Efficiency Uniformization in Crystalline-Si Solar Cells By Numerical Simulation

Efficiency uniformization is to control the efficiencies of mass-produced crystalline-Si solar cells within a narrow range, as efficiency dispersion is a major contributor to the high cost of PV systems. In order to achieve efficiency uniformization, it is necessary to evaluate the effect of material and process variation on cell efficiency, and then determine the key parameters and their allowed ranges. In this work, a simulation tool Synopsys Sentaurus is employed to perform a sensitivity analysis of cell efficiency on material and process variations. The analysis is performed on the most popular commercial cell structure. The typical ranges of material and process variations are used in the analysis. It is found that the diffusion temperature for the front emitter is the most critical parameter for cell efficiency. As the diffusion temperature in a POCl₃ furnace varies from 830˚C to 770˚C, the cell efficiency drops by 5.9% absolute. Substrate resistivity and other process parameters including front metallization and antireflection coating are less important than diffusion temperature. The efficiency variation by these parameters combined is only 0.47% absolute. When the goal of efficiency uniformization is within 1% absolute of the target efficiency, the diffusion temperature is restricted to 815–840˚C. Methods to achieve more uniform emitter diffusion are outlined.