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

• Published in: Thin solid films 2013-02, Vol.529, p.7-9
• Main Authors: Chen, Yu-Hung, Liu, Jun-Chin, Chen, Yu-Ru, Lin, Je-Wei, Chen, Chun-Heng, Lu, Wen-Haw, Li, Chiung-Nan
• Format: Article
• Language: English
• Subjects: Amorphous silicon-germanium; Annealing; Applied sciences; Barriers; Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electrical conductivity; Electrical properties of specific thin films; Electrical resistivity; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Energy; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; N-type microcrystalline silicon; Natural energy; Photovoltaic cells; Photovoltaic conversion; Physics; Resistivity; Silicon germanides; Solar cell; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2012.06.019

In this work, amorphous silicon-germanium (a-SiGe:H) p-i-n single junction solar cells are fabricated using a 40MHz 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 (600~900nm). 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 0.31eV and 0.20eV , 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. ► Demonstration of thermal annealing in overcoming the s-curve behavior. ► Annealing treatments lead to better n-type microcrystalline silicon thin films. ► Energy conversion efficiency of 6.38% was achieved after post-deposition annealing.