Study of Transition Region of p-Type SiOx:H as Window Layer in a-Si:H/a-S1-yGey:H Multijunction Solar Cells

We have studied the p-type hydrogenated silicon oxide (SiOx:H) films prepared in the amorphous-to-microcrystalline transition region as a window layer in a-Si:H/a-S1-yGey:H multijunction solar cells. By increasing the H-2-to-SiH, flow ratio (R,) from 10 to 167, the SiOx:H(p) films remained amorphous and exhibited an increased hydrogen content from 10.2% to 12.2%. Compared to the amorphous SiOx:H(p) film prepared at low R-H2, the SiOx:H(p) film deposited at RH, of 167 exhibited a higher bandgap of 2.04 eV and a higher conductivity of 1.15 x 10(-5)S/cm. With the employment of SiOx:H(p) films prepared by increasing RH, from 10 to 167 in a-Si:H single-junction cell, the FF improved from 65% to 70% and the efficiency increased from 7.4% to 8.7%, owing to the enhanced optoelectrical properties of SiOx:H(p) and the improved p/i interface. However, the cell that employed Si0,:14(p) film with RH, over 175 degraded the p/i interface and degraded the cell performance, which were arising from the onset of crystallization in the window layer. Compared to the cell using standard a-SiC,:H(p), the a-Si:H/a-S1-yGey:H tandem cells employing SiOx:H(p) deposited with R-H2, of 167 showed an improved efficiency from 9.3% to 10.3%, with 17, of 1.60 V, J(sc) of 9.3 mA/cm(2), and FF of 68.9%.