Development of high quality P-type hydrogenated amorphous silicon oxide film and its use in improving the performance of single junction amorphous silicon solar cells

Abstract

By using radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) method (13.56 MHz) we have developed high quality wide band gap p-type hydrogenated amorphous silicon oxide (p-a-SiO:H) films having characteristics suitable for use as the window layer for single and multijunction amorphous silicon (a-Si) solar cells. The films have been characterized in detail. The p-a-SiO:H films having thickness ≥100 Å has photoconductivity (σ_ph) one order of magnitude higher than that for p-type hydrogenated amorphous silicon carbide (p-a-SiC:H) films having similar band gap. However, at thickness ≥100 Å, required for window layer, the σ_ph of p-a-SiO:H film is ~10² times higher than that of p-a-SiC:H film. This difference in thickness dependence of σ_ph has been attributed to the structural difference of the two types of window layers. We have fabricated single junction p-i-n structure a-Si solar cells on transparent conducting oxide (TCO) coated glass substrates with both p-a-SiO:H and p-a-SiC:H film as the window layer. In the former case the Fill Factor of the solar cell is higher by ~10%. The improvement in Fill Factor is due to the higher σ_ph of p-a-SiO:H resulting in lower series resistance.