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

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 greater than or equal to100 Angstrom has photoconductivity (sigma(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 similar to100 Angstrom, required for window layer, the sigma(ph) of p-a-SiO:H film is similar to 10(2) times higher than that of p-a-SiC:H film. This difference in thickness dependence Of sigma(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 A,window layer. In the former case the Fill Factor of the solar cell is higher by similar to10%. The improvement in Fill Factor is due to the higher sigma(ph) of p-a-SiO:H resulting in lower series resistance.