Ayu Wazira Azhari

Synthesis and characterization of self-assembled, high aspect ratio nm-scale columnar silicon structures

The aim of this work is to synthesize nm-scale columnar structures in Si principally for solar cell applications. These structures are also desirable as templates for heteroepitaxial growth of SixGe1-x. A nanostructured layer is instrumental in facilitating pseudomorphic heteroepitaxial growth of SixGe1-x layers since it can help reduce lattice mismatch as well as thermal expansion mismatch, thus, leading to Si-based high efficiency solar cells at lower cost. A simple yet promising method was chosen to synthesize randomly distributed, nm-scale columnar structures. This metal assisted chemical etching (MACE) technique uses metal-induced oxidation of silicon to anisotropic trenches. Preliminary results indicate that nm-scale columns as characterized by field emission scanning microscopy (FE-SEM) consist of fine pores running parallel to the wafer surface and deeply etched anisotropic columns perpendicular to the surface. All etching work was carried out on (100) orientation Si wafers. Results indicate strong dependence on solution concentration both in terms of profile and etch rate. Optical characterization based on spectral reflectance and transmission measurements have been employed in characterizing the nm-scale surfaces. Initial studies indicate low reflectance and high absorption with increasing depth of the nanostructures.

Characterization of perovskite layer on various nanostructured silicon wafer

Crystalline silicon (c-Si) solar cell dominates 90% of photovoltaic (PV) market. The c-Si is the most mature of all PV technologies and expected to remain leading the PV technology by 2050. The attractive characters of Si solar cell are stability, long lasting and higher lifetime. Presently, the efficiency of c-Si solar cell is still stuck at 25% for one and half decades. Tandem approach is one of the attempts to improve the Si solar cell efficiency with higher bandgap layer is stacked on top of Si bottom cell. Perovskite offers a big potential to be inserted into a tandem solar cell. Perovskite with bandgap of 1.6 to 1.9 eV will be able to absorb high energy photons, meanwhile c-Si with bandgap of 1.124 eV will absorb low energy photons. The high carrier mobility, high carrier lifetime, highly compatible with both solution and evaporation techniques makes perovskite an eligible candidate for perovskite-Si tandem configuration. The solution of methyl ammonium lead iodide (MAPbI3) was prepared by single st...

Response Surface Methodology (RSM) in Fabrication of Nanostructured Silicon

In this paper, a respond surface methodology (RSM) model has been developed using three levels Box-Benkhen experimental design (BBD) technique to study the influence of several metal-assisted chemical etching (MACE) process variables on the properties of nanostructured silicon (Si) wafer. Five process variables are examined i.e. concentrations of silver (Ag), hydrofluoric acid (HF), deposition time, H2O2 concentration and etching time as a function of etching rate. Design-Expert® software (version 7.1) is used in formulating the RSM model of five factors with 46 experiments. A regression quadratic model is developed to correlate the process variables where the most significant factors are identified and validated using analysis of variance (ANOVA). The model for etching rate is found to be significant with R2 of 0.8, where both Ag concentrations and etching time are the major influence.

Synthesis of Chlorophyll Thin Film from Noni Leaves via Dip Coating Process

Chlorophyll is a green pigment responsible for the photosynthesis processes that occur in the green leaf. The chlorophyll pigment can be extracted from green leaf using simple solvent solution as a function of solar energy conversion. Dip coating onto glass slide was applied to produce a thin film of Noni leaves chlorophyll. The Noni leaves chlorophyll thin films were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and ultra violet visible (UV-Vis). The micrograph of SEM shows that the shapes were found in various shapes. The UV-Vis analysis revealed that the extracted chlorophyll had three absorbance spectra at 433 nm, 464 nm and 664 nm. These show that the extracted chlorophyll contains both chlorophyll-a and chlorophyll-b in the mixture.

Role of micro and nanostructures in enhancing near IR optical absorption in Silicon

Role of micro and nanostructures in enhancing IR transmission in Si wafers has been investigated. Based on feature dimensions, incident light interaction can be described in terms of: (a) geometrical optics for wavelengths significantly smaller than surface dimensions, (b) diffractive optics for wavelengths comparable to surface features, and (c) physical optics for wavelengths substantially larger than surface features. Randomly distributed features in micro and nanoscale regimes were fabricated on identical Si wafers. A simple IR optical transmission system based on InGaAs photodetector and monochromator was developed for optical measurements. Optical transmission near the bandgap was substantially reduced by randomly distributed nanostructures likely attributed to diffractive optics. At the conference, details of several structures along with their reflection and transmission measurements will be presented in order to determine optimum surfaces for lowest transmission near the bandgap.

Optical characterization of Si x Ge 1−x films grown on nanostructured Si substrates

High quality Ge and SixGe1-x films grown on Si substrates are attractive for a wide range of applications in optics, optoelectronics, and high efficiency solar cells. In this study, heteroepitaxial growth of Ge on nanostructured Si surfaces has been investigated. Thermally evaporated amorphous Ge films are vacuum-deposited and crystallized by thermal annealing at 1000 °C. Scanning electron microscope (SEM), spectroscopy (RS), infrared (IR) transmission, and Raman methods are used to characterize amorphous and crystalline Ge films. SEM analysis reveals presence of dominant features including cracks, microscopic roughness, and islands. RS exhibits strong multiple peaks attributed to crystalline structures related to Si-Ge at ~ 444 cm-1 and Ge at 300 cm-1; narrow and stronger peaks are observed in thermally annealed films. A comparison of IR transmission measurements in 900-1700-nm spectral range shows that amorphous film absorption is significantly higher than that of crystalline films consistent with respective bandgaps. A more detailed analysis including EDX and XRD measurements will be presented at the conference.

Investigation of XeF 2 dry etching for contact isolation of screen printed IBC solar cell

We demonstrated the use of Xenon Difluoride (XeF2) plasma less vapor etching for isolation of n and p regions in screen-printed interdigitated back contact (IBC) solar cell. The fabrication process is free from lithography process and carried out using standard conventional silicon solar cell equipment. A p-type CZ wafer was used as the starting material and POCl3 furnace was used to form the emitter. Silver and Aluminum pastes were screen printed to form emitter and base contacts respectively. An automated XeF2 vapor etching system was used for blanket etching of doped region between emitter and base metal contacts. Solar cell LIV response was measured as a function of XeF2 etching. Open-circuit increased as a function of XeF2 etching indicating removal of doped silicon; however, solar cell response was poor presumably due to large un-passivated, junction-free regions between positive and negative contacts. In order to improve performance, an extra alignment step is needed to etch small regions only.

Numerical analysis of bifacial solar cell using PC1D software

Computer-based simulations play a critical role in the design, development, and functionality of solar cells. Device modeling techniques substantially reduce the time and costs through optimization of process steps, choice of materials, and wafers. In this study, bifacial solar cell devices have been modeled using actual physical device configurations. In this study, a detailed description of npp+ bifacial solar cell based on PC1D simulations has been carried out. The structure of npp+ was selected for all simulations due to excellent results obtained from this type of solar cell. The npp+ configuration is also the simplest, most widely used solar cell, is simple to fabricate, and can be adapted for all types of solar cells. The efficiencies obtained from this design were 16.42 % and 14.18 % for front and back surfaces respectively. These simulations suggest that rear surface efficiency is a sensitive function of minority carrier lifetime, BSF doping level, and surface recombination velocity. Simulations results adequately explained performance of Al BSF bifacial solar cells fabricated in the laboratory.