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

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 (E_opt) 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.