Nickel-plated Front Contacts for Front and Rear Emitter Silicon Solar Cells☆

Abstract We investigate the application of nickel-plated front contacts to front and rear emitter silicon solar cells. We compare identically processed p - and n -type Si solar cells featuring (i) a homogeneous phosphorus-diffused n + front, acting as emitter or front surface field and (ii) a full-area aluminum-alloyed p + rear, acting as back surface field or rear emitter. This results in an n + pp + front emitter and an n + np + rear emitter solar cell structure, respectively. We show that the contact annealing temperature for the thermal formation of the nickel silicide (NiSi x ) after the electroless Ni plating has a significant influence on the NiSi x layer thickness. Increasing the temperature from 300 to 450 °C shifts the average thickness to higher values and augments deep NiSi x spikes. The intensified penetration of the n + front by the NiSi x spikes leads to a strong degradation of the front emitter p -type Si solar cell performances due to (i) decreased shunt resistances and (ii) the contamination of the emitter space charge region. We demonstrate that the rear emitter n -type Si solar cells, in contrast, are explicitly more stable. Therefore, by applying n - instead of p -type Si as base material, an improved stability against the thermal Ni contact formation can be easily realized without significant changes in the solar cell fabrication process.