than that for H₂ ambient. The dark resistivity decreased by annealing in H₂ and increased further with increasing annealing temperature. For N2 and air ambient, the dark resistivity was larger than that of the H₂-annealed films and the optical transmittance was less than that of the H₂-annealed films. These results suggest that annealing in H₂ ambient is suitable for photovoltaic device application.