Deposition conditions, hydrogen content, and the Staebler-Wronski effect in amorphous silicon

The Staebler-Wronski effect (SWE) is examined as a function of hydrogen content (C_H) and the local H bond structure. The SWE is examined through the rate of degradation of solar cells due to light exposure (at room temperature) and the steady-state defect density that can be established through high-temperature (T >150°C) degradation. Structure and C_H are carefully controlled by the photo-CVD (chemical vapor deposition) reactor conditions. Growth conditions for altering C_H with a minimum of other changes are identified. Films with a total C_H of 7 and 11% were grown at the same substrate temperature and characterized. The initial density of defects in both materials was low (~2E15/cm²-eV) but the stability was drastically reduced in the high-C_H films and devices. The change in stability due to increased C_H is consistent with the SW precursor being a hydrogen-rich region