Improved FF in P-Si heterojunction solar cells due to optimized ITO/emitter contact

In this paper, we focused on the effect of deposition parameters of a-Si:H (n) emitter layer and its influence on fill factor (FF) of p-type silicon hetero-junction solar cell. a-Si:H (n) films deposited by PECVD at different temperatures and DC plasma current were characterized and incorporated into SHJ solar cells. The optical and structural characterization results have shown that temperature has significantly more effect on a-Si:H properties than the other deposition parameters such as doping gas flow and deposition power. JV measurements have shown that n-a-Si:H emitters deposited at 250°C lead to significantly higher FF due to reduced contact resistance between a-Si:H (n) emitter layer and ITO on the front side of SHJ. Test structures fabricated to evaluate the ITO/a-Si(n) contact indicate that n-layers deposited at 200°C or below have non-ohmic blocking contacts with ITO while those deposited at 250°C have low resistance ohmic contacts. This suggests that the commonly observed `S-curves´ can be partially due to the ITO/a-Si heterocontact. The n-layers deposited at 250 °C on double side polished p c-Si resulted in an FF of 76.3% with an open-circuit voltage (V_oc) of 603 mV, a short-circuit current (J_sc) of 30.7 mA/cm² with efficiency 14.1% without an a-Si:H layer for the surface passivation.