Emitter Formation Using a Plasma Immersion Ion Implantation Process for Crystalline Silicon Solar Cells

A plasma immersion ion implantation (PIII) process was studied to form an emitter layer of a crystalline silicon solar cell. At first, optimized conditions of the PIII process were investigated and the best results of a carrier lifetime and implied open-circuit voltage were obtained under the process conditions of a dose of 1.3 x 10(15) atoms/cm(3) and annealing at 875 degrees C. The solar cells with the emitter formed by the optimized PIII process were fabricated and their characteristics were compared with those of the solar cells with the conventional emitters formed by diffusion processes. They showed a higher efficiency compared with the conventional solar cells. Also, in order to analyze the emitter layers, several factors including the doping profile, minority carrier lifetime, saturation current density (J(0)) and internal quantum efficiency (IQE) were investigated. The surface impurity concentration of the emitter formed by the PIII process was about 3 x 10(20) atoms/cm(3) that was much lower than those of the emitters formed by the thermal diffusion processes. Moreover, the dead layer was nearly not found for the PIII process. Because of this decreased surface impurity concentration, J(0) and IQE were improved compared with those of the emitter formed by the thermal diffusion process.