Texture etched ZnO:Al coated glass substrates for silicon based thin film solar cells

Hydrogenated microcrystalline silicon ͑ c-Si:H͒ thin-film solar cells were prepared at high rates by very high frequency plasma-enhanced chemical vapor deposition under high working pressure. The influence of deposition parameters on the deposition rate ͑R D ͒ and the solar cell performance were comprehensively studied in this paper, as well as the structural, optical, and electrical properties of the resulting solar cells. Reactor-geometry adjustment was done to achieve a stable and homogeneous discharge under high pressure. Optimum solar cells are always found close to the transition from microcrystalline to amorphous growth, with a crystallinity of about 60%. At constant silane concentration, an increase in the discharge power did hardly increase the deposition rate, but did increase the crystallinity of the solar cells. This results in a shift of the c-Si:H/a-Si:H transition to higher silane concentration, and therefore leads to a higher R D for the optimum cells. On the other hand, an increase in the total flow rate at constant silane concentration did lead to a higher R D , but lower crystallinity. With this shift of the c-Si:H/a-Si:H transition at higher flow rates, the R D for the optimum cells decreased. A remarkable structure development along the growth axis was found in the solar cells deposited at high rates by a "depth profile" method, but this does not cause a deterioration of the solar cell performance apart from a poorer blue-light response. As a result, a c-Si:H single-junction p-i-n solar cell with a high efficiency of 9.8% was deposited at a R D of 1.1 nm/s.

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“…21 Substrate temperatures are ϳ200°C for p-, i-, and n-layer depositions. The c-Si:H p and i layers were deposited with VHF-PECVD at 94.7 MHz.…”

Section: Methodsmentioning

confidence: 99%

Microcrystalline silicon solar cells deposited at high rates

Mai

Klein

Carius

et al. 2005

Journal of Applied Physics

183

123

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“…However, even though high transmission and low resistance are prerequisites, earlier work has shown that surface roughness, feature size, and shape are key parameters for highly efficient light trapping. 27,40 Thus, we concentrate in the following section on ZnO:Al surface structure observed after etching.…”

Section: -3mentioning

confidence: 99%

“…Besides the transparency, it is crucial to develop a TCO with a suitable surface texture which scatters the light very efficiently in order to extend the effective path length within the active silicon layers. 27,28 Thus, a special design of the TCO is necessary to fulfill all these requirements. For initially smooth sputter-deposited ZnO:Al films a surface texture is realized by postdeposition wet-chemical etching.…”

Section: Introductionmentioning

confidence: 99%

The effect of front ZnO:Al surface texture and optical transparency on efficient light trapping in silicon thin-film solar cells

Berginski

Hüpkes

Schulte

et al. 2007

Journal of Applied Physics

488

275

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This study addresses the material properties of magnetron-sputtered aluminum-doped zinc oxide (ZnO:Al) films and their application as front contacts in silicon thin-film solar cells. Optimized films exhibit high conductivity and transparency, as well as a surface topography with adapted light-scattering properties to induce efficient light trapping in silicon thin-film solar cells. We investigated the influence on the ZnO:Al properties of the amount of alumina in the target as well as the substrate temperature during sputter deposition. The alumina content in the target influences the carrier concentration leading to different conductivity and free carrier absorption in the near infrared. Additionally, a distinct influence on the film growth of the ZnO:Al layer was found. The latter affects the surface topography which develops during wet-chemical etching in diluted hydrochloric acid. Depending on alumina content in the target and heater temperature, three different regimes of etching behavior have been identified. Low amounts of target doping and low heater temperatures result in small and irregular features in the postetching surface topography, which does not scatter the light efficiently. At higher substrate temperatures and target doping levels, more regularly distributed craters evolve with mean opening angles between 120° and 135° and lateral sizes of 1–3μm. These layers are very effective in light scattering. In the third regime—at very high substrate temperatures and high doping levels—the postetching surface is rather flat and almost no light scattering is observed. We applied the ZnO:Al films as front contacts in thin-film silicon solar cells to study their light-trapping ability. While high transparency is a prerequisite, light trapping was improved by using front contacts with a surface topography consisting of relatively uniformly dispersed craters. We have identified a low amount of target doping (0.5–1wt%) and relatively high substrate temperatures (about 350–450°C as sputter parameters enabling short-circuit current densities as high as 26.8mA∕cm2 in μc-Si:H pin cells with an i-layer thickness of 1.9μm. Limitations on further improvements of light-trapping ability are discussed in comparison with the theoretical limitations and Monte Carlo simulations presented in the literature.

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“…The generation of a random texture [1][2] or a periodic structure [3][4] in order to disperse the incoming light and increase its optical path inside the cell is the most usual approach. This can be done by texturing the TCO layers [5][6] or the substrate itself [7]. This is usually accompanied by the use of a back reflector layer both in substrate [8] and superstrate [9] structures.…”

Section: Introductionmentioning

confidence: 99%

Spectral analysis of the angular distribution function of back reflectors for thin film silicon solar cells

Escarré¹,

Villar²,

Asensi³

et al. 2006

Journal of Non-Crystalline Solids

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Nowadays, one of the most important challenges to enhance the efficiency of thin film silicon solar cells is to increase the short circuit intensity by means of optical confinement methods, such as textured back-reflector structures. In this work, two possible textured structures to be used as back reflectors for n-i-p solar cells have been optically analysed and compared to a smooth one by using a system which is able to measure the angular distribution function (ADF) of the scattered light in a wide spectral range (350-1000 nm). The accurate analysis of the ADF data corresponding to the reflector structures and to the µc-Si:H films deposited onto them allows the optical losses due to the reflector absorption and its effectiveness in increasing light absorption in the µc-Si:H layer, mainly at long wavelengths, to be quantified.

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Texture etched ZnO:Al coated glass substrates for silicon based thin film solar cells

Cited by 526 publications

References 6 publications

Microcrystalline silicon solar cells deposited at high rates

Microcrystalline silicon solar cells deposited at high rates

The effect of front ZnO:Al surface texture and optical transparency on efficient light trapping in silicon thin-film solar cells

Spectral analysis of the angular distribution function of back reflectors for thin film silicon solar cells

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