Emitter optimization for mono- and multicrystalline silicon : a study of emitter saturation currents

Abstract

In this work the influence of varied diffusion parameters for an industrial open tube POCl3 diffusion furnace upon the emitter saturation current density on monocrystalline silicon is investigated. Further on, the effect of phosphorus gettering on multicrystalline silicon and on the sheet resistance on both mono- and multicrystalline silicon is under investigation. In addition, diffusion profiles are determined using the ECV (Electrochemical Capacitance Voltage) technique. Aim of this work is to enhance the performance of lowly doped emitters (80- 140 Ω/sq) applied in a photolithography based high efficiency solar cell process with special respect to defect-rich block cast multicrystalline silicon material. Understanding the influence of temperature, time and gas flow variations during the diffusion process is very important to enhance solar cell performance especially for mc silicon. For such materials the POCl3 gettering effect and the defect kinetics during the diffusion and the cool down phase after the diffusion are of major interest besides the reliable contact formation and low emitter saturation currents resulting in a good blue response of solar cells. The experiments performed in this work demonstrate that different mono- and multicrystalline silicon materials can benefit from adapted diffusion recipes in terms of significantly reduced emitter saturation currents and increased bulk lifetimes resulting in enhanced solar cell efficiencies.