Investigating Hydrogen Behavior at a-Si:H/c-Si Interfaces through Electrical Measurement and Chemical Analysis

Amorphous and crystalline silicon interface (a-Si:H/c-Si) plays a crucial role for achieving record-high efficiency silicon heterojunction (SHJ) solar cell for its exceptional electrical passivation quality. Despite its importance, the degradation mechanisms at interfaces remain poorly understood and often associated with hydrogen loss at the interfaces. Determining H kinetics at the interface, however, is challenging due to the conductivity of the a-Si:H. Here, we introduce a capacitance-voltage (C-V) measurement technique operating at cryogenic temperature (77K), minimizing leakage current in a-Si:H diodes to guarantee trap occupancy under bias. Additionally, we developed a light-bias-temperature stress system to further facilitate the ion migration through the breakage of metastable Si-H bonds, which can be used to determine hydrgoen ions by monitoring flatband potential shift (V_FB). Preliminary results suggested that under 1-sun illumination and reverse biasing at 80^oC can drive the positively charged ion moving from a-Si:H(i)/c-Si interface toward metal contact in a-Si:H(p)/a-Si:H(i)/c-Si(n) structures. We hypothesize these ions to be positively charged hydrogen, although, further spectrometric analysis, correlated with optical emission spectroscopy, is needed to gain deeper insight into the role of hydrogen for better understand the metastability of the a-Si:H/c-Si interface under illumination.