Identifying mobile ions kinetics at a-Si:H/c-Si interfaces by cryogenic C-V measurement after bias-temperature stress |
Guang-Yu Lee1, Jorge Ochoa Bueno2, Mariana Bertoni2, David Fenning1 1Department of Nanoengineering, University of California, San Diego, CA, United States /2School of Electrical and Energy Engineering, Arizona State University, Tempe, AZ, United States |
The interface between amorphous and crystalline silicon (a-Si:H/c-Si) plays a crucial role in high-efficiency silicon heterojunction (SHJ) solar cells due to its exceptional electronic passivation quality. Despite its significance, there is only a limited understanding of the mechanism of degradation over time that has been observed in SHJ cells, where it is often taken to be due to hydrogen loss at the a-Si:H/c-Si interface. However, determining H transport kinetics is challenging, making it difficult to establish a concrete understanding of long-term stability. Here, we use a cryogenic capacitance-voltage (C-V) measurement approach to suppress electronic conductivity across the a-Si:H/c-Si interface. Incorporating periodic cryo-C-V measurements into a light-bias-temperature stress sequence permits the determination of mobile ion motion by monitoring flatband potential shifts (ΔVFB). The preliminary results on model a-Si:H/c-Si test structures indicate mobile ion motion under 1-sun illumination at 80°C when a 1V bias falls across the contact. This result can be interpreted as a positively charged ion moving away from a-Si:H(i)/c-Si interface in a a-Si:H(p)/a-Si:H(i)/c-Si(n) device. Further chemically-species measurements are required for discriminating which mobile ion is responsible, but a tentative assignment can be made to positively charged hydrogen. Overall, the cryogenic C-V measurement approach can identify mobile species in passivated contacts using bias-temperature-stress protocols without being affected by the conductivity of selective contacts nature. |