Enhancing performance of amorphous SiGe single junction solar cells by post-deposition thermal annealing

• DOI: 10.1016/j.tsf.2012.06.019
• Publication Date: 2012-06-10T11:31:56Z
• Authors: Yu-Hung Chen; Jun-Chin Liu; Yu-Ru Chen; Je-Wei Lin; Chun-Heng Chen; Wen-Haw Lu; Chiung-Nan Li
• Keywords: Deposition

Abstract In this work, amorphous silicon-germanium (a-SiGe:H) p-i-n single junction solar cells are fabricated using a 40 MHz plasma-enhanced chemical vapor deposition system. Their s-curve characteristics were observed by current density-voltage measurements. Thermal annealing of cells at 150 °C in a vacuum effectively overcame the s-curve behavior. Additionally, comparing the external quantum efficiency spectra of annealed samples with those of as-deposited samples revealed that the spectral response of annealed cells was higher in the long wavelength range (600 ~ 900 nm). Raman spectroscopy and electrical conductivity analyses revealed that the n-type microcrystalline silicon (n-μc-Si:H) layers of as-deposited cells were not optimal. Experimental results indicate that the i/n barrier heights of the as-deposited and annealed samples were 0.31 eV and 0.20 eV , respectively. The high energy barrier implies that the bad collection ability of charge carriers near the i/n interfaces of solar cells. An energy conversion efficiency of 6.38% was achieved after post-deposition annealing. The improvement in efficiency is concluded to have been caused largely by retention of n-μc-Si:H layers of high crystallinity and electrical conductivity after annealing.