Carrier drift velocity balance mechanism in Si-based thin film solar cells using graded microcrystalline SiGe absorption layer

摘要

The basic idea of balancing the carrier drift velocity in the absorption layer was proposed to improve the conversion efficiency of Si-based thin film solar cells. Using the graded microcrystalline i-SiGe absorption layer to modulate the energy band, the driven electric field of holes was increased from 5.92 kV/cm to 7.26 kV/cm, while the driven electric field of electrons was kept at 5.92 kV/cm. Compared with the step i-SiGe absorption layer, the drift velocity ratio of electrons and holes was more balanced. The improvement mechanism of the p-Si/graded-i-SiGe-Si solar cells was further analyzed using the measurement of the biased quantum efficiency. Consequently, the short-circuit current density and the associated conversion efficiency of the p-Si/graded-i-SiGe-Si solar cells were improved from 21.40 +/- 0.47 mA/cm(2) to 26.36 +/- 0.56 mA/cm(2) and from 7.43 +/- 0.23% to 9.15 +/- 0.25%, respectively compared with the p-Si/step-i-SiGe-Si solar cells. (C) 2015 Elsevier Ltd. All rights reserved.