Numerical Simulation Analysis of Ag Crystallite Effects on Interface of Front Metal and Silicon in the PERC Solar Cell

In the fabrication of crystalline silicon solar cells, the contact properties between the front metal electrode and silicon are one of the most important parameters for achieving high-efficiency, as it is an integral element in the formation of solar cell electrodes. This entails an increase in the surface recombination velocity and a drop in the open-circuit voltage of the solar cell; hence, controlling the recombination velocity at the metal-silicon interface becomes a critical factor in the process. In this study, the distribution of Ag crystallites formed on the silicon-metal interface, the surface recombination velocity in the silicon-metal interface and the resulting changes in the performance of the Passivated Emitter and Rear Contact (PERC) solar cells were analyzed by controlling the firing temperature. The Ag crystallite distribution gradually increased corresponding to a firing temperature increase from 850 ∘C to 950 ∘C. The surface recombination velocity at the silicon-metal interface increased from 353 to 599 cm/s and the open-circuit voltage of the PERC solar cell decreased from 659.7 to 647 mV. Technology Computer-Aided Design (TCAD) simulation was used for detailed analysis on the effect of the surface recombination velocity at the silicon-metal interface on the PERC solar cell performance. Simulations showed that the increase in the distribution of Ag crystallites and surface recombination velocity at the silicon-metal interface played an important role in the decrease of open-circuit voltage of the PERC solar cell at temperatures of 850–900 ∘C, whereas the damage caused by the emitter over fire was determined as the main cause of the voltage drop at 950 ∘C. These results are expected to serve as a steppingstone for further research on improvement in the silicon-metal interface properties of silicon-based solar cells and investigation on high-efficiency solar cells.

Investigation of the Screen-printable Ag/Cu Contact for Si Solar Cells Using Microstructural, Optical and Electrical Analyses

ABSTRACTIn a bid to further reduce the cost of the front Ag contact metallization in Si solar cells, Cu is the potential alternative to replace the Ag in the Ag paste. However, this requires an understanding of the contact mechanism of screen-printable Ag/Cu paste in Si solar cell through rapid thermal process. The pastes with different weight percent of Cu (0 wt%, 25 wt% and 50 wt%) were used and the Voc of the cells was reduced with the increasing weight percent of Cu. This is because the presence of Cu in the paste changed the microstructure of the Ag/Cu/Si contact through Cu doping of the glass frits and hence increasing the Tg of the glass. The increased Tg of the glass impeded the uniform spreading of the molten glass and resulted in poor wetting and etching of the SiNx, which impacted the contact as evident in ideality factor of less than unity. This also led to the formation of agglomerated Ag crystallites with features of 700 nm in length and 200 nm in depth, which is close to the p-n junction, of which depth is ∼300 nm. However, the interface glass layer acted as an effective diffusion barrier layer to prevent Cu atoms from diffusing into the Si emitter, which is quite remarkable for Cu not to diffuse into silicon at high temperature. Further investigation of the Ag/Cu contacts with the conductive AFM in conjunction with the SEM and STEM analyses revealed that the growth of Ag crystallites in the Si emitter is responsible for carrier conduction the gridlines as with the pure Ag paste.

Composite Electrodes of Activated Carbon and Multiwall Carbon Nanotubes Decorated with Silver Nanoparticles for High Power Energy Storage

Composite materials in electrodes for energy storage devices can combine different materials of high energy density, in terms of high specific surface area and pseudocapacitance, with materials of high power density, in terms of high electrical conductivity and features lowering the contact resistance between electrode and current collector. The present study investigates composite coatings as electrodes for supercapacitors with organic electrolyte 1.5 M TEABF4 in acetonitrile. The composite coatings contain high surface area activated carbon (AC) with only 0.15 wt% multiwall carbon nanotubes (MWCNTs) which, dispersed to their percolation limit, offer high conductivity. The focus of the investigations is on the decoration of MWCNTs with silver nanoparticles, where smaller Ag crystallites of 16.7 nm grew on carboxylic group-functionalized MWCNTs, MWCNT–COOH, against 27–32 nm Ag crystallites grown on unfunctionalized MWCNTs. All Ag-decorated MWCNTs eliminate the contact resistance between the composite electrode and the current collector that exists when undecorated MWCNTs are used in the composite electrodes. Ag-decorated MWCNT–COOH tripled the power density and Ag-decorated MWCNT additive doubled the power density and increased the maximum energy density by 6%, due to pseudocapacitance of Ag, compared to composite electrodes with undecorated MWCNTs.

The Role of Nano-crystallites on Conduction Mechanisms of Current Through Ag Gridlines of Si Solar Cells

ABSTRACTIn order to understand the impact of nano-crystallites on current transport mechanisms in screen-printed c-Si solar cells with lowly-doped emitter, Te-glass based Ag pastes with different transition temperatures (Tg) were used. The Te-glass with lower Tg showed lower Rc than the one with higher Tg due to the formation of nano-crystallites in the glass layer. These nano-crystallites enhance the conductivity of the glass and lead to higher fill factor (FF). The nature of these nano-crystallites was first identified by the Raman spectrometry and the peaks at 76 cm-1, 119 cm-1 and 145 cm-1 were corresponding to Ag2Te and PbTe. The conductive-AFM further confirmed the high conductivity of these nano-crystallites without pyramidal Ag crystallites, which means the current transporting from Si emitter to Ag gridlines is mainly through the nano-crystallites in the glass.

Firing and Contact Resistivity of Ag2O-Aided Pb-Free Silver Paste for Crystalline Silicon Solar Cells

The silver pastes containing Ag2O powder, Ag powder, α-terpineol, ethyl-cellulose and Pb-free glass were synthesized for crystalline silicon (c-Si) solar cells. It was found that α-terpineol assisted the decomposition of Ag2O powder and effectively lowered the decomposition temperature of Ag2O. Ag nanoparticles were produced during the decomposition of Ag2O, which helped to reduce the sintering temperature of the silver pastes. The Ag2O-aided silver pastes were fired on polycrystalline silicon solar cells at various temperatures, and large plate-shaped Ag crystallites appeared at the interfaces between the sintered pastes and the emitter, which ensured a good electrical contact. The contact resistivity of Ag2O-aided silver paste with an optimal ratio of Ag2O to Ag was lower than that of the paste with pure Ag powder. The lowest contact resistivity of Ag2O-aided Pb-free silver pastes sintered at 800°C was 0.029 Ω⋅cm2, which was close to that of commercial silver paste that contained Pb-based glass (0.026 Ω⋅cm2). The experimental data demonstrated that the addition of Ag2O reduced the contact resistance and promoted the sintering of Pb-free silver pastes, and Ag2O-aided Pb-free silver paste could be a promising candidate used for front-contact electrode of c-Si solar cells.

Green Synthesis of Silver Nanoparticles Using Apple Extract and Its Antibacterial Properties

Silver nanoparticles (AgNPs) were synthesized using apple extract as a reducing agent and aqueous silver nitrate as the precursor. The AgNPs formation was observed as a color change of the mixture from colorless to dark-brownish. The X-ray diffraction pattern confirmed the presence of only Ag crystallites, and the dynamic light scattering estimates the average sizes of the AgNPs to be 30.25 ± 5.26 nm. Furthermore, Fourier Transform Infrared as well as UV-vis spectroscopy identifies ethylene groups as the reducing agent and capping agent for the formation of the AgNPs. This green synthesis provides an economic, eco-friendly, and clean synthesis route to AgNPs. AgNPs in suspension showed activity against Gram-negative and Gram-positive bacteria with minimum bactericidal concentrations (MBCs) to be in the range from 125 μg/mL to 1000 μg/mL.

Microwave Synthesis of Nanosilver Colloidal Suspension for Anti-Bacterial Coating

This article reports a microwave-assisted route to synthesize nanosilver colloidal suspension and to deposit silver nanoparticles onto activated carbon fabrics (ACFs). The properties of the nanosilver suspension are characterized in terms of bacterial inactivation and growth inhibition. The metallic Ag nanocrystals with narrow size distribution are uniformly dispersed onto ACFs under the microwave irradiation of 1 min. Microwave irradiation is capable of heating up the reaction solution homogeneously, inducing uniform nucleation and rapid crystal growth to form the Ag crystallites. This work aims to elucidate how as-grown Ag nanoparticles affect the inactivation of Escherchia coli (E. coli) and how Ag-ACF surface inhibits the bacterial growth. The Ag colloidal suspension offers superior anti-bacterial ability against E. coli cells at a low concentration of 20 mg/L. Thus, the study has established a simple, efficient and effective process in the synthesis of both Ag colloidal suspension and Ag-ACF composite.

Kinetic Limitations in Two-and Three-Dimensional Growth

ABSTRACTKinetic limitations related to the Schwoebel-Ehrlich (SE) diffusion barrier are examined in two-(2D) and three-dimensional (3D) growth. It is shown that the realization of step instabilities in 2D growth, possibly caused by the SE barrier, may be hindered by other factors such as step permeability and the relative importance of diffusion and step attachment. Growth shapes of Ag crystallites are also determined that reveal the impact of kinetic limitations. Dramatic changes of growth shape caused by In codeposition suggest that surfactants can modify the 3D SE barrier.