ITO/MoOx/a-Si:H(i) Hole-Selective Contacts for Silicon Heterojunction Solar Cells: Degradation Mechanisms and Cell Integration

Molybdenum oxide is an efficient hole collector for silicon solar cells. However, its optoelectronic properties deteriorate during cell manufacturing. To assess this issue, the optoelectronic properties and microstructure of molybdenum oxide-based hole contacts are evaluated at different steps of the manufacturing process. Molybdenum oxide becomes more absorbing as it reduces when placed in contact with hydrogenated amorphous silicon, triggering the formation of a 2-nm thick SiOx layer, and when annealed after exposure to the plasma used to sputter the transparent conductive oxide. These changes in the contact properties result in a barrier that impedes hole transport when measuring I-V characteristics at room temperature. Nonetheless, cells still reach an efficiency of up to 20.7% when using a front metal electrode screen-printed at 210 degrees C (21.7% for reference cells). Above 60 degrees C, both molybdenum oxide-based and reference cells exhibit the same efficiency as this barrier to hole transport vanishes.