Chandra Bhal Singh

Application of SixNy:Hz (SiN) as index matching layer in a-Si:H thin film solar cells

The difference in refractive indices of glass substrate and transparent conducting oxide (TCO) electrode causes optical reflection in thin film solar cells, which results in lower absorption of light for devices. An anti-reflection layer between glass and TCO is required to reduce the loss of light due to optical reflection. Silicon nitride (SixNy:Hz) films have shown antireflection property. The refractive index of SixNy:Hz films can be engineered by changing the silicon or nitrogen content in the film. Here, we report the optimization of refractive index of SixNy:Hz to achieve a value between refractive index of glass (1.5) and TCO film (2.0). SixNy:Hz films have been deposited in a RF-plasma enhanced chemical vapour deposition system operating at a frequency of 13.56 MHz. The substrate temperature was fixed at 300 °C. Fourier transform infrared analysis has been used to determine the nature of Si-N, N-H, and Si-H bonding in the films. Refractive index of films has been measured using spectroscopic elli...

Raman spectroscopy study of growth of multiwalled carbon nano-tubes using Plasma Enhanced Chemical vapour depositon

Here, we report the study of growth of CNTs using pulsed DC Plasma Enhanced Chemical Deposition (PECVD) process. Pulsed DC PECVD is employed as it provides enhanced control on arcing and uniformity over large area and thus control on length, diameter and positioning of CNTs. High yields of Multi-Walled Carbon nanotubes with diameters ranging from 40 to 100 nanometers are synthesized by plasma enhanced chemical Vapour deposition system. A layer of Titanium (50 nm) is used as buffer layer and a layer of Nickel (∼10 nm) is used as catalyst layer. Effect of Temperature, growth pressure and acetylene (C2H2) concentration on the synthesis of CNTs is studied. CNTs are characterized by Secondary Electron Microscopy (SEM) and Raman spectroscopy. Uniform CNTs growth observed at growth temperature 700 °C and 800 °C. Raman spectroscopy of CNTs shows that the strength of D-band (Defect-induced band) relative to G-band (Graphite-related optical band) decreases as the growth temperature increases which indicates the crystalline, defects free, uniform diameter and length of aligned CNTs. From temperature 700°C to 800°C, Up-shift in D-band indicates the increase in diameter of CNTs while up-shift in G-band may because of chemical doping in tubes. Downshift in G-band.

Effect of ZnO:Al Thickness on the Open Circuit Voltage of Organic/a-Si:H Based Hybrid Solar Cells

Hybrid solar cells are based on the concept of using both organic and inorganic materials for fabrication of devices. Hybrid solar cells, based on a heterojunction between inorganic electron acceptor layer and organic donor layer, has been fabricated. Effect of electron transport layer on open circuit voltage () of hybrid solar cells was investigated. Hybrid solar cells were fabricated using amorphous silicon as main absorbing layer and as electron acceptor layer while using copper phthalocyanine (CuPc) as the donor materials. Al doped ZnO layer was used as buffer layer between ITO and a-Si:H to prevent ITO from reacting with silane gas during plasma enhanced chemical deposition (PECVD) process. ZnO:Al thin film also acts as electron transport layer. The open circuit voltage of hybrid solar cells studied with varying the thickness of ZnO:Al layer. was increased from 0.30 volt to 0.52 volt with increasing the thickness of ZnO:Al layer from 15 nm to 45 nm. The poor interface between inorganic (a-Si:H) and organic layers may be a possible reason for low fill factor and low photocurrent in hybrid solar cells.

Effect of boron doping on optical and electrical properties of p-type a-Si∶H films for thin film solar cells application

We report the effect of boron doping on optical and electrical properties of p-type a-Si:H films. The p-type a-Si:H thin films have been deposited by RF-PECVD system varying the diborane flow rate from 5 sccm to 9 sccm. Enhancement in deposition rate from 30.3 nm/min to 33.6 nm reported with increasing diborane gas flow rate. Change in band gap, refractive index and Urbach energy with varying doping level is studied. An increase in dark conductivity is reported with increasing boron concentration. Solar cells fabricated with 4.63% efficiency.

Raman and FTIR Studies on PECVD Grown Ammonia-Free Amorphous Silicon Nitride Thin Films for Solar Cell Applications

Ammonia- (NH3-) free, hydrogenated amorphous silicon nitride (a-SiNx:H) thin films have been deposited using silane (SiH4) and nitrogen (N2) as source gases by plasma-enhanced chemical vapour deposition (PECVD). During the experiment, SiH4 flow rate has been kept constant at 5 sccm, whereas N2 flow rate has been varied from 2000 to 1600 sccm. The effect of nitrogen flow on SiNx:H films has been verified using Raman analysis studies. Fourier transform Infrared spectroscopy analysis has been carried out to identify all the possible modes of vibrations such as Si–N, Si–H, and N–H present in the films, and the effect of nitrogen flow on these parameters is correlated. The refractive index of the above-mentioned films has been calculated using UV-VIS spectroscopy measurements by Swanepoel’s method.

Effect of Substrate Temperature Variation and Tartarization on micro-Structural and Optical Properties of Pulsed DC Sputtered Hydrogenated ZnO: Al Films

In this work, hydrogenated ZnO: Al films have been deposited on glass substrate by pulsed dc magnetron sputtering unit at various substrate temperatures. The effect of substrate temperature on microstructural and optical properties of deposited films in hydrogen and Argon ambient was analyzed. Transmittance of films improved for films deposited at higher substrate temperature and reflectance decrease which is good as transparent conducting oxide for solar cells application. The wet chemical etching of hydrogenated films was performed to improve the light trapping in films. Films deposited at 250 °C showed lower resistivity and higher roughness after wet chemical etching than films deposited at room temperature. Films deposited at 150 °C shows better films quality as well as lower resistivity than films deposited at room temperature and 250 °C. This suggests that film’s microstructural, optical and electrical properties behave differently in hydrogen gas ambient and hydrogen improve films quality and conductivity at lower temperature.

Effect of Si, Sc, Cr doping on the structural, optical and discharge characteristics of MgO thin films as protective layer for plasma display panels

We report the effect of Si, Cr, Sc doping in the crystalline structure, optical and discharge characteristics of MgO thin films. Silicon and multiple (Si, Cr, Sc) doped MgO thin films demonstrate higher secondary electron emission (SEE). Si doping with Cr and Sc doping in MgO films shows much higher SEE as compared to pure and only Si doped MgO films. The importance of optimum amount of Sc doping is seen in our study where SEE reduced with further increase in Sc doping. The structural attributes of MgO films are correlated to the observed changes in discharge characteristics in the context of varying amount of Si, Sc, and Cr doping.

Effect of temperature conditions on the emission of ion-induced secondary electrons from MgO films

We report that the vacuum annealing of MgO films at 225°C results in the removal of water based contamination and the secondary electron emission coefficient increases from 0.09 to 0.15. The effective secondary electron emission yield increases from 0.2 to 0.75 at 200 mbar chamber pressure, as temperature increases to 250 °C. The effective secondary electron emission yield at 200, 350 and 800 mbar pressure shows similar trend during the heating as well as cooling of the MgO sample. Thermionic emission, smaller surface band bending and the removal of impurities at high temperature are possible reasons for the increase in secondary electrons of MgO thin films.