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The wet oxidation method could gently reduce the dislocation and improve impurities getter efficiency in the process of oxidizing PRL to PSG. Although wet oxidation could cause some damage, the final result (PCE) is still improved.

Dopant-free carrier-selective contacts based on metal compounds have attracted considerable attention for high-efficiency crystalline silicon solar cells. In this work, the feasibility of using molybdenum oxynitride (MoOxNy) as an electron-selective contact layer in n-type crystalline silicon ( n-Si) solar cells has been demonstrated. With the increase in the N2:Ar ratio during the sputtering process, the work function of a MoOxNy film decreases from 4.57 to 4.26 eV, which is advantageous for the MoOxNy film to be an electron transport layer. An efficiency of 18.0% has been achieved in n-Si based solar cells using a full-area MoOxNy contact for electron extraction, featuring a high fill factor of 84.6%.

Lasers are frequently used to locally open dielectric layers for contacting the front or rear side of advanced silicon wafer solar cell architectures. For reasons of cost, laser processes are usually carried out in ambient environment, which inevitably leads to the oxidation of silicon. In order to achieve maximum solar cell efficiency, the laser processing has to be optimized thoroughly. The current research only focuses on minimizing laser-induced defects in silicon. However, our investigation shows another side effect of laser ablation, i.e., laser-induced oxidation, which is often neglected and undesirable for the subsequent metallization process. In this paper, we investigated the impact of laser-induced oxidation, which is caused by laser ablation in air, on the performance of silicon wafer solar cells. We show that by applying a postlaser etching step, laser-induced defects and oxide film can be removed effectively, providing improved conditions for the subsequent metallization process.

Tissue architecture plays critical roles in the physiological functions of blood vessels. Surface-patterned films are promising to replicate cellular alignment as in the native vessels. However, for vascular tissue engineering (TE) applications, the current surface-patterned films lack structural support for the myoendothelial communications between tunica media and intima. Herein, we report the development of direct microperforation using a femtosecond laser on surface-patterned films for the native-like architecture reconstruction of blood vessels. Poly(ε-caprolactone) (PCL) thin films were surface-patterned with anisotropic microridges/grooves. Direct femtosecond laser ablation further resulted in microscale through-holes for the PCL films, without invasive thermal damage to the ridges/grooves on the nonprocessed surface. Laser fluence and pulse number were observed to significantly influence the microperforation on both hole quality and dimension. The PCL films after direct femtosecond laser microperforation exhibited improved flexible properties, without sacrificing the yield stress. Meanwhile, direct femtosecond laser microperforation resulted in PCL films with hydrophilic permeability to transport nutritional/signaling biomolecules and allowed for heterocellular protrusion ingrowth into the through-holes for physical myoendothelial contacts. Small-diameter vascular TE scaffolds based on the as-fabricated PCL films could enable a hybrid vascular wall construction with aligned stromal multilayers and a confluent endothelium similar to those of the native vascular tissue. These results showed that direct femtosecond laser microperforation could be a reliable approach for producing biomimetic films with through-holes. The developed vascular TE scaffolds with microridges/grooves and through-holes have the potential to offer structural support for vascular architecture reconstruction with the native-like stromal and endothelial components.

For high-efficiency silicon wafer solar cells, Auger recombination is becoming one of the most important efficiency limiting factors. For this purpose it is desirable to be able to use different Auger recombination parameterisations in advanced computer simulations. In this paper we present a method to implement arbitrary Auger parameterisations in the software package Sentaurus TCAD, enabling two- and three-dimensional simulation of solar cells using different Auger parameterisations. As examples, we implemented and investigated three different Auger parameterisations (proposed by Altermatt et al., by Kerr and Cuevas, and by Richter et al.) from the literature. For verification, we simulate Auger lifetimes for different doping densities and injection levels in crystalline silicon. The simulated Auger lifetimes are found to agree well with analytical solutions (differences less than 0.001 %). We then employ the three different Auger parameterisations for fitting measured effective lifetime curves of both $$n$$ n -type and $$p$$ p -type float-zone silicon lifetime samples and show which models are applicable under which conditions. We further compare the difference between the three Auger parameterisations by simulating characteristics of a screen-printed aluminium local back surface field silicon wafer solar cell. The simulation results agree well with the characterisation results. We find that the choice of Auger parameterisation can lead to significant differences in the predicted solar cell behaviour under one-Sun illumination. We demonstrate that different Auger parameterisations may result in significant differences in the blue response, by simulating a heavily doped emitter of an aluminium local back surface field silicon wafer solar cell.

Aluminium local back surface field (Al-LBSF) cells are currently being investigated for the next generation of high efficiency industrial silicon wafer solar cells. These Al-LBSF solar cells feature passivating dielectric layers with local contact openings at the rear side of the cell. These local contact openings can be made by inkjet printing, laser ablation or mechanical scribing. Cell efficiencies of up to 19.0% have been achieved for screen-printed p-type Al-LBSF solar cells at SERIS, whereby the dielectric layer was locally opened by laser ablation. This paper reports on the optimisation of the laser process for this kind of solar cell by various characterisation techniques. Optical microscopy and scanning electron microscopy (SEM) are used to determine the degree of ablation of the dielectric layers and to examine the heat affected zone. Photoluminescence measurements are used to study if the electronic quality of the underlying silicon is affected by laser dielectric ablation. We demonstrate that similar solar cell efficiencies can be obtained using either a nanosecond (ns) or a picosecond (ps) laser for the laser ablation process, with the ns laser being an industrially more mature technology. Post-laser etching for laser-induced damage removal is found to be a crucial step to improve the efficiency of those cells which have their contact openings formed with the ns laser.

Presently, large-area high-efficiency (> 19%) screen printed p-type silicon solar cells are dominated by the aluminium local back surface field (Al-LBSF) technology. However, all those cells were fabricated with tube diffused emitters. Inline diffusion, using phosphoric acid as the dopant source, offers potentially low-cost emitter formation for p-type silicon wafer solar cells. To achieve higher efficiencies for these solar cells, the authors have applied a new Si etch solution to remove the dead layer of the inline diffused emitter. Efficiencies up to 18.3% were obtained for standard Al back surface field (Al-BSF) solar cells. In this work, the same etch-back process was applied to Al-LBSF devices. We report a maximum efficiency of 19.0%, an average batch efficiency of 18.9% (± 0.1% StDev), and a maximum open-circuit voltage of 640 mV for the cells, using industry-grade p-type 6 inch wide pseudosquare Cz mono-Si wafers. These results indicate that inline-diffused emitters can be used in high-efficiency silicon wafer solar cells.

Silicon wafer solar cells with a local back surface field (“LBSF”) formed by aluminium are currently intensively investigated for industrial application. The non-metallised rear surface regions of this structure are passivated by a dielectric film, whereby this film receives line or point openings for contact formation. In this work we report on Al-LBSF solar cells with thermally evaporated and screen-printed Al as the rear metal and screen-printed silver as the front contact. The interaction of Al and the locally opened dielectric film is investigated in detail, using techniques such as photoluminescence imaging and scanning electron microscopy. The impacts of the laser patterns used for opening of the dielectric film and void formation at the rear contact are investigated.

Surface enhanced Raman spectroscopy (SERS) has been widely investigated as an effective technique for low-concentration bio-chemical molecules detection. A rapid two-step approach to fabricate SERS substrates with high controllability in ambient air is developed. Dynamic laser ablation directly creates microgroove on the Si substrate. Meanwhile, nanoparticles are synthesized via the nucleation of laser induced plasma species and the air molecules. It configures the Si surface into four different regions decorated with nanoparticles at different sizes. With Ag film coating, these nanoparticles function as hotspots for SERS. Microsquare arrays are fabricated on the Si surface as large-area SERS substrates by the laser ablation in horizontal and vertical directions. In each microsquare, it exhibits quasi-3D structures with randomly arranged and different shaped nanoparticles aggregated in more than one layer. With Ag film deposition, uniform SERS signals are obtained by detecting the 4-methylbenzenethiol molecules. The SERS signal intensity is determined by the size and shape distributions of the nanoparticles, which depend on the laser processing parameters. With the optimal laser fluence, the SERS signals show a uniform enhancement factor up to 5.5 × 10(6). This provides a high-speed and low-cost method to produce SERS substrates over a large area.

Pulsed laser ablation is increasingly being applied to locally open the rear dielectric layer of advanced silicon wafer solar cell structures, such as aluminum local back surface field solar cells. We report that the laser ablation process on the rear surface of the solar cell at a relatively low laser fluence can cause undesirable spallation at the front surface which is textured with random upright pyramids. This phenomenon is attributed to the enhancement of the surface spallation effect by up to 3 times due to the confinement of the pressure waves at the tips of these random pyramids. Laser ablation at different laser focus positions and laser fluences is carried out to achieve optimized laser processing of the solar cells.

The rear surface of industrial p-type Cz wafers with a homogeneous n+ diffused emitter on the front was coated with a dielectric stack consisting of AlO x (40 nm) and a SiN x capping layer (100 nm), all deposited by plasma-enhanced chemical vapor deposition. Subsequently, the dielectric stack was locally opened using either laser ablation or inkjet printing. Three printing conditions with various pitch distances and number of inkjet printed layers were used and their impact on the solar cell efficiency investigated. A champion solar cell efficiency of 18.0% was achieved for a 125-mm pseudo-square, screen-printed Al-LBSF cell with inkjet-opened rear dielectric layer, while reference Al-LBSF cells with laser-opened rear dielectric layer achieved 17.6% champion cell efficiency.

Enhancement of pulsed laser ablation can be achieved in acetic acid as an environmentally friendly liquid. This paper evaluates microholes and textured features induced by a nanosecond pulsed laser under different processing circumstances. The microholes are fabricated by laser drilling in acetic acid and found to be 100% deeper than in air. The textured features achieved in the liquid demonstrate a higher content of Copper and a lower content of Oxygen. The improvement of laser ablation efficiency in the liquid is attributed to the strong confinement of plasma plume accompanying with shockwave and cavitation bubbles. Meanwhile, the laser enhanced chemical etching by the weak acid plays a critical role.