Influence of n-Doped μc-Si:H Back Surface Field Layer with Micro Growth in Crystalline-Amorphous Silicon Heterojunction Solar Cells

摘要

The back surface field (BSF) plays an important role for the efficiency of the heterojunction intrinsic thin-film (HIT) solar cell. In this paper, the effect of thickness variation in n-type micro crystalline BSF layer was investigated by Raman and spectroscopy ellipsometry. As we increase the crystalline volume fraction (X_c) from 6% to 59%, the open circuit voltage (V_(oc)) increases from 573 to 696 mV with increase in fill factor from 59% to 71%. However, we observed that V_(oc) and FF are decreased over 59% X_c of n-type μc-Si:H BSF layer. It seems that higher X_c micro layer include lots of defects. The quantum efficiency (QE) measurements were demonstrated on optimized thickness of n-doped micro BSF layer. In the long wavelengths region, the QE slightly increases with increasing the n-type μc-Si:H BSF layer thickness from 10 to 40 nm because of BSF effect, whereas the QE decreases when n-type μc-Si:H BSF layer thickness increases from 40 to 120 nm due to defects in the layer. The performance of heterojunction solar cell device was improved with the optimized thickness on n-doped micro BSF layer the best photo voltage parameters of the device were found to be V_(oc) of 696 mV, short-circuit current density of 36.09 mA/cm~2 and efficiency of 18.06% at n-doped micro BSF layer thickness of 40 nm.