Novel low-cost technique of emitter-junction optimization in silicon solar cells

The emitter-junction dopant-impurity profile has the most significant influence on solar cell efficiency for both laboratory and industrial production purposes. Optimization of the emitter profile, including the junction depth and surface concentration, before solar cell fabrication, therefore, controls the targeted cell efficiency. Several expensive and sophisticated methods are available for determining the dopant-impurity profile of the emitter junction like secondary ion mass spectroscopy (SIMS) and spreading resistance probe (SRP). However, for the first time, we have used a simple method based on anodic oxidation and the Hall Effect to develop and optimize a controlled phosphorous diffusion process for achieving higher cell efficiency in solar cell industry. This method is a cost-effective and highly reliable one for regular diffusion process monitoring in any crystalline silicon solar-cell fabrication process. It can also drastically reduce the process rejection loss due to bad diffusion. Based on the optimized dopant profile, we have fabricated cells with better spectral response in the shorter-wavelength region. Also, the illuminated I-V characteristics were observed at National Renewable Energy Laboratory (NREL) for our standardization purpose.