a-SiGeC:H solar cells fabricated near the threshold of the amorphous-to-crystalline transition for narrow gap solar cells and its improvement by modifying interfaces

摘要

a-SiGeC:H thin films have been deposited over a broad range of MMG/SiH4 and H2/SiH4 gas flow ratios. It was observed that the optical band-gap (Eopt) of the films was gradually reduced as either MMG/SiH4 or H2/SiH4 increases. Then, a-SiGeC:H solar cells containing less carbon were fabricated near the threshold of amorphous-to-crystalline transition for the fabrication of narrow-gap solar cells, because high H2 dilution is beneficial for suppressing C incorporation. It was found that, at the fixed MMG/SiH4, the solar cells showed the improving trends in performance under higher H2 dilution, if the a-SiGeC:H thin films did not become crystalline. The optimized conditions were obtained under much higher H2 dilution when MMG flow rates were higher. From the QE measurement under negative bias voltage, it was assumed that the origin of the deterioration of the cell performance was stemmed from the reduced mobility-lifetime (μτ) product due to the presence of C and Ge. The various techniques were employed in order to improve the performance mainly by modifying interface property rather than i-layer itself. As a result, the solar cells were notably improved.