High deposition rate device quality a-Si:H films at low substrate temperature by HWCVD technique

Abstract

Hot wire chemical vapor deposition (HWCVD) provides a low cost fabrication technology for hyrdogenated amorphous silicon (a-Si:H) based thin film single junction and tandem solar cells. In this paper, we report our results on the high deposition rate device quality a-Si:H films deposited by HWCVD at low substrate temperature. Films have been deposited using tantalum filament with highest deposition rates of 16 Å /s and having the desired device quality properties like high photoconductivity gain ( σ ph/ σ dark), low microstructure factor (as revealed by IR spectroscopy), good short range order parameter and acceptable thickness uniformity over the deposited area. An average photoconductivity gain of ≈3×10 5 has been obtained for the films deposited at rates ∼15 Å /s and the substrate temperature of 200 °C. The p- and n-type films have also been deposited by the HWCVD. Single junction p–i–n solar cells on ASAHi U-type substrates, fabricated using these layers have an efficiency of 5.1% under AM1.5 illumination. Depositing anti-reflection coating on front side, reflection coating before back contact and using textured TCO layer for light trapping would further improve the efficiency of the cell.