Sourav Mandal

Development of n-type microcrystalline SiOx:H films and its application by innovative way to improve the performance of single junction µc-Si:H solar cell

Light trapping is one of the fundamental necessities of thin film based solar cell for its performance elevation. Back reflection of unused light of first pass is the key way to improve the light trapping phenomena. In this study we have reported the development of n-type hydrogenated microcrystalline silicon oxide (n-µc-SiO:H) layers of different characteristics. The deposition has been done by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. The detailed characterization of the films include the following: (1) electrical properties (2) optical properties like E04 (3) structural studies which include crystalline fraction by Raman spectroscopy and grain size by X-ray diffraction measurement, FTIR spectroscopy, AFM and TEM studies. n-µc-SiO:H layer has been introduced as the n-layer of single junction p–i–n structure µc-Si solar cells. By various techniques the optimum use of n-µc-SiO:H layer for enhancing the performance of µc-Si:H solar cells has been done. It has been found that by using suitable bilayer of two different n-µc-SiO:H layers, it is possible to increase the solar cell performances. The maximum efficiency obtained without any back reflector is 8.44% that is about 8.9% higher than that obtained by using n-µc-Si:H layer as n-layer in the solar cells.

A Three-Pass Algorithm for Generation of BE-Matrices from IUPAC Names

One of the basic needs of chemoinformatics is to represents chemical compounds graphically in computer. Among several matrix representations of chemical graphs, BE-Matrix is one of the popular choices to represent molecules. There are several line notations available to input a chemical graph. Although several algorithms exist to convert from different line notations to suitable computer representations but using IUPAC Name, a line notation, to give input to the computer is not a popular method, because of the lack of suitable algorithm from IUPAC names to BE-Matrix or its variants. However, each and every chemist is familiar with IUPAC names, and therefore it calls for development of a suitable algorithm for such purpose. In this paper a three-pass algorithm for generating BE-Matrix from IUPAC name have been proposed and illustrated with suitable examples. The third pass of the algorithm can independently be used to convert from symbolic chemical names of any compound to BE-Matrix, thus making task of a chemist much simpler.

Band Offset Reduction at Defect-Rich p/i Interface Through a Wide Bandgap a-SiO:H Buffer Layer

In single junction p-i-n solar cells, the optical losses can be mitigated by inserting the wide band gap amorphous silicon oxide layer at the defect-rich p/i interface. In this paper, a simulation and experimental study on the performance of p-i-n solar cells by inserting the intrinsic hydrogenated amorphous silicon oxide (i-a-SiO:H) buffer layer at the p/i interface is reported. The i-a-SiO:H film has been deposited by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) (13.6 MHz) at a low substrate temperature of approximately 230°C. The p/i interface is crucial to solar cell performance because the first few nanometers of the intrinsic layer are a defect-rich layer, having the band gap discontinuity, resulting in band offset. Thus, the carrier recombination probability increases in the vicinity of p/i interface because of high defect density and short carrier lifetime. Aided by optically calibrated simulations and with the support of experimental results, this study shows that a wide band gap thin undoped a-SiO:H buffer layer with higher photoconductivity reduces the band-gap offset and minimizes the recombination of photogenerated charge carriers at the defect-rich p/i interface. It has also been found that the a-SiO:H buffer layer augmented the electric field inside the device. As a result, the overall performance of the a-Si:H-based single junction solar cell has significantly improved. By employing a ∼5 nm thick a-SiO:H buffer layer, the blue response of the cell has been improved, resulting in 7.34% and 18.62% enhancement in fill factor (FF) and power conversion efficiency (η), respectively, as compared to the buffer-less cell.

Blue and violet defect levels mediated absorption hot spots in tapered ZnO nanorods toward improved photocatalytic activity

Tapered ZnO nanorods have been synthesized and found to have efficient photocatalytic properties owing to a large number of native defect sites arising from oxygen non-stoichiometry. The estimation of defect states was carried out using photoluminescence spectroscopy. Visible light-driven photocatalytic activity of the prepared ZnO nanorods was evaluated by measuring the photodegradation of two widely used industrial organic pollutants, viz. rose bengal and methylene blue. Investigation of electric field profile of the tapered ZnO nanorods revealed the generation of huge absorption hot spots in the visible region, indicating better light trapping in tapered ZnO nanorods than the non-tapered structure.

A simulation study of p-i-n amorphous silicon photovoltaic cell using ZnO nano rods

Thinning down the active absorber layer is the current trend in solar cell technology. The thinner absorber layer has two main advantages (i) it reduces the material consumption and (ii) minimizes the time and energy required in production. For thin film silicon (Si) technology, thinning down the absorber layer is of particular interest since the device throughputs of vacuum deposition systems as well as the stability of the devices are significantly enhanced. The 3D nanorod structure in thin-film photovoltaics has got much attention due to their enhanced light trapping capability, and it also requires less thick active layer. The enhanced light trapping results in more efficient absorption of spectrum within the solar cell structure. This gives the higher short circuit current and hence higher power conversion efficiency. We have developed the ZnO nanorods on the glass substrate through galvanic cell based approach and designed a nanorod solar cell through numerical simulations using technology computer aided design (TCAD) tool. Numerical simulation shows that the highest conversion efficiency of 9.12% is obtained for the zinc oxide nanorod solar cell which is nearly 18.59% more than the planar a-Si:H solar cell with same absorber layer thickness.

Silicon heterojunction solar cells with novel fluorinated n-type nanocrystalline silicon oxide emitters on p-type crystalline silicon

A novel fluorinated phosphorus doped silicon oxide based nanocrystalline material have been used to prepare heterojunction solar cells on flat p-type crystalline silicon (c-Si) Czochralski (CZ) wafers. The n-type nc-SiO:F:H material were deposited by radio frequency plasma enhanced chemical vapor deposition. Deposited films were characterized in detail by using atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM), Raman, fourier transform infrared spectroscopy (FTIR) and optoelectronics properties have been studied using temperature dependent conductivity measurement, Ellipsometry, UV–vis spectrum analysis etc. It is observed that the cell fabricated with fluorinated silicon oxide emitter showing higher initial efficiency (η = 15.64%, Jsc = 32.10 mA/cm2, Voc = 0.630 V, FF = 0.77) for 1 cm2 cell area compare to conventional n-a-Si:H emitter (14.73%) on flat c-Si wafer. These results indicate that n type nc-SiO:F:H material is a promising candidate for heterojunction solar cell on p-type crystalline wafers. The high Jsc value is associated with excellent quantum efficiencies at short wavelengths (<500 nm).