Relationship between Device Performance and Grain Boundary Structural Configuration in a Solar Cell Based on Multicrystalline SiGe

The grain boundary character distribution of multicrystalline SiGe (mc-SiGe) solar cells with microscopic compositional distribution was revealed to have a significant effect on the photovoltaic performance of solar cells. This was clarified by comparing the photovoltaic performance of small-area (≈0.02 cm²) solar cells fabricated in a large-area solar cell with their local structures. With increasing fraction of random grain boundaries in a small-area solar cell, the conversion efficiency was found to decrease. On the other hand, Σ3 grain boundaries are found to be dominant in a solar cell with good performance. These results suggest that the development of a crystal growth technique that fully controls the grain boundary character distribution is the key to improving the conversion efficiency of the solar cell based on multicrystalline semiconductors.