Optimization of hydrogenated amorphous silicon germanium thin films and solar cells deposited by hot wire chemical vapor deposition

Abstract

Optimization of hydrogenated amorphous silicon germanium thin films and solar cells deposited by hot wire chemical vapor deposition, Thin Solid Films (2015), ABSTRACTThis work studies hydrogenated amorphous silicon germanium films, deposited by hot wire chemical vapor deposition, to be used as low band gap absorber material in thin film solar cells. Material properties, such as the bonding configurations, the ambipolar diffusion length and the optical band gap, were examined as a function of the substrate temperature and germanium content. Our best materials were incorporated in single junction solar cells with high long-wavelength response and a tandem solar cell with an efficiency of 10.42%.

S-Shaped Current–Voltage Characteristics in Solar Cells: A Review

“…The need of heterostructures is inherent in these systems to provide efficient charge carrier extraction. Thus, s-shaped I-V curves have been frequently observed in CdTe [6], [58], [59], copper indium (gallium) selenide [CI(G)S] [60]- [62], and a-Si cells [63]- [65].…”

“…Accordingly, solar photovoltaics research has been focusing on the usage of a-Si not as the absorbing material, but rather as passivated contact materials, as described in detail above. However, studies that report s-shaped I-V curves in solar cells with a-Si absorber also found the barriers between absorber and charge transport layers to be the culprit [63]- [65], [85].…”

Very thin and stable thin-film silicon alloy triple junction solar cells by hot wire chemical vapor deposition

“…To achieve this, we have utilized intrinsic layers of hydrogenated amorphous silicon (a-Si:H) and silicon germanium (a-SiGe:H) for the top, middle, and bottom cells, and hot wire chemical vapor deposition (HWCVD) as the fabrication technique. HWCVD allows for the fabrication of high quality low-band gap a-SiGe:H 5,6 and for conformal deposition at high rates. 7,8 HWCVD can contribute to an additional reduction of costs/ Wp compared to plasma enhanced chemical vapor deposition (PECVD), due to lower system and operating expenses as well as its excellent compatibility with roll to roll fabrication.…”

“…Detailed descriptions of the vacuum system and the HWCVD deposition process are given elsewhere. 6,10 Figure 1 shows the refractive indices and the absorption coefficients of three types of absorber materials with different Ge fraction (x ¼ Ge=½Si þ Ge ). The optical constants were obtained from reflection and transmission measurements of individual layers on Corning EAGLE XG V R glass that were fitted using the density-of-states model of O'Leary, Johnson, and Lim.…”

“…As the Ge fraction increases, the optical band gap E g decreases from 1.86 eV for unalloyed a-Si:H (x ¼ 0) to 1.54 eV and 1.37 eV for x ¼ 0.45 and x ¼ 0.63, respectively. 6 The low band gap and high refractive index of the a-SiGe:H materials allow for a thin absorber layer thickness in solar cells, which furthermore preserves the effect of light trapping textures Published by AIP Publishing. 109, 093902-1 APPLIED PHYSICS LETTERS 109, 093902 (2016) throughout the device as compared to the devices with the thicker lc-Si:H layers.…”