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Cast-mono silicon material is interesting for its lower carbon footprint compared to Czochralski (Cz) monocrystalline silicon. However, solar cells fabricated using cast-mono (CM) silicon show lower performances. In this work, two routes to make cast-mono silicon advantageous over Cz silicon are considered. The first route is to further reduce carbon footprint of cast-mono silicon, by using Upgraded Metallurgical Grade silicon (UMG-Si) feedstock instead of Solar Grade silicon (SoG-Si) feedstock. TOPCon solar cells are fabricated using both feedstocks, and cast-mono growth technology, using industrial-type furnaces. Laboratory studies show that UMG-Si can result in efficiencies higher than solar cells made of SoG-Si when feeding the material to a CM crystallization process. But when compared to Cz, CM-UMG-Si TOPCon solar cells conversion efficiency values are still 0.5%abs lower. The second route is to take advantage of the TOPCon passivation layer (e.g., poly-Si) ability to getter metallic impurities, and thus improve the quality of cast-mono material. Several TOPCon sequences are tested and their effect on the carrier recombination properties of the device are studied. In the end, solar cells are fabricated and again, UMG-Si solar cells show better results than SoG-Si solar cells, with efficiency up to 22.65%, independently confirmed.

We present an analytical model for the internal resistance of passivated emitter and rear totally diffused (PERT) solar cells. First, we apply the model of Saint-Cast for the spreading resistance of a passivated emitter and rear cell (PERC) structure with line-shaped contacts. To account for the additional vertical current flow through the silicon wafer and the lateral current flow through the back surface field of a PERT structure, we add a parallel current path using common analytical expressions. We compare the analytical models with two-dimensional numerical simulations based on Quokka 3 and find deviations of less than 6% for the internal resistance. In addition, we compare the analytical model of the internal resistance of PERC and PERT solar cells with experimental data of the series resistance of PERC and PERT solar cells. [ABSTRACT FROM AUTHOR]

In this work, we analyse passivated emitter and rear cells (PERC), based on wafers made from seed manipulation for artificially controlled defects technique (SMART) monocrystalline silicon, magnetically grown and conventional Czochralski (mCz and Cz) silicon, and high‐performance multicrystalline (hpm) silicon. All wafers were processed identically except for the hpm wafers, which received an acidic texture instead of random pyramids. The energy conversion efficiency η of the SMART cells of 21.4 % is similar to the mCz cells (21.5 %) while being more than 1.9%abs higher than for the hpm cells. Furthermore, we here show for the first time that light‐ and elevated temperature‐induced degradation (LeTID) is mitigated in hpm, Cz and SMART PERC cells without significant losses in initial efficiency by an adapted fast‐firing process, incorporating slower firing ramps that can be used in industrial production. The cells that are fired with these ramps show no significant efficiency loss (1%rel<Δη<2%rel) during LeTID testing at 75°C and 0.15 suns illumination for 1100 h, while the reference fast‐firing process results in efficiency losses of 5%rel<Δη<6%rel due to LeTID. For Cz cells that have been treated to regenerate the boron–oxygen defect prior to LeTID testing, the maximum degradation was reduced from Δη≈3%rel to Δη≈1.5%rel. [ABSTRACT FROM AUTHOR]

In this publication, the activation and degradation of the passivation quality of plasma-enhanced chemical vapor deposited aluminum oxide (Al2O3) layers with different thicknesses (10 nm, 20 nm, and 110 nm) on crystalline silicon (c-Si) during long and high temperature treatments are investigated. As indicated by Fourier Transform Infrared Spectroscopy, the concentration of tetrahedral and octahedral sites within the Al2O3 layer changes during temperature treatments and correlates with the amount of negative fixed charges at the Si/Al2O3 interface, which was detected by Corona Oxide Characterization of Semiconductors. Furthermore, during a temperature treatment at 820 °C for 30 min, the initial amorphous Al2O3 layer crystallize into the γ-Al2O3 structure and was enhanced by additional oxygen as was proven by x-ray diffraction measurements and underlined by Density Functional Theory simulations. The crystallization correlates with the increase of the optical density up to 20% while the final Al2O3 layer thickness decreases at the same time up to 26%. All observations described above were detected to be Al2O3 layer thickness dependent. These observations reveal novel aspects to explain the temperature induced passivation and degradation mechanisms of Al2O3 layers at a molecular level like the origin of the negative fixe charges at the Si/SiOx/Al2O3 interface or the phenomena of blistering. Moreover, the crystal phase of Al2O3 does not deliver good surface passivation due to a high concentration of octahedral sites leading to a lower concentration of negative fixed charges at the interface. [ABSTRACT FROM AUTHOR]

We present two approaches for high‐accuracy aligning of patterning processes with each other when fabricating solar cells. We introduce the approaches on the example of two different patterning processes of which one is adjustable (laser process) and one is not adjustable (screen‐printing process). The basic idea is to measure the coordinates of the applied structures of each involved patterning process at discrete grid points with respect to a reference coordinate system. We chose the grid points such that they completely define the final cell pattern. Then, we adjust the grid point coordinates of one of the patterning processes (the laser process) according to the pattern of the other process (the screen‐printing process). The laser then performs the patterning by connecting the corrected grid points with each other in the desired direction. We perform the associated high‐precision measurement of the patterns' coordinates by using either a high‐precision offline coordinate measuring machine or a high‐resolution inline camera system with subsequent computer‐based data processing. The latter inline method enables high throughput and is, in turn, of great interest for mass production of solar cells. In this paper, we demonstrate the alignment procedure approaches on "pPassDop" solar cells by adjusting a locally applied laser process to the directly following screen‐printing step. This proof of principle includes both above‐mentioned methods for coordinate determination in separate cell batches. Our innovative alignment procedures so far demonstrated the successful matching of 40‐μm‐wide screen‐printed contact fingers to 70‐μm‐wide laser‐processed lines over the entire area of 6‐inch solar cells. [ABSTRACT FROM AUTHOR]

In this paper an analytical model of the effective recombination (Seff) on the back surface of locally contacted solar cell is developed. We justify this approach by first showing that the three-dimensional (3D) problem can be reduced to a one-dimensional (1D) problem by calculating Seff. The values of Seff calculated with our model and two existing models are compared to finite element simulations. A large range of cases from high to low scale structures, including variation in the surface recombination velocity at the passivated area are investigated. The model presented in this paper is in good agreement with finite element simulations. Existing models from literature are also compared to finite element simulations, showing some of their limitations. In addition, we propose a method, not restricted to dark conditions, that simulates the 3D locally contacted structures by means of two 1D simulations. [ABSTRACT FROM AUTHOR]

This work demonstrates the efficient optical and passivation properties provided by hydrogenated silicon nitride (SiNx:H) layers deposited in a lab‐scale atmospheric pressure plasma enhanced chemical vapor deposition (AP‐PECVD) reactor. By applying modulated low‐frequency plasma (200 kHz), homogeneous SiNx:H layers, with small variances in thickness w and refractive index n (Δw ≤ 2 nm; Δn ≤ 0.02), were achieved on a surface area of 45 × 55 mm2. The use of voltage amplitude modulation enabled discharge optimization and led to greatly enhanced SiNx:H film homogeneity and conformity in comparison with continuous plasma discharge conditions. Additionally, AP‐PECVD SiNx:H showed good thermal stability (Δw ≤ 1 nm; Δn ≤ −0.02) with low absorption coefficients (k ≤ 0.1 at 275 nm), demonstrating that such layers could act as efficient antireflective coatings. Furthermore, outstanding surface passivation properties were achieved after firing, both on n‐type FZ c‐Si substrates of standard 2.8 Ω.cm doping (τeff = 1.45 ms) and on highly doped 85 Ω/sq n+ emitters (j0e = 74 ± 2 fA.cm−2). Finally, AP‐PECVD SiNx:H thin films were tested on industrial passivated emitter and rear solar cell (PERC) architectures, where the potential of applying these layers both as efficient rear‐side capping layer and front‐side antireflective coating was demonstrated. The first lab‐scale 40 × 40 mm2 PERC solar cells featuring AP‐PECVD SiNx:H layers led to conversion efficiencies of up to 20.6%. These results pave the way for upscaling the dielectric barrier discharge lab‐scale reactor in an industrial in‐line process, which could provide low‐cost and high‐throughput SiNx:H capping and antireflective layers. [ABSTRACT FROM AUTHOR]

The loss analysis of state-of-the-art p-type Czochralski-grown silicon passivated emitter and rear solar cells (PERC) fabricated in a manner close to industrial production is presented in this paper. The 6-inch solar cells are featuring a homogeneous emitter on the front side, an Al2O3 passivation layer and local contacts on the rear side. The peak energy conversion efficiencies obtained are 21.1% for a standard antireflection coating (ARC) and 21.4% for a double-layer ARC. The loss analysis is based on an extended characterization of the solar cells and of special samples, which allow the separation of the contributions of each region of the solar cell including metallization. Their impact is determined experimentally on the open-circuit voltage, the short-circuit current density, and the fill factor. Based on the measurements, the devices are numerically simulated. The free energy losses are analyzed using the simulation model. Based on the results from the loss analysis, it is found that the integration of a selective emitter structure and the further improvement of the rear surface would allow for efficiencies above 22% in the short term. [ABSTRACT FROM AUTHOR]