Towards an Optimized Emitter for Screen-Printed Solar Cells

The determination of suitable process parameters for POCl3 diffusion, with the aim of minimizing emitter recombination and obtaining satisfactory contactability of the homogeneous emitter, is the aim of this study. It can be shown that different emitters with low R-sheet < 60 Omega/sq can result in significantly different emitter saturation current densities. Regarding the screen-printing metallization procedure, we observe that the resistance of a semiconductor-metal contact can vary on different emitters despite of the same sheet resistance. In this study, the relevant process parameters for emitter optimization using POCl3-diffusion were determined with the help of a design of experiment (DoE). Thus, it is also possible to find optimized diffusion parameters without increasing the sheet resistance of the optimized emitter. To verify the efficiency potential of the emitter, a standard industrial solar cell process is applied, and the outcome is compared with results from simulations using Sentaurus Device. A significant increase in efficiency can be reached, with open circuit voltages > 640 mV and average efficiencies well above 19%.