Modelling the PERC structure for industrial quality silicon

The passivated emitter and rear cell (PERC) structure has significant efficiency advantages over the conventional 100% metallised back contact structure for industrial quality multicrystalline silicon. For this material the PERC structure also has only a slightly lower efficiency potential than a more complex structure with rear local diffusions. The PERC structure has previously only been modelled for high efficiency applications. In this work, an optimisation of the PERC structure was performed over a range of wafer resistivities and material qualities. It was shown that the PERC structure has a broad optimum in back contact design, allowing flexibility in manufacturing. There was little difference between a stripe structure and a dot structure of the same contact fraction provided the back contact spacing was optimised in each case. It was shown that contact resistance was negligible in PERC cells compared to spreading resistance for optimised back contact spacings. It was also demonstrated that an analytical expression due to Cox and Strack provided a good approximation for spreading resistance in thick PERC cells, but underestimated the spreading resistance in thinner PERC cells.