The Pulsed PECVD technique involves modulating the standard 13.56 MHz RF plasma, in the kHz range. This allows an increase in the electron density during the ‘ON’ cycle, while in the ‘OFF’ cycle neutralizing the ions responsible for dust formation in the plasma. In this work, we report the increase of i-layer growth rate and silane gas utilization rate (GUR) for amorphous Si p-i-n solar cells grown in a large area (30 cm × 40 cm) single chamber deposition system. The i-layer growth rate of 5.4 Å/sec with a GUR of >15% has been achieved, which shows a device efficiency of 8.3% (almost same as of our conventional PECVD grown a-Si:H solar cell with ilayer growth rate of ∼1 Å/sec). We also deposited microcrystalline Si p-i-n devices using the Pulsed PECVD technique. The crystallite orientation of the films changes from a random to a (220) orientation near the microcrystalline-to-amorphous transition. The effects of crystallite orientation, grain boundaries and ion bombardment during growth on the solar cell performances are investigated. An efficiency of 4.8% for single junction μc-Si:H p-i-n device has been achieved for the i-layer thickness of 0.9 μm.

The role of p/i interface in nanocrystalline Si p-i-n type solar cells is very critical due to the fact that the nc-Si grown by CVD technique often starts with an amorphous incubation phase, the extent of which sensitively varies with the film growth conditions. We used the reflectance spectra at UV region, where the additional reflections (at 365 nm and 275 nm) appear due to the presence of any crystalline phase, to get an idea about the structure of the film at p/i interface. In this work, the usual pulsed PECVD technique has been modified to provide for extra degrees of freedom to manipulate the growth surface reactions and hence the control of initial film growth via altering the density and energy of various radicals (like H, SiH/sub 3/ etc.) and ions. The use of modified pulsed PECVD method for a surface treatment on nc-p layer leads to an elimination or a reduction of the incubation layer at the p/i interface and thereby improves the device performances significantly.

Pulsed plasma enhanced chemical vapour deposition (PECVD) involves modulation of standard 13.56 MHz RF plasma in the kilohertz range. This allows an increase in the electron density during the 'ON' cycle, while in the 'OFF' cycle, neutralising the ions responsible for dust formation in the plasma. The authors report the development of state-of-the-art nanocrystalline Si (nc-Si:H) materials using a pulsed PECVD technique with 220 crystallite orientation, grain size of ∼200 Å, low O concentration and a minority carrier diffusion length Ld of ∼1.2 μm. The crucial effects of the p/i interface and the incubation layer have been investigated and an efficiency of ∼7.5% for a single junction nc-Si:H p-i-n device has been achieved for an i-layer thickness of 1.4 μm, using non-optimised textured substrates

The pulsed PECVD technique allows an increase in the electron density during the 'ON' cycle, while in the 'OFF' cycle it neutralizes the ions responsible for dust formation in the plasma. We have developed a modified pulsed PECVD technique, which has the inherent ability to reduce powder formation in the plasma and to grow nc-Si:H p-i-n solar cells. An efficiency of /spl sim/7.5% (FF of 0.69) at an i-layer thickness of /spl sim/1.4 /spl mu/m has been obtained by optimizing the i-layer growth temperature. The 7.5% efficiency device is (220) oriented with I/sub 220//I/sub 111/ value of /spl sim/2.0 and exhibits no significant Si-O bonding in FTIR, which yields a hydrogen content of /spl sim/7 at%.

We report on the use of pulsed plasma-enhanced chemical vapor deposition (P-PECVD) technique and show that “state-of-the-art” amorphous silicon (a-Si:H) materials and solar cells can be produced at a deposition rate of up to 15 Å/s using a modulation frequency in the range 1–100 kHz. The approach has also been developed to deposit materials and devices onto large area, 30 cm×40 cm, substrates with thickness uniformity (<5%), and gas utilization rate (>25%). We have developed a new “hot wire” chemical vapor deposition (HWCVD) method and report that our new filament material, graphite, has so far shown no appreciable degradation even after deposition of 500 μm of amorphous silicon. We report that this technique can produce “state-of-the-art” a-Si:H and that a solar cell of p/i/n configuration exhibited an initial efficiency approaching 9%. The use of microcrystalline silicon (μc-Si) materials to produce low-cost stable solar cells is gaining considerable attention. We show that both of these techniques can produce thin film μc-Si, dependent on process conditions, with 1 1 1 and/or 2 2 0 orientations and with a grain size of approx. 500 A. Inclusion of these types of materials into a solar cell configuration will be discussed.

The use of a graphite filament in the “hot wire” chemical vapor deposition technique is demonstrated to produce “state-of-the-art” intrinsic and doped (p- and n-) amorphous silicon (a-Si:H) material and microcrystalline silicon (μc-Si) materials. Preliminary p-i-n type solar cells have led to a conversion efficiency of >8.5%. The filament is found to be rugged and remains intact even after deposition of ∼500 μm in thickness. This is in contrast to the use of conventional filament materials, such as W or Ta, whose longevity is limited to less than a few microns of deposition. Unlike the case of a Ta filament, the deposition rate remains constant with the use of a graphite filament.

For the ''Hot Wire" chemical vapor deposition (HWCVD) method to be applicable for photovoltaic applications certain critical technical issues need to be addressed and resolved such as, lifetime of the filaments used reproducibility, large area demonstration of the material and stable devices. We have developed a new approach which addresses some of these problems, specifically longevity of the filaments and reproducibility of the materials produced. This new technique does not seem to introduce contaminants into the materials from the source and can produce high quality amorphous Silicon (intrinsic and doped) and intrinsic microcrystalline silicon films.

The pulsed plasma deposition can increase the deposition rate of amorphous silicon (a-Si) without an increase in the particulate count in the plasma which is an important factor determining the yield of commercial products such as active matrix displays. In this paper, we report the deposition of a-Si at rates of up to 15Å/sec, using a modulation frequency in the range of 1–100kHz and the impact it has on solar cell conversion efficiency. The hot wire CVD deposition technique has attracted a considerable amount of interest because of the ability to produce a-Si at a high deposition rate and with low hydrogen concentration which could minimize the instability phenomena. Further, under suitable conditions, low temperature polycrystalline silicon can be produced. We present data of high deposition rates for a-Si (>15A/s) and polycrystalline Si and discuss their usefulness to photovoltaic applications.

For the “Hot Wire” chemical vapor deposition technique (HWCVD) method to be applicable for photovoltaic applications, certain critical technical issues need to be addressed and resolved such as: lifetime of the filaments, reproducibility, large area demonstration of the material and stable devices. We have developed a new approach (patent applied for) which addresses some of these problems, specifically longevity of the filaments and reproducibility of the materials produced. The new filament material used has so far shown no appreciable degradation even after deposition of >200 μm of amorphous silicon (a-Si). We report that this can produce “state-ofthe-art” a-Si with a dark conductivity of <10 −10 (Ohm*cm) −1 and photoconductivity of >10 −5 (Ohm*cm) −1 this material can also be doped p- or n-type. We also provide data using XRD as well as the Raman spectra. These materials have been incorporated into simple Schottky barrier structures. The development of microcrystalline silicon materials is also discussed.

The pulsed plasma technique has been shown to increase the deposition rate without an increase in the particulate count in the plasma which is an important factor determining the yield of commercial products such as active matrix displays. In this paper, we report the deposition of amorphous silicon at deposition rates of up to 15 Å/sec, using a modulation frequency in the range of 1-100kHz. These materials have been incorporated into a simple p/i/n solar cell and thin film transistor (TFT) configurations. We report on the effect of the conversion efficiency as a function of the modulation frequency, which in turn is related to the deposition rate. We also report on the TFT performance with modulation frequency and compare the results with devices made under the conventional continuous wave PECVD plasma at 13.56MHz.

For the "Hot Wire" chemical vapor deposition technique (HWCVD) method to be a viable approach for photovoltaic applications, certain critical technical issues need to be addressed and resolved such as filament lifetime, reproducibility, and the ability to scale the technique to large area substrates. We have developed a new approach (patent applied for) that addresses some of these problems, specifically longevity of the filaments and reproducibility of the materials produced. The new filament material used has so far shown no appreciable degradation even after deposition of 500 pm of amorphous silicon (a-Si). We report that this technique can produce "state-of-the-art" a-Si and that a solar cell of p/i/n configuration exhibited an initial efficiency approaching 9%. The development of microcrystalline silicon materials and devices is also discussed, and we report on large area materials development (30 cm X 30 cm) using this technique.