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Implementing antireflection (AR) coatings in micromorph tandem solar cells is a challenging process in which not only more sunlight should get conducted into the cells, but also the current matching between subcells should either be maintained or get improved. In this work, the novel double-layered AR coatings were prepared on either one side or two sides of glass superstrates using hybridized hollow silica nanosphere (HSN) sols. As a result of improvement in light distribution via double-layered AR coatings, the current difference between the top and bottom subcells was decreased to be 0.05 mA/cm 2 , much smaller than that of untreated cells, 0.33 mA/cm 2 . Furthermore, the cells grown on the two-sided AR coated superstrates demonstrated the largest increases in current densities of top and bottom subcells, 4.20% and 7.53%, respectively, which were much higher than those of the cells on one-sided AR coated superstrates. The underlying origin was ascribed to the better light trapping induced by multiscale texturing at front boron-doped zinc oxide (BZO) electrodes, which resulted from the conformal growth of BZO on HSNs with unique surface morphologies. The findings provided a practical way to simultaneously realize light distribution and trapping using the two-sided AR coated glass superstrates without any amendment of layers inside micromorph tandem solar cells. [ABSTRACT FROM AUTHOR]

This paper reports a facile method to prepare a textured surface with combined micron- and nano-scale surface features, which is used as master for nano-imprinting process to obtain transparent front electrodes in thin-film silicon tandem cells. The micron- and nano-scale surface features of the master are formed by combination of SiO 2 sphere pre-deposition and ZnO textured growth. The master exhibits an averaged total transmittance value of 89.7% and an averaged haze value of 54.1% for the wavelength from 380 to 1100 nm. Comparing to the flat reference cell, the thin-film Si tandem cell deposited on the superstrate prepared using this master shows substantial decrease in reflectance at long wavelengths and drastic gain in the photocurrent of the bottom cell, the maximum summed current is enhanced by 35.5%, and the convert efficiency is improved from 8% to 10.0 ± 0.3%. [ABSTRACT FROM AUTHOR]

We study amorphous silicon–germanium (a-SiGe:H) as intrinsic absorber material for thin-film silicon-based triple and quadruple junction solar cells. First, we present the development of a-SiGe:H single junction devices, in particular the Ge-content grading in the absorber layer, the influence of the Ge-content on electrical properties and (infra)red-response, and the influence of using different types of p-layers. We subsequently show the incorporation of optimized single-junction devices in triple junction cells and discuss the interplay between Ge-content and intermediate reflector thickness. For triple junction devices with amorphous silicon (a-Si:H) top cells, a-SiGe:H middle cells and microcrystalline silicion (µc-Si:H) bottom cells, we obtained an initial efficiency of 13.6% and an efficiency of 11.3% after light-soaking. We also present a quadruple junction device with an a-Si:H top cell, a low Ge-content a-SiGe:H second cell, and µc-Si:H third and bottom cells. In this device configuration, we obtained an open-circuit voltage as high as 2.57 V. The performance of these cells was limited by not yet optimized current matching, leading nevertheless to an initial efficiency of 10.1%. A brief roadmap towards quadruple-junction devices with stabilized efficiencies of 14% is also outlined. [ABSTRACT FROM AUTHOR]

When it comes to parasitic absorption in thin-film silicon solar cells, most studies focus on one electrode only, most of the time the substrate (in n-i-p configuration) or superstrate (in p-i-n configuration). We investigate here simultaneously the influence of the absorption in both front and back electrodes on the current density of tandem micromorph solar cells in p-i-n configuration. We compare four possible combinations of front and back electrodes with two different doping levels, but identical sheet resistance and identical light-scattering properties. In the infrared part of the spectrum, parasitic absorption in the front or back electrode is shown to have a similar effect on the current generation in the cell, which is confirmed by modeling. By combining highly transparent front and back ZnO electrodes and high-quality silicon layers, a micromorph device with a stabilized efficiency of 11.75% is obtained. [ABSTRACT FROM AUTHOR]

Abstract: In thin-film silicon solar cells textured interfaces are introduced, leading to improved antireflection and light trapping capabilities of the devices. Thin-layers are deposited on surface-textured substrates or superstrates and the texture is translated to internal interfaces. For accurate optical modelling of the thin-film silicon solar cells it is important to define and include the morphology of textured interfaces as realistic as possible. In this paper we present a model of thin-layer growth on textured surfaces which combines two growth principles: conformal and isotropic one. With the model we can predict the morphology of subsequent internal interfaces in thin-film silicon solar cells based on the known morphology of the substrate or superstrate. Calibration of the model for different materials grown under certain conditions is done on various cross-sectional scanning electron microscopy images of realistic devices. Advantages over existing growth modelling approaches are demonstrated—one of them is the ability of the model to predict and omit the textures with high possibility of defective regions formation inside the Si absorber layers. The developed model of layer growth is used in rigorous 3-D optical simulations employing the COMSOL simulator. A sinusoidal texture of the substrate is optimised for the case of a micromorph silicon solar cell. More than a 50 % increase in short-circuit current density of the bottom cell with respect to the flat case is predicted, considering the defect-free absorber layers. The developed approach enables accurate prediction and powerful design of current-matched top and bottom cell. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate tandem amorphous/microcrystalline silicon solar cells with asymmetric intermediate reflectors grown in the n–i–p substrate configuration. We compare different types of substrates with respect to their light-trapping properties as well as their influence on the growth of single-junction microcrystalline cells. Our most promising back reflector combines a textured zinc oxide film grown by low-pressure chemical vapor deposition, a silver film for reflection, and a zinc oxide buffer layer. Grown on this substrate, microcrystalline cells exhibit excellent response in the infrared while keeping high open-circuit voltage and fill factor, leading to efficiencies of up to 10.0%. After optimizing the morphology of the asymmetric intermediate reflector, we achieve an n–i–p micromorph solar cell stabilized efficiency of 11.6%, using 270nm and 1.7μm of silicon for the absorber layer of the amorphous top cell and the microcrystalline bottom cell, respectively. Using this original device architecture, we reach efficiencies close to those of state-of-the-art n–i–p and p–i–n micromorph devices, demonstrating a promising route to deposit high-efficiency thin-film silicon solar cells on opaque substrates. [Copyright &y& Elsevier]

Abstract: The imprinting of random square based pyramidal textures with micrometric scale at the air/glass interface of thin film silicon solar cells is presented as an efficient alternative to anti-reflective coatings to minimize reflection losses at the cell entrance. This novel processing step, which can be applied after cell or module manufacture, is found to simultaneously enhance light in-coupling and light-trapping in amorphous silicon/microcrystalline silicon tandem solar cells. A remarkable total current gain of more than 5% is demonstrated with the imprinting of such structures, resulting in a tandem cell with a high initial efficiency of 13% for a total absorber layer thickness below 1.5μm. [Copyright &y& Elsevier]

Abstract: We investigate the transfer of random nanostructures commonly used in thin film silicon solar cells onto inexpensive substrates, such as glass or flexible polyethylene sheets. Morphological and optical analyses of masters and replicas show the successful transfer of details with sizes much below 1μm. These high-quality replicas are obtained by UV nano-imprinting, avoiding the use of PDMS as an intermediate mold, which has been identified as being responsible for the lack of resolution found in previous works. [ABSTRACT FROM AUTHOR]

In this work, we present the development of passivating contacts based on thin interfacial oxide/doped poly-silicon for two side contacted c-Si solar cells. In the first part, we discuss our layer optimization towards direct metallisation, using firing through of Ag-paste screen printed on a silicon nitride (SiN x :H). By optimising the poly-silicon thickness, we obtain solar cells with open circuit voltage (V OC) up to 700 mV and fill factor (FF) up to 78%. However, such results were obtained by using layers with a thickness of 95 nm, strongly limiting the short circuit current density. To overcome this limitation, we present in the second part an approach for localization of the front side passivating contact by means of deposition through a shadow mask. Finally, in the third part, we demonstrate high-efficiency c-Si solar cells with promising efficiency above 21.7% with a V OC of ∼711 mV, a high FF of 79.7% and a potential for efficiency >22%. • Thin and transparent front side passivating contacts with thicker regions of metallisation. • One single firing step for paste contacting and hydrogenation of front passivating contact. • Low degradation in locally thickened front metallized area with high V OC >710 mV. • Excellent electrical transport with FF >79.5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • H and D quantification is performed in a nanometer scale thin layer. • Background contribution in APT concentration profile is estimated from SIMS data. • A new correlative method has been proposed to quantify H, D using SIMS and APT. Multiscale characterization of the hydrogenation process of silicon solar cell contacts based on c-Si/SiO x /nc-SiC x (p) has been performed by combining dynamic secondary ion mass-spectrometry (D-SIMS), atom probe tomography (APT), and transmission electron microscopy (TEM). These contacts are formed by high-temperature firing, which triggers the crystallization of SiC x , followed by a hydrogenation process to passivate remaining interfacial defects. Due to the difficulty of characterizing hydrogen at the nm-scale, the exact hydrogenation mechanisms have remained elusive. Using a correlative TEM-SIMS-APT analysis, we are able to locate hydrogen trap sites and quantify the hydrogen content. Deuterium (D), a heavier isotope of hydrogen, is used to distinguish hydrogen introduced during hydrogenation from its background signal. D-SIMS is used, due to its high sensitivity, to get an accurate deuterium-to-hydrogen ratio, which is then used to correct deuterium profiles extracted from APT reconstructions. This new methodology to quantify the concentration of trapped hydrogen in nm-scale structures sheds new insights on hydrogen distribution in technologically important photovoltaic materials. [ABSTRACT FROM AUTHOR]

In this contribution, we present an electron selective passivating contact metallised with a low temperature process to target front side applications in crystalline silicon (c-Si) solar cells. In addition to an interfacial silicon oxide (SiO x) and an in-situ phosphorous doped micro-crystalline silicon (μc-Si(n)) layer, it comprises an ultra-thin indium tin oxide (ITO) layer of 15 nm for lateral conductivity and a hydrogen rich silicon nitride (SiN x :H) layer which serves as hydrogen (H) reservoir and as anti-reflection coating. We use one single thermal treatment for 30 min at 350 °C to sinter the screen-printed paste, to recover sputtering damage induced during ITO deposition, and to diffuse hydrogen from the SiN x :H layer towards the c-Si/SiO x interface where it passivates interfacial defects. Applied to symmetrically processed textured samples, we find implied open-circuit voltage (iV OC) > 728 mV for optimal ITO thickness of 15 nm and annealing temperatures of 350 °C. The developed stack was applied on the front textured side of co-annealed (800 °C) p-type c-Si solar cells in combination with a tunnel oxide hole selective passivating contact on the rear side. We demonstrate solar cells with fill factor (FF) up to 81.9% and an open-circuit voltage (V OC) up to 719 mV. With a short-circuit current density (J SC) of 38.6 mA/cm2, we obtain a final cell efficiency to 22.8%. We find that the annealing of the SiN x :H/ITO stack strongly increases the ITO free carrier density penalizing the solar cell spectral response at high wavelengths. • Full-area highly transparent passivating front contact for p-type solar cells. • Ultra-thin ITO layer of 15 nm yields excellent current extraction with FF of almost 82%. • One single annealing step for hydrogenation and curing of sputtering damage. • SiN x :H no longer sacrificial layer but part of the ARC. [ABSTRACT FROM AUTHOR]

Passivating contacts are key enablers for high efficiency c-Si solar cells. Here, we present our latest advancement in terms of implementation and understanding in fired passivating contacts (FPC) used as rear p + passivating contact in p-type solar cells. We study three different layer configurations and show that the microstructural layer properties play a major role on the surface passivation and charge carrier transport. Upon optimization we demonstrate implied open circuit voltage of 722 mV corresponding to saturation current density of ~7 fA/cm2 and contact resistances below 10 mΩ cm2, when metallized with ITO/Ag. P-type c-Si solar cells employing a screen-printed P-diffused emitter co-fired with the FPC on the rear side with conversion efficiency up to 22.5% are demonstrated. Temperature-dependent measurements on test structures and solar cells reveal that tunneling is the main transport mechanism for FPC layers that crystallize during the firing process, whereas for more amorphous FPC layers, an additional component due to thermionic emission is also present. Finally, we present the efficiency potential of solar cells employing the developed FPC layer as hole selective rear side passivating contact. Image 1 • Latest advances on the understanding and integration of fired passivating contact (FPC) as hole selective contact. • Dependence of the passivation and contact resistance of the FPC as a function of the microstructural layer properties. • Temperature-dependent IV measurements suggests that tunneling dominates holes extraction for highly-crystalline FPCs. • P-type c-Si solar cells employing with a P-diffused emitter and the rear FPC with conversion efficiency up to 22.5%. • Efficiency potential of FPC in p-type c-Si solar cells. [ABSTRACT FROM AUTHOR]

High temperature passivating contacts for c-Si based solar cells are intensively studied because of their potential in boosting solar cell efficiency while being compatible with industrial processes at high temperatures. In this work, the hydrogenation mechanism of fired passivating contacts (FPC) based on c-Si/SiO x /nc-SiC x (p) stacks was investigated. More specifically, the correlation between passivation and local re-distribution of hydrogen resulting from the application of different types of interfacial oxides (SiO x) and post-hydrogenation processes was analyzed. To do so, the applied processing sequence was interrupted at different stages in order to characterize the samples. To assess the hydrogen content, deuterium was introduced (alongside/instead of hydrogen) and secondary ion mass spectroscopy (SIMS) was used for depth profiling. Combining these results with lifetime measurements, the key role played by hydrogen in the passivation of defects at the c-Si/SiO x interface is discussed. The SIMS profiles show that hydrogen almost completely effuses out of the SiC x (p) during firing, but can be re-introduced by hydrogenation via forming gas anneal (FGA) or by release from a hydrogen containing layer such as SiN x :H. A pile-up of H at the c-Si/SiO x interface was observed and identified as a key element in the FPC's passivation mechanism. Moreover, the samples hydrogenated with SiN x :H exhibited higher H content compared to those treated by FGA, resulting in higher iV OC values. Further investigations revealed that the doping of the SiC x layer does not affect the amount of interfacial defects passivated by the hydrogenation process presented in this work. Eventually, an effect of the oxide's nature on passivation quality is evidenced. iV OC values of up to 706 mV and 720 mV were reached with FPC test structures using chemical and UV-O 3 tunneling oxides, respectively, and up to 739 mV using a reference passivation sample featuring a ~25 nm thick thermal oxide. In this work, the hydrogenation mechanism of fired passivating contacts (FPC) based on c-Si/SiO x /nc-SiC x (p) stacks was investigated, by correlating the passivation and local re-distribution of hydrogen. Secondary ion mass spectroscopy (SIMS) depth profiling was used to assess the hydrogen (/deuterium) content. The SIMS profiles show that hydrogen almost completely effuses out of the SiC x (p) during firing, but can be re-introduced by hydrogenation via forming gas anneal (FGA) or by release from a hydrogen containing layer such as SiN x :H. A pile-up of H at the c-Si/SiO x interface was observed and identified as a key element in the FPC's passivation mechanism. Moreover, the samples hydrogenated with SiN x :H exhibited higher H content compared to those treated by FGA, resulting in higher iV OC values. Further investigations revealed that the doping of the SiC x layer does not affect the amount of interfacial defects passivated by the hydrogenation process presented in this work. Eventually, an effect of the oxide's nature on passivation quality is evidenced. iV OC values of up to 706 mV and 720 mV were reached with FPC test structures using chemical and UV-O 3 tunneling oxides, respectively, and up to 739 mV using a reference passivation sample featuring a ~25 nm thick thermal oxide. [ABSTRACT FROM AUTHOR]

A highly efficient hole-selective passivating contact remains the crucial step required to increase the efficiency of polysilicon-based Si solar cells. The future development of solar modules depends on a device structure that can complement the electron-selective tunnel oxide passivating contact with an equivalent hole-selective contact. We investigate plasma enhanced chemical vapor deposited (PECVD) SiN x and atomic layer deposited AlO x as alternative nanolayers for the passivation layer in polysilicon tunnel contacts. We have fabricated p + poly-Si contacts with resistivities below 100 mΩ·cm 2 using these alternative metal oxide and nitride nanolayers. Initial passivation tests yielded low levels of passivation; however, a detailed understanding of the nanolayers elucidated the strategies to improve passivation significantly, achieving an implied open-circuit voltage ( iV OC ) of 698 mV and dark saturation current density ( J 0 ) of 34 fA/cm 2 for a p + poly-Si contact using a PECVD SiN x interlayer. These are among the best reported for nitride-based nanolayer tunneling contacts, with research into nitride-based tunneling contacts being still in its infancy., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Full-area passivating contacts based on SiO x /poly-Si stacks are key for the new generation of industrial silicon solar cells substituting the passivated emitter and rear cell (PERC) technology. Demonstrating a potential efficiency increase of 1 to 2% compared to PERC, the utilization of n-type wafers with an n-type contact at the back and a p-type diffused boron emitter has become the industry standard in 2024. In this work, variations of this technology are explored, considering p-type passivating contacts on p-type Si wafers formed via a rapid thermal processing (RTP) step. These contacts could be useful in conjunction with n-type contacts for realizing solar cells with passivating contacts on both sides. Here, a particular focus is set on investigating the influence of the applied thermal treatment on the interfacial silicon oxide (SiO x ) layer. Thin SiO x layers formed via ultraviolet (UV)-O 3 exposure are compared with layers obtained through a plasma treatment with nitrous oxide (N 2 O). This process is performed in the same plasma enhanced chemical vapor deposition (PECVD) chamber used to grow the Si-based passivating layer, resulting in a streamlined process flow. For both oxide types, the influence of the RTP thermal budget on passivation quality and contact resistivity is investigated. Whereas the UV-O 3 oxide shows a pronounced degradation when using high thermal budget annealing ( T > 860 °C), the N 2 O-plasma oxide exhibits instead an excellent passivation quality under these conditions. Simultaneously, the contact resistivity achieved with the N 2 O-plasma oxide layer is comparable to that yielded by UV-O 3 -grown oxides. To unravel the mechanisms behind the improved performance obtained with the N 2 O-plasma oxide at high thermal budget, characterization by high-resolution (scanning) transmission electron microscopy (HR-(S)TEM), X-ray reflectometry (XRR) and X-ray photoelectron spectroscopy (XPS) is conducted on layer stacks featuring both N 2 O and UV-O 3 oxides after RTP. A breakup of the UV-O 3 oxide at high thermal budget is observed, whereas the N 2 O oxide is found to maintain its structural integrity along the interface. Furthermore, chemical analysis reveals that the N 2 O oxide is richer in oxygen and contains a higher amount of nitrogen compared to the UV-O 3 oxide. These distinguishing characteristics can be directly linked to the enhanced stability exhibited by the N 2 O oxide under higher annealing temperatures and extended dwell times.

The integration of passivating contacts based on a highly doped polycrystalline silicon (poly-Si) layer on top of a thin silicon oxide (SiO x ) layer has been identified as the next step to further increase the conversion efficiency of current mainstream crystalline silicon (c-Si) solar cells. However, the interrelation between the final properties of poly-Si/SiO x contacts and their fabrication process has not yet been fully unraveled, which is mostly due to the challenge of characterizing thin-film stacks with features in the nanometric range. Here, we apply in situ X-ray reflectometry and diffraction to investigate the multiscale (1 Å-100 nm) structural evolution of poly-Si contacts during annealing up to 900 °C. This allows us to quantify the densification and thinning of the poly-Si layer during annealing as well as to monitor the disruption of the thin SiO x layer at high temperature >800 °C. Moreover, results obtained on a broader range of thermal profiles, including firing with dwell times of a few seconds, emphasize the impact of high thermal budgets on poly-Si contacts' final properties and thus the importance of ensuring a good control of such high-temperature processes when fabricating c-Si solar cells integrating such passivating contacts. Overall, this study demonstrates the robustness of combining different X-ray elastic scattering techniques (here XRR and GIXRD), which present the unique advantage of being rapid, nondestructive, and applicable on a large sample area, to unravel the multiscale structural evolution of poly-Si contacts in situ during high-temperature processes.

We investigate hole-selective passivating contacts that consist of an interfacial layer of silicon oxide (SiO x ) and a layer of boron-doped SiC x (p). The fabrication process of these contacts involves an annealing step at temperatures above 750 °C which crystallizes the initially amorphous layer and diffuses dopants across the interfacial oxide into the wafer to facilitate charge transport, but it can also disrupt the SiO x layer necessary for wafer-surface passivation. To investigate the transport mechanism of the charge carriers through the selective contact and its changes during the annealing process, we utilize various characterization methods, such as transmission electron microscopy, micro Raman spectroscopy, and conductive atomic force microscopy. Combining the latter with a sequential removal of material, we assemble a tomographic reconstruction of the crystallized layer that reveals the presence of preferential vertical transport channels.

Despite the progress in the engineering of structures to enhance photocurrent in thin film solar cells, there are few comprehensive studies which provide general and intuitive insight into the problem of light trapping. Also, lack of theoretical propositions which are consistent with fabrication is an issue to be improved. We investigate a real thin film solar cell with almost conformal layers grown on a 1D grating metallic back-reflector both experimentally and theoretically. Photocurrent increase is observed as an outcome of guided mode excitation in both theory and experiment by obtaining the external quantum efficiency of the cell for different angles of incidence and in both polarization directions. Finally, the effect of geometrical parameters on the short circuit current density of the device is investigated by considering different substrate shapes that are compatible with solar cell fabrication. Based on our simulations, among the investigated shapes, triangular gratings with a very sharp slope in one side, so called sawtooth gratings, are the most promising 1D gratings for optimal light trapping.

We present X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD) investigations of CuO thin films electrochemically deposited on an Au(001) single-crystal surface from a solution containing chiral tartaric acid (TA). The presence of enantiopure TA in the deposition process results in a homochiral CuO surface, as revealed by XPD. On the other hand, XPD patterns of films deposited with racemic tartaric acid or the "achiral" meso-tartaric acid are completely symmetric. A detailed analysis of the experimental data using single scattering cluster calculations reveals that the films grown with l(+)-TA exhibit a CuO(1) orientation, whereas growth in the presence of d(-)-TA results in a CuO(11) surface orientation. A simple bulk-truncated model structure with two terminating oxygen layers reproduces the experimental XPD data. Deposition with alternating enantiomers of tartaric acid leads to CuO films of alternating chirality. Enantiospecifity of the chiral CuO surfaces is demonstrated by further deposition of CuO from a solution containing racemic tartaric acid. The pre-deposited homochiral films exhibit selectivity toward the same enantiomeric deposition pathway.