7 research outputs found
Enhanced metal assisted etching method for high aspect ratio microstructures: Applications in silicon micropillar array solar cells
No full textA solar cell device, fabricated on high density array cylindrical pillars, enables photogenerated carrier collection in the radial direction, thus shortening the path length of the carriers reaching the junction. It also provides advantages over conventional planar junction solar cells, such as reduced surface reflectance and enhanced light trapping. In this study, highly ordered Si micropillars were fabricated by photolithography and metal assisted etching (MAE) methods. It is shown that the use of ethanol as a solvent during the etching process and increasing HF concentration in the MAE solution both improve the quality of the surfaces of the pillars. Micropillars with smooth sidewalls and a high aspect ratio were obtained in this way. Solar cells with a radial junction were then fabricated on these micropillars. Standard doping, SiO2/SiNx passivation, and metallisation steps were carried out for the fabrication of solar cells with different micropillar lengths. A significant decrease in reflectance values was observed as the micropillar length increased, as expected. Solar cell short circuit current density (J(SC)) and efficiency (eta) of the solar cells tended to increase with micropillar length up to 11.5 mu m and then decrease due to increased surface recombination. The maximum efficiency achieved in this study is 17.26%
Hydrogen thermal activation of defects enabling firing stable Poly-Si based passivating contacts for TOPCon solar cells
No full textPassivating contacts based on poly-Si/SiOx also referred to as TOPCon (tunnel oxide passivated contacts) have substantially improved the performance of crystalline silicon (c-Si) solar cells. Hydrogenation in TOPCon has the utmost importance for achieving high quality surface passivation and enhanced solar cell performance. In this work, the hydrogenation mechanism and high-temperature fast firing behavior of phosphorus-doped TOPCon structures, on textured crystalline Si; coated with ALD–AlOx, PECVD–SiNx, and AlOx/SiNx stacks, are investigated. Using hot plate annealing series, our results show that thermal activation for hydrogenation is required for TOPCon/AlOx, while the hydrogenation is already activated for TOPCon/SiNx. For AlOx, activation energies (EA) are calculated in the 0.28 – 0.52 eV range, implying that hydrogenation is reaction limited rather than bulk diffusion of hydrogen atoms. The effect of TOPCon layers (SiOx and poly-Si thickness, ex-situ phosphorus diffusion, AlOx/SiNx) is explored. Among all, SiOx is the most critical factor affecting the firing stability. The firing stability is achieved for TOPCon/1.2 nm SiOx with iVOC of 720.6 mV and J0S=3.03 fA/cm2 while excellent passivation with iVOC of 735.1 mV and J0S=2.73 fA/cm2 are not maintained in TOPCon/1.6 nm SiOx after fast firing. The reason for this stability difference is explained by the fact that higher number of interfacial defects in 1.2 nm SiOx is beneficial for preventing blister formation during fast firing
Light Trapping by Micro and Nano-hole Texturing of Single-crystalline Silicon Solar Cells
No full textAbstractThe efficiency of a solar cell strongly depends on the interaction between the incoming light beam and the surface of the device. Any process enhances light-surface interaction increases absorption probability of the light; thus, improves generated current, in turn. Generated current could be improved either by light trapping or by increased device thickness. Considering fabrication costs and recombination losses, mechanically thin optically thick wafers are being focused on in terms of light trapping properties. Surface texturing among the other methods is an effective and more lasting technique in reducing reflections and improving light trapping. In order to maximize the absorption of light and the efficiency of the cell, various light trapping schemes have been proposed so far. In this study, texturing silicon (Si) wafer surface with periodic holes using two top-down fabrication techniques: Metal Assisted Etching (MAE) and Reactive Ion Etching (RIE) was focused on. Following the design of optical masks with patterns of different hole sizes and distributions, hole-textured surfaces with dimensions varying from micron scale to submicron scale were fabricated using both etching techniques. Hole-textured surfaces with desired hole depth values could be successfully fabricated. It was observed that surface having periodic holes with 4μm diameter, 5μm gap between holes and 8μm depth could result in 15.7% efficiency
Enhanced Passivation Properties of a-Si:H and Reactive ITO Sputtering for SHJ Solar Cells
No full textEnhancement of the conversion efficiency of silicon solar cells is crucial for the improvement of renewable electricity resources. The device properties such as minority carrier lifetime, series resistance, contact resistance and optical properties should be improved simultaneously to achieve higher photo conversion efficiencies. We use industry compatible processes flow to fabricate large-area silicon heterojunction (SHJ) solar cells combined with reactive ITO sputtering. The passivation properties of a-Si:H layer was improved by hydrogen plasma treatment resulting in a lower interface defect density and higher "H" content in the deposited thin a-Si:H layer. Moreover, carrier density, mobility and resistivity of ITO layer was analyzed and the best deposition condition of ITO is integrated to SHJ solar cell process sequence. Contact resistivity between ITO and low temperature silver paste was decreased by optimized drying and curing temperature parameters. In large- area SHJ solar cell, we have achieved conversion efficiency of 20.8%
A Study on Tetragonal-star Like Shaped Inverted Pyramid Texturing
No full textSurface texturing is one of the key process steps in solar cell fabrication. For an ideal surface texturing, surface recombination should be kept as low as possible while the light trapping property is improved. The formation of a random inverted pyramids is a good candidate with its improved light trapping properties compared to standard upright pyramid texturing and its reduced surface roughness compared to nanowire texturing resulting in reduced surface recombination velocity. In this work, we investigate a single step, lithography-free, Cu-assisted inverted pyramid texturing resulting in significantly reduced surface reflection on p-type Cz-Si. With the help of randomly distributed star-shaped inverted pyramid texturing on p-type Si, the weighted average reflection was reduced to 3% for p-type Si between 400-1000 nm. As a first cell trial, standard Al-BSF cells were fabricated using industrial process tools on p-wafer with star-shaped IPs. The low-cost, effective and repeatable nature of the developed single-step etching process has a high potential to replace surface texturing steps in the large-scale solar cell production cycle. Due to the implantation of star-shaped inverted pyramids to Al-BSF Si solar cell fabrication, short circuit current density was improved by more than 3.5%, resulting in 39.1mA/cm(2)
CZTSSe thin films fabricated by single step deposition for superstrate solar cell applications
No full textWOS: 000472079200036The focus of this study is the characterization of Cu2ZnSn(S,Se)(4) (CZTSSe) thin films and fabrication of CZTSSe solar cell in superstrate configuration. In this work, superstrate-type configuration of glass/ITO/CdS/CZTSSe/Au was entirely fabricated by totally vacuum-based process. CZTSSe absorber layers were grown by RF magnetron sputtering technique using stacked layer procedure. SnS, CuSe and ZnSe solid targets were used as precursors and no additional step like the selenization process was applied. The structural and morphological properties of deposited CZTSSe layers were analyzed using X-ray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy analysis (EDS) measurements. The optical and electrical properties of the CZTSSe thin films were investigated by UV-Vis spectroscopy, Hall-Effect and photoconductivity measurements. In addition, the device performance of the fabricated superstrate solar cell was examined.Middle East Technical University BAPMiddle East Technical University [GAP-105-2018-2755]This work was financed by Middle East Technical University BAP under Grant No. GAP-105-2018-2755
Slicing crystalline silicon wafer by deep subsurface laser processing and selective chemical etching
No full textDate of Conference: 23-27 June 2019Conference Name: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019In this work, we demonstrate use of laser-induced silicon slicing (LASIS) technique to fabricate crystalline silicon (c-Si) slices [1]. In LASIS method, a nanosecond-pulsed fiber laser operating at 1.55 μm wavelength, focused deep in Si subsurface induces structural modifications near the focal point due to multiphoton absorption. The raster scan of the focal position inside of the sample, positioned in cross-sectional plane with respect to laser beam, produces a quasi-2D modified Si region. The modified Si region is then etched by cupper nitrite (Cu(NO 3 ) 2 )-based selective chemical etchant which selectively targets the laser-modified regions. In order to achieve high etch rate, smooth and defect-free surface; different concentrations of etchant components and etch durations were investigated.EPS Young MindsQuantum Electronics and Optics Divisio
