Multicrystalline Silicon Thin Film Research Articles

Multi crystalline silicon thin films grown directly on low cost soda-lime glass substrates

Liquid phase crystallization of silicon is a promising technology platform to grow multi crystalline silicon thin films on foreign substrates. For solar cell application it has already been demonstrated that open circuit voltages of up to 661 mV [1] and efficiencies of up to 15.9% [2] can be achieved on a silicon layer of a few microns only. However, while the quality of the material has been continuously improved, the cost factor of the utilized substrate has been given little attention. The present work focuses on the technology transfer from technical glass substrates to low cost soda-lime glass substrates to become more attractive for commercial applications. We demonstrate that despite a large difference in the expansion coefficient between soda lime glass and silicon absorber layer, adhesive silicon thin films can be produced under certain conditions. On these first layers, we were able to fabricate solar cells, which in their cell and material properties were only ~30% below the values of their technical glass counterparts.

Optimized emitter contacting on multicrystalline silicon thin film solar cells

We present an optimized contacting scheme for multicrystalline silicon thin film solar cells on glass based on epitaxially crystallized emitters with a thin Al2O3 layer and a silver back reflector. In a first step a 6.5 µm thick amorphous silicon absorber layer is crystallized by a diode laser. In a second step a thin silicon emitter layer is epitaxially crystallized by an excimer laser. The emitter is covered by an Al2O3 layer with a thickness ranging from 1.0 nm to 2.5 nm, which passivates the surface and acts as a tunnel barrier. On top of the Al2O3 layer a 90–100 nm thick silver back reflector is deposited. The Al2O3 layer was found to have an optimal thickness of 1.5 nm resulting in solar cells with back reflector that achieve a maximum open‐circuit voltage of 567 mV, a short‐circuit current density of 27.9 mA/cm2, and an efficiency of 10.9%. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Multicrystalline silicon thin film solar cells on glass with epitaxially grown emitter prepared by a two-step laser crystallization process

In this paper, we demonstrate a two-step laser crystallization process for thin film silicon solar cells on glass. In a first step a 5 µm thick amorphous silicon layer is crystallized by a diode laser to get the absorber. The multicrystalline layer consists of grains with sizes in the range of 1 mm to 10 mm. In a second step a thin amorphous silicon layer is epitaxially crystallized by an excimer laser to form the emitter.Epitaxy was investigated in a fluence range of 700 to 1200 mJ/cm2. The resulting thickness of the emitter is measured and numerically simulated, both resulting in 185 nm for a fluence of 1100 mJ/cm2. The solar cells achieve maximum open circuit voltages of 548 mV, short-circuit current densities of up to 22.0 mA/cm2 and an efficiency of 8.0%.

Nanowire Arrays in Multicrystalline Silicon Thin Films on Glass: A Promising Material for Research and Applications in Nanotechnology

Silicon nanowires (SiNW) were formed on large grained, electron-beam crystallized silicon (Si) thin films of only ∼6 μm thickness on glass using nanosphere lithography (NSL) in combination with reactive ion etching (RIE). Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) studies revealed outstanding structural properties of this nanomaterial. It could be shown that SiNWs with entirely predetermined shapes including lengths, diameters and spacings and straight side walls form independently of their crystalline orientation and arrange in ordered arrays on glass. Furthermore, for the first time grain boundaries could be observed in individual, straightly etched SiNWs. After heat treatment an electronic grade surface quality of the SiNWs could be shown by X-ray photoelectron spectroscopy (XPS). Integrating sphere measurements show that SiNW patterning of the multicrystalline Si (mc-Si) starting thin film on glass substantially increases absorption and reduces reflection, as being desired for an application in thin film photovoltaics (PV). The multicrystalline SiNWs directly mark a starting point for research not only in PV but also in other areas like nanoelectronics, surface functionalization, and nanomechanics.

Sputtered amorphous silicon thin films for diode laser crystallization

Multicrystalline silicon thin films with large grains (100 μm) on glass are useful for thin film solar cells and for thin film transistors. These films can be prepared by diode laser irradiation of amorphous silicon films, which previously had been deposited by PECVD or electron beam evaporation. In this paper, the applicability of sputtered amorphous silicon thin films on glass for diode laser crystallization is investigated. For this process the sputter gas content in the films and their optical properties, particularly the absorption for the diode laser wavelength of 808 nm, are crucial. The sputtering parameters gas pressure and power are optimized for increasing the optical absorption and for decreasing the sputter gas incorporation. It is demonstrated that if using optimum deposition parameters diode laser crystallization leads to large grained multicrystalline silicon thin films. The crystallized layers show, different to previous results, a preferred (100)-orientation.

Silicon nanowire-based solar cells

The fabrication of silicon nanowire-based solar cells on silicon wafers and on multicrystallinesilicon thin films on glass is described. The nanowires show a strong broadbandoptical absorption, which makes them an interesting candidate to serve as anabsorber in solar cells. The operation of a solar cell is demonstrated with n-dopednanowires grown on a p-doped silicon wafer. From a partially illuminated area of0.6 cm2 open-circuit voltages in the range of 230–280 mV and a short-circuit current density of2 mA cm−2 were obtained.

Design and Cost Evaluation of A Large-Scale Manufacturing Process of Multicrystalline Silicon Thin Films for Solar Cells Using Copper-Silicon Solution.

大粒径を持つ薄膜多結晶シリコン（Si）を低コストに製造する方法として銅（Cu）－Si溶液を用いた溶解析出法に着目し，その製造プロセスの設計および評価を行った．低コスト化のためには，低コスト基板上でのSiの成長が必要である．この成長を基板上でシリカをアルミニウムで還元して核形成させる新しい手法で可能にできることを実験により確認した．また製膜モデルと実験により推定された拡散係数の値を用い，高速製造プロセスの設計ができた．それは，アルミナを基板とし，溶液を乗せた基板を25°C/mの温度勾配中を20mm/sで移動させ，1,000°Cから800°Cまで冷却を行う問に過飽和となったSiを徐々に析出させる量産プロセスである．太陽電池を年産1GWPで製造するケースについて，投入原材料，電力消費量，設備費，建屋代，人件費からコストの推定を行った結果，薄膜製造コストは¥ 6.3/WPとなり，現状のキャスト法による多結晶Si基板に比べて大幅な低コスト化が可能であることが示された．

Study of hot wire chemical vapor deposition technique for silicon thin film

Micro and multi-crystalline silicon thin films have been prepared in the growing rate of more than 10 Å/S by hot wire (HW) CVD. The crystallite size of the films ranges from 0.1 to 1 μm. The effects of processing parameters on the property of the films have been systematically studied. The energy gap ranges from 1.5 to 1.12 eV when substrate temperature changes from 250°C to 450°C. The conductivity of the doped films is as high as 10 (Ω cm) −1. An anomalous behavior of hot palladium wire in an atmosphere of silane at low pressure is reported and preliminarily explained. The reason why tungsten wire is easy to break during silicon thin film deposition by hot wire CVD is discussed.