Polysilicon Passivating Contacts in Mass Production: The Pursuit of Higher Efficiencies

The application of polysilicon passivating contacts in silicon solar cells has significantly increased the solar cell efficiencies in mass production and the technology is experiencing rapid growth in coming years. Commonly applied in the form of n-type doped polysilicon (poly-Si) passivating contacts on the rear surface to minimize parasitic absorption, the effective suppression of metal silicon interface recombination on the rear surface has in turn highlighted the limitations of the front surface boron diffusions. In this work, the optimization of the front surface boron diffusions and selective emitters, enhancement of the screen printing technology, and reduction of the poly-Si layer thickness have been integrated into large area commercial n-type silicon solar cells to reduce the front surface recombination, shading losses and parasitic absorption. The optimization culminated in improved short circuit current density of 42.24 mA/cm2, open circuit voltage of 719.1 mV and fill factor of 83.66%, and an overall independently certified solar cell efficiency of 25.41%. We present an updated model and loss analysis for the champion solar cell, which shows that front surface recombination remains as one of the primary losses. The updated model was utilized to identify the dependence of cell efficiency on surface recombination, contact resistivity and sheet resistance, and the criteria for further optimization of the front surface.