Characterization on the Passivation Stability of HF Aqueous Solution Treated Silicon Surfaces for HIT Solar Cell Application by the Effective Minority Carrier Lifetime Measurement

The traditional passivation processes, standard RCA cleaning and 1% HF aqueous solution immersion, were introduced to passivate the surfaces of p-type Si(100) wafers for heterojunction with intrinsic thin-layer (HIT) solar cell application. The passivation stability was checked by monitoring the time decay of the effective minority carrier lifetime of the Si wafer in air via the microwave photoconductive decay (μPCD) method. The results show that the passivation effect is greatly dependent on the initial surface morphology of the Si wafer. During the subsequent exposure in air, the obtained effective minority carrier lifetime decays rapidly, corresponding to that the Si surface states increase greatly. Such decay occurs more severely on the textured surface than on the polished one, which gives a time limitation to the subsequent processes in the HIT solar cell fabrication. So, such passivation processes need further improvement. The results also prove that the effective minority carrier lifetime measurement can be adopted as an efficient and convenient method to check the passivation stability of the Si surface treated by wet-chemical methods.