Marek Lipinski

Reduction of surface reflectivity by using double porous silicon layers

Abstract The reduction of optical losses is one of the important factors to obtain high efficiency silicon solar cells. It is known that porous silicon can replace the antireflection coating and texturization of surfaces. In our work, we present investigation of double porous silicon (d-PSi) layer structure. The first macro porous layer was created in p-type mc-Si Baysix material. After n + –p junction formation by POCl 3 diffusion, the second porous silicon (PSi) layer in the upper part of n + emitter was made. We have obtained d-PSi structure with effective reflectance of 5.8%. Microstructure of PSi was determined by SEM and TEM investigations. The total reflectivity of the samples, as a function of the wavelength was measured using Perkin–Elmer Lambda spectrophotometer equipment with an integrating sphere.

Comparison of diffused layer prepared using liquid dopant solutions and pastes for solar cell with screen printed electrodes

Purpose The purpose of this study is comparison of the diffusion processes performed using the commercial available dopant paste made by Filmtronics and the original prepared liquid dopant solution. To decrease prices of industrially produced silicon-based solar cells, the new low-cost production processes are necessary. The main components of most popular silicon solar cells are with diffused emitter layer, passivation, anti-reflective layers and metal electrodes. This type of cells is prepared usually using phosphorus oxychloride diffusion source and metal pastes for screen printing. The diffusion process in diffusion furnace with quartz tube is slow, complicated and requires expensive equipment. The alternative for this technology is very fast in-line processing using the belt furnaces as an equipment. This approach requires different dopant sources. Design/methodology/approach In this work, the diffusion processes were made for two different types of dopant sources. The first one was the commercial available dopant paste from Filmtronics and the second one was the original prepared liquid dopant solution. The investigation was focused on dopant sources fabrication and diffusion processes. The doping solution was made in two stages. In the first stage, a base solution (without dopants) was made: dropwise deionized (DI) water and ethyl alcohol were added to a solution consisting of tetraethoxysilane (TEOS) and 99.8 per cent ethyl alcohol. Next, to the base solution, orthophosphoric acid dissolved in ethyl alcohol was added. Findings Diffused emitter layers with sheet resistance around 60 Ω/sq were produced on solar grade monocrystalline silicon wafers using two types of dopant sources. Originality/value In this work, the diffusion processes were made for two different types of dopant sources. The first one was the commercial available dopant paste from Filmtronics and the second one was the original prepared liquid dopant solution.

Spray-on glass solution for fabrication silicon solar cell emitter layer

Purpose The main aim of this study was a preparation development of dopant solution (DS) which can be deposited by a spray-on method and subsequently allows obtaining the n+ emitter layer with surface resistance in the range of 65-80 Ω−1. The intention of chosen spray-on method was to gain a cheaper way of dopant source deposition, compared to the commonly used methods, which is of particular importance for the new low-cost production processes. Design/methodology/approach This paper presents the sequence in producing a spray-on glass solution (DS) with very high concentration of phosphorus, which allows to perform diffusion doping at relatively low temperatures. DS contained deionized water, ethyl alcohol, tetraethoxysilane and othophosphoric acid. Findings The sequence in producing a DS was performed with respect to enabling the application to silicon wafers by spray-on method. Furthermore, the equations defined density and viscosity of DS in term of storage time were referred to determine the possibility of applying this solution by spray-on method. Besides, the dependence of the emitter surface resistance on the doping (diffusion) time was determined. Accordingly, optimal process conditions were specified. Originality/value The paper presents a new, so far unpublished composition of DS with very high concentration of phosphorus, which can be applied using a spray-on method. Moreover, original are also investigations respecting some properties of obtained DS relative to storage time.

Optimization of the optical parameters of TiOx antireflection layers deposited by a spin-on technique

Abstract The optical properties of TiO x layers deposited by a spin-on technique with different spin speesd and baked at different temperatures have been studieed with consideration to their applicability as highly efficient antireflection coatings (ARC) for silicon solar cells. Some cells have been fabricated and both their spectral response as well a I–V curves have been measured. Cells with a TiO x ARC layer show an increase in the conversion efficiency up to nearly 40% when compared to “bare” cells, mainly due to a large increase in the short-circuit current.

Influence of ITO layer application on electrical parameters of silicon solar cells with screen printed front electrode

Purpose The purpose of this paper was investigation and comparison of electrical and optical properties of crystalline silicon solar cells with ITO or TiO2 coating. The ITO, similar to TiO2, is very well transparent in the visible part of optical radiation; however, its low resistivity (lower that 10-3 Ohm/cm) makes it possible to use simultaneously as a transparent electrode for collection of photo-generated electrical charge carriers. This might also invoke increasing the distance between screen-printed metal fingers at the front of the solar cell that would increase of the cell’s active area. Performed optical investigation showed that applied ITO thin film fulfill standard requirements according to antireflection properties when it was deposited on the surface of silicon solar cell. Design/methodology/approach Two sets of samples were prepared for comparison. In the first one, the ITO thin film was deposited directly on the crystalline silicon substrate with highly doped emitter region. In the second case, the TCO film was deposited on the same type of silicon substrate but with additional ultrathin SiO2 passivation. The fingers lines of 80 μm width were then screen-printed on the ITO layer with two different spaces between fingers for each set. The influence of application of the ITO electrode and the type of metal electrodes patterns on the electrical performance of the prepared solar cells was investigated through optical and electrical measurements. Findings The electrical parameters such as short-circuit current (Jsc), open circuit voltage (Voc), fill factor (FF) and conversion efficiency were determined on a basis of I-V characteristics. Short-circuit current density (Jsc) was equal to 32 mA/cm2 for a solar cell with a typical antireflection layer and 31.5 mA/cm2 for the cell with ITO layer, respectively. Additionally, electroluminescence of prepared cells was measured and analysed. Originality/value The influence of the properties of ITO electrode on the electrical performance of crystalline silicon solar cells was investigated through complex optical, electrical and electroluminescence measurements.

Study of Silicon Nanoparticles Formation in Silicon Nitride

We present results of the study on the silicon nanoparticles formation in multilayer silicon nitride structures. These structures consist of pairs of stoichiometric silicon nitride dielectric layers (SiNx) and silicon rich nitride layers (SRN). Silicon nanocrystals precipitate from the SRN layer during annealing at high temperatures (1000 °C or 1100 °C). High resolution transmission electron microscopy has been applied for investigation of the nanocrystals formation. Surface photovoltage spectroscopy technique was used for the spectral characterization of prepared structures

Optical properties of multilayer silicon nitride structures with silicon quantum dots

In our study we report the investigation of nanostructures embedded in silicon nitride films deposited by RF plasma enhanced chemical vapor deposition (PECVD). The multilayer structure consisting of fifty near-stoichiometric silicon nitride layers followed by silicon–rich silicon nitride layers has been deposited and heated in 1100 °C in order to realize the quantum dot superlattice. The properties of the quantum dots are investigated using high resolution transmission electron microscopy (HRTEM) and spectroscopic ellipsometry. It has been observed that after annealing the photoluminescence that was previously observed in the sample is strongly suppressed. At the same time a new absorption peak in the dispersion of the extinction coefficient occurred almost at the same value of the wavelength. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical investigations of macro- and microporous silicon antireflection coating

The studies of undoped and p porous silicon -doped type micro and macro porous silicon (PS) prepared by chemical and electro-chemical etching are reported here. The optical reflectance and photoluminescence of samples obtained under different conditions have been investigated. The PS investigated samples exhibited photoluminescence (PL) and antireflection properties (ARS).

Screen-printed silicon solar cells with texturized and passivated emitter diffused from spin-on phosphorous source

Spin-on phosphorus diffusion source has been used for emitter formation in silicon solar cells. It is shown that commercially available phosphorosilicamer emulsion used for that purpose can be easily modified by adding alcohol solution of P2O5 thus allowing us to obtain junctions with different dopant profiles for the same process conditions. SIMS curves have been taken for several samples and compared with theoretical simulation of diffusion profile showing that diffusion driven from spin-on source may strongly differ from that carried out from classic POCl3 source. Results of some experiments on emitter passivation by simple dry oxidation are also presented.