Jatindra Kumar Rath
Other affiliations: Utrecht University
Bio: Jatindra Kumar Rath is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Thin film & Microcrystalline. The author has an hindex of 1, co-authored 2 publication(s) receiving 97 citation(s). Previous affiliations of Jatindra Kumar Rath include Utrecht University.
Abstract: Thin ( 10−2 Ω−1 cm−1) and low activation energy (<0.08 eV) have been achieved for thin films on various oxide substrates i.e., Corning 7059 glass, SnO2 : F, TiO2 and Ta2O5. Deposition of thin p-μc-Si : H is possible on void rich films (a-SiC : H and low-temperature deposited a-Si : H) but not on device quality a-Si : H. Single junction p-i-n cells were made in a superstrate structure using p-μc-Si : H as the window layer directly on top of SnO2 : F coated glass. For the first time an efficiency of 9.63% could be achieved for a single junction cell with a truly microcrystalline silicon p-layer in a superstrate configuration. There is an improvement in the blue spectral response compared to the cell made with a-SiC : H(B) as window layer. However, open circuit voltage and fill factor were critically dependent on the choice of buffer layer at the p/i interface. Computer simulations point out that this can be attributed to the valence band offset between the amorphous i-layer and the microcrystalline p-layer. The buffer acts as a barrier to electron back-diffusion and reduces the recombination in the p-layer. Tandem cells (a-Si : H/a-Si : H) incorporating p-μc-Si : H along with n-μc-Si : H in the tunnel junction showed an efficiency of 9.9% and FF of 0.73. The tunnel junction n-μc-Si : H/p-μc-Si : H needed an oxide interface layer for a good performance. The role of the interface layer may be to increase the tunnel recombination as well as to act as a diffusion barrier to dopants.
Abstract: We report on the synthesis of Si1−x Ge x alloy nanocrystals by very-high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) technique at different silane to germane gas flow ratio (R) in a mixture of (H2 +Ar) dilution gas and H2 dilution gas alone. TEM, SAED, EDS studies and HAADF-STEM mapping of the samples were done to investigate the NCs' size, crystallinity and distribution of Si and Ge in the Si1−x Ge x alloy NCs. The average estimated size of the NCs in all the samples are in the order of exciton Bohr radius of Ge (24.3 nm), thereby indicating the probability of good quantum confinement. The alloy nature of NCs was confirmed in Raman study. The content of Ge in SiGe NCs was evaluated from Raman spectra which show a direct correlation with the fraction of hydrogen flow in the dilution gas mixture.
Abstract: This review article gives a comprehensive compilation of recent developments in low temperature deposited poly Si films, also known as microcrystalline silicon. Important aspects such as the effect of ions and the frequency of the plasma ignition are discussed in relation to a high deposition rate and the desired crystallinity and structure. The development of various ion energy suppression techniques for plasma enhanced chemical vapour deposition and ion-less depositions such as HWCVD and expanding thermal plasma, and their effect on the material and solar cell efficiencies are described. The recent understanding of several important physical properties, such as the type of electronic defects, structural effects on enhanced optical absorption, electronic transport and impurity incorporation are discussed. For optimum solar cell efficiency, structural considerations and predictions using computer modelling are analysed. A correlation between efficiency and the two most important process parameters, i.e., growth rate and process temperature is carried out. Finally, the application of these poly Si cells in multijunction cell structures and the best efficiencies worldwide by various deposition techniques are discussed.
01 Jan 2012
Abstract: Foreword.- Introduction.- Status of heterojunction solar cell R&D.- Basic features of Heterojunctions illustrated by selected experimental methods and results.- Deposition methods of thin film silicon.- Electronic properties of ultrathin a-Si:H layers and the a-Si:H/c-Si interface.- Degradation of (bulk and thin film) a-Si and interface passivation.- Photoluminescence and electroluminescence for a Si:H/c Si device and interface characterization.- Deposition and properties of transparent conductive oxides.- Metallization and formation of contacts.- Electrical and optical characterization of a-Si:H/c Si cells.- Wet-chemical pre-treatment of c Si for a-Si:H/c-Si heterojunctions.- Theory of heterojunctions and the determination of band offsets from electrical measurements.- Modeling and simulation of a Si:H/c Si cells.- Surface passivation using ALD Al2O3.- Introduction to AFORS-HET.- Hands-on experience with simulation tools.- a-Si:H/c-Si heterojunction and other high efficiency solar cells: a comparison.- Rear contact cells.- Progress in systematic industrialization of Hetero-Junction-based Solar Cell technology.
••01 Mar 2011
Abstract: Crystalline semiconductors are very well known, including silicon (the basis of the integrated circuits used in modern electronics), Ge (the material of the first transistor), GaAs and the other III-V compounds (the basis for many light emitters), and CdS (often used as a light sensor). In crystals, the atoms are arranged in near-perfect, regular arrays or lattices. Of course, the lattice must be consistent with the underlying chemical bonding properties of the atoms. For example, a silicon atom forms four covalent bonds to neighboring atoms arranged symmetrically about it. This “tetrahedral” configuration is perfectly maintained in the “diamond” lattice of crystal silicon.
Abstract: The paper describes the way to transfer process technology of state-of-the-art high efficiency thin film silicon solar cells fabrication on cheap plastic (such as PET or PEN) substrates, by two completely different approaches: (i) by transfer process (Helianthos concept) of thin film silicon cells deposited at high substrate temperature, T s (∼200 °C) and (ii) direct deposition on temperature sensitive substrates at low T s (∼100 °C). Adaptation of the process parameters and cell processing to the requirement of the flexible/plastic substrate is the most crucial step. In-situ diagnosis of the plasma has been done to understand the effect of inter-electrode distance, substrate temperature and hydrogen dilution on the gas phase conditions. Whereas, for the transfer process, the inter-electrode distance is a critical deposition condition that needs to be adapted for the flexible substrates, the direct deposition on plastic substrates has an added issue of loss in material quality and the deposition rate due to depositions at low T s . Our studies indicate that ion energy is crucial for obtaining compact films at low temperature and high hydrogen dilution helps to compensate the loss of ion energy at low substrate temperatures. Efficiencies of ∼5.9% and 6.2% have been obtained for n–i–p type a-Si cells on PET and PEN substrates, respectively, using direct deposition. Using an adapted inter-electrode distance, an a-Si/nc-Si tandem cell on plastic (polyester) substrate with an efficiency of 8.1% has been made by Helianthos cell transfer process.