Fabrication, characterization and modeling of a silicon solar cell optimized for concentrated photovoltaic applications

• 22% efficient silicon concentrator solar cells have been realized.
• We describe modeling, design, and fabrication technology.
• Numerical simulations adopting calibrated physical models have been performed.
• Numerical simulations have been exploited for cell design optimization.
• A short-circuit current super-linear effect has been observed and discussed.

Silicon is still an interesting material for developing Concentration Photovoltaic (CPV) cells working at low and medium concentration range. In this work we describe modeling, design, fabrication technology and functional characterization of a small-area silicon solar cell suitable for CPV applications up to 200 suns. Two-dimensional (2-D) numerical simulations by a state-of-the-art Technology Computer Aided Design (TCAD) tool adopting calibrated physical models have been performed for both cell design and deep understanding of its performance. Specifically, the simulations have allowed the development and optimization of front contact grid scheme and design of the cell operating under medium concentration. The cell has been tested by means of a novel indoor concentrator system up to 300 suns and a conversion efficiency higher than 22% has been measured, according to numerical simulations. The dependence of short-circuit current on concentration factor has been observed to be super-linear. An excess of short-circuit current at 300 suns of approximately 8% has been measured. The super-linear effect has been investigated by means of numerical simulations and explained in terms of enhanced carrier diffusion length under concentrated light. The dependence of the super-linear effect on the incoming photon wavelength was also observed and discussed, showing that the super-linearity is due to the spectrum portion above 600 nm only.