Jatindra Rath - Academia.edu (original) (raw)

Papers by Jatindra Rath

Chemical Physics Letters, 2016

$Research paper thumbnail of Scattering, Diffraction, and Geometric Light Trapping in Thin Film Amorphous Silicon Solar Cells on Plastic Substrates$

MRS Proceedings, 2012

ABSTRACTIn this study we compare light trapping in hydrogenated amorphous silicon (a-Si:H) solar ... more ABSTRACTIn this study we compare light trapping in hydrogenated amorphous silicon (a-Si:H) solar cells deposited directly onto polycarbonate (PC) at low temperature…

MRS Proceedings, 2000

ABSTRACTThe Si-H vibration in IR spectra of our device quality poly-Si films grown by hot-wire ch... more ABSTRACTThe Si-H vibration in IR spectra of our device quality poly-Si films grown by hot-wire chemical vapour deposition (HWCVD) made at low wire temperature (Tw=1800 °C) is at 2000 cm−1 whereas in a poly-Si film made at high wire temperature (Tw=1900 °C) both 2000 cm−1 vibrations as well as 2100 cm−1 are observed. On the other hand, the Raman spectra (probing the upper part of the film) of Si-H stretching vibration measured for both these samples show only 2000 cm-1 mode. XTEM micrographs of these films show that whereas the low Tw film has a structure made of closely packed crystalline columns, the high Tw film has conical crystalline structures with amorphous region between them. The crystal cones meet each other towards the top of the film and form a closed structure. This is confirmed by Raman spectrum at 520 cm−1. We attribute the 2100 cm−1 mode to the Si-H bonds at the surface of the cones touching the amorphous regions. The Si-H vibration shifts to 2000 cm-1 when the crysta...

Pizzini/Advanced Silicon Materials for Photovoltaic Applications, 2012

MRS Proceedings, 1999

Two types of poly-Si:H thin films made by Hot Wire CVD have been evaluated with respect to utilis... more Two types of poly-Si:H thin films made by Hot Wire CVD have been evaluated with respect to utilisation in solar cells. Poly-Si:H films made at high hydrogen dilution are highly porous and have large interconnected voids. The void density is 25000/μm-3 as determined by XTEM. On the other hand, poly-Si:H layers made at low hydrogen dilution have a compact structure and a much smaller density of voids. In these films, two types of voids exist: globular voids smaller than 15 nm, and elongated voids, often located between columns of large crystals of 150-250 nm wide at the top. The density for the 5 - 15 nm spherical voids is usually -50/μm3, but larger concentrations often occur locally, up to 1000/pm3, i.e., 0.05% volume fraction. High oxygen content in the poly-Si films made at high hydrogen dilution is largely due to post deposition intrusion of water vapour through the interconnected voids. Profiled layers are made by depositing device quality poly-Si:H layers (low hydrogen dilution...

The applicability of the very high frequency (VHF) plasma-enhanced chemical vapor deposition (PEC... more The applicability of the very high frequency (VHF) plasma-enhanced chemical vapor deposition (PECVD) technique to the fabrication of solar cells in an n-i-p configuration at 100 1C substrate temperature is being investigated. Amorphous and microcrystalline silicon cells are made with the absorber layers grown in conditions close to the amorphous-to-microcrystalline transition, which proved to give the best quality layers. It was observed that post-deposition annealing at 100 1C resulted in a relative increase of the efficiency of up to 50% for both amorphous and microcrystalline cells. For an amorphous solar cell deposited on stainless steel foil with a non-textured back reflector, an efficiency of 5.3% was achieved. A too rough substrate (textured back reflector), with an rms roughness higher than 80 nm, was found to give rise to shunting paths.

Thin-Film Silicon Solar Cells, 2010

Thin Solid Films, 2003

The process parameters for high growth rate poly-silicon films by hot-wire chemical vapour deposi... more The process parameters for high growth rate poly-silicon films by hot-wire chemical vapour deposition have been explored. A four-wire hot wire assembly has been employed for this purpose. High silane to hydrogen flow ratios and high wire temperatures are the key process parameters to achieve high growth rate and growth rates higher than 5 nmys can be achieved. The process conditions to incorporate high hydrogen content into the material for passivation of defects and donor states have been identified as high hydrogen dilution and lower wire temperature. With these procedures poly-Si films deposited at 1.3 nmys showed high ambipolar diffusion length of 132 nm. Incorporating such poly-Si films as i-layer, n-i-p solar cell on stainless steel substrate without back reflector showed an efficiency of 4.4%.

Thin Solid Films, 2006

A new regime of high rate deposition of near-stoichiometric silicon nitride by Hot Wire Chemical ... more A new regime of high rate deposition of near-stoichiometric silicon nitride by Hot Wire Chemical Vapor Deposition was investigated. The layers were tested on multicrystalline silicon solar cells in order to assess their antireflection and passivation properties. The present design of the filament arrangement and the showerhead gas supply system allows for virtually unlimited scale-up and deposition rates of around 3 nm/s were obtained. By varying the SiH 4 flow, the refractive index at 630 nm (n) could be controlled from 1.90 T 0.05 to 2.12 T 0.05, and the extinction coefficient at 400 nm (k) was < 0.007 for all films of interest. The cells had state-of-the-art values for all photovoltaic parameters, similar to cells with a conventional SiN x antireflection coating. An efficiency of 14.3% was reached using HWCVD SiN x for multicrystalline Si solar cells with an industrial emitter.

Thin Solid Films, 2008

Amorphous silicon films have been made by HWCVD at a very low substrate temperature of ≤ 100°C (i... more Amorphous silicon films have been made by HWCVD at a very low substrate temperature of ≤ 100°C (in a dynamic substrate heating mode) without artificial substrate cooling, through a substantial increase of the filament-substrate distance (∼ 80 mm) and using one straight tantalum filament. The material is made at a reasonable deposition rate of 0.11 nm/s. Optimized films made this way have device quality, as confirmed by the photosensitivity of N 10 5. Furthermore, they possess a low structural disorder, manifested by the small Γ/2 value (half width at half maximum) of the transverse optic (TO) Si-Si vibration peak (at 480 cm − 1) in the Raman spectrum of ∼30.4 cm − 1 , which translates into a bond angle variation of only ∼ 6.4°. The evidence gathered from the studies on the structure of the HWCVD grown film by three different techniques, Raman spectroscopy, spectroscopic ellipsometry and transmission electron microscopy, indicate that we have been able to make a photosensitive material with a structural disorder that is smaller than that expected at such a low deposition temperature. Tested in a p-in solar cell on Asahi SnO 2 :F coated glass (without ZnO at the back reflector), this i-layer gave an efficiency of 3.4%. To our knowledge, this is the first report of a HWCVD thin film silicon solar cell made at such a low temperature.

Solid State Communications, 1995

Metastable increase of dark conductivity with light soaking in compensated a-Si : H(B, Li) is rep... more Metastable increase of dark conductivity with light soaking in compensated a-Si : H(B, Li) is reported for the first time. Similarity in the behavior of a-Si : H(B, Li) and a-Si : H(B, P) suggests similar mechanism for light induced Fermi level shift (A&) in both the cases. The kinetics of defect formation, annealing and stretch exponential decay of AE, infer a process involving light induced structural changes. A model has been proposed by which capture of holes at bistable charge trapping sites by deactivation of boron causes metastable increase of conductivity.

Solar Energy Materials and Solar Cells, 2009

We report on the development of fully flexible micromorph tandem solar cells directly on low cost... more We report on the development of fully flexible micromorph tandem solar cells directly on low cost substrates like PET and PEN. The cells are deposited in nip/nip configuration on the plastic substrate coated with a highly reflecting Ag-ZnO back contact. Light trapping is achieved by combining a periodically textured substrate and a diffusing ZnO front contact. Single junction microcrocystalline cell with a stable efficiency of 8.6% and 8.4% are achieved with i-layer thickness of 1.8 and 1.2µm respectively. In tandem devices we obtain an efficiency of 10.9% (initial) with an open circuit voltage of 1.35 V and a FF of 71.5%. These cells are slightly top limited with 11.26 and 11.46 mA/cm2 in the amorphous (270 nm thick) and the microcrystalline sub-cells (1.2 µm thick), respectively. We introduce an intermediate reflector between the bottom and the top cell because it allows increasing the top cell current without compromising stability by a thicker absorber. We present results on ex-situ ZnO and a new material, a low refractive index P-doped siliconoxygen compound deposited in-situ by plasma process, in the same reactor as the micromorph cell.

Solar Energy Materials and Solar Cells, 2006

The hydrogen reaction on a hydrogenated silicon film is in two phases. This is manifested in slow... more The hydrogen reaction on a hydrogenated silicon film is in two phases. This is manifested in slowing down of the hydrogen loss at the growing film. The slow down occurs in phases and both the processes have exponential character. The first phase consists of hydrogen incorporation into the layer and this occurs within the first 50 s. The second phase is of etching. This is confirmed by the similarity between the rate of hydrogen loss in the second phase and the rate of production of silyl species.

physica status solidi c, 2010

Pressure (p) and inter‐electrode distance (d) are important parameters in the process of depositi... more Pressure (p) and inter‐electrode distance (d) are important parameters in the process of depositing hydrogenated nanocrystalline silicon (nc‐Si:H) by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD). High quality nc‐Si:H materials are normally deposited at high pressure (1 mbar < p < 7 mbar). However, systematic research on the combined effects of p and d is rare. In order to optimize nc‐Si:H for solar cells, such effects are investigated for a silane‐hydrogen discharge at high pressure conditions. All nc‐Si:H layers were deposited at fixed hydrogen dilution ratio (H2/SiH4), power and frequency. With optical emission spectroscopy, direct images taken by a photo camera and by 1D SiH4/H2 plasma simulation, three different series were analyzed to study the combined effects of p and d at high pressure. The effects on the crystalline ratio and the porosity of the deposited silicon layers were also investigated. When the p ·d product is constant, the plasma...

Materials Science and Engineering: B, 2013

Quantum dots (QDs) are considered a possible solution to overcome the Shockley-Queisser efficienc... more Quantum dots (QDs) are considered a possible solution to overcome the Shockley-Queisser efficiency limit of 31% for single junction solar cells by efficiently absorbing above band gap energy photons through Multiple Exciton Generation (MEG) or sub band gap energy photons using an Intermediate Band Solar Cell structure (IBSC). For the latter absorption process, we consider tin sulphide (SnS) as a promising candidate, having several advantages compared to the other nanoparticles studied extensively so far, such as CdS, CdSe, PbS, and PbSe; namely it is non-toxic and environmentally benign and thus will be most suitable in consumer products such as solar panels. In this work we propose a new colloidal synthesis method for SnS QDs. We have obtained monodispersive SnS and SnS/In 2 S 3 core-shell nanoparticles with a size of ∼4 nm. Energy dispersive X-ray spectroscopy (EDX) elemental analysis revealed that the particles are indeed SnS and not SnS 2. Furthermore, the conductive nature of the nanoparticles has been inferred by conductivity mapping using a relatively new contactless technique, Torsional Resonance Tunneling AFM (TR-TUNA). These results confirm that the SnS QDs possess all the requirements to be applied as photoactive layers in photovoltaic devices.

Journal of Physics D: Applied Physics, 1997

... Figures 5 and 6 illustrate the absorption characteristics of n-type Si:H films deposited at l... more ... Figures 5 and 6 illustrate the absorption characteristics of n-type Si:H films deposited at low (30 mW cm −2 ) and high (120 mW cm −1 ) powers respectively. ... Symp. Proc. 283 471 [16] Imura T,Kaya H, Terauchi H, Kiyono H, Hiraki A and Ichihara M 1984 Japan. J. Appl. Phys. ...