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A highly transparent passivating contact (TPC) used for high‐efficiency crystalline silicon (c‐Si) solar cells should meet several key criteria: high optical transparency, excellent c‐Si surface passivation, low contact resistivity, and a low‐temperature fabrication process suitable for device integration. Here, a simple TPC is developed structure consisting of a silicon oxide (SiOx) tunneling passivating layer and an aluminum doped zinc oxide (AZO) electron‐selective transporting layer (SiOx/AZO). This TPC demonstrated remarkable passivation quality with a low contact recombination current density of below 2.2 fA cm−2, an implied open‐circuit voltage of close to 740 mV and a contact resistivity below 20 mΩ·cm2 when contact with lightly doped n‐type c‐Si. This excellent passivation performance can be attributed to improved interfacial hydrogen chemical passivation and the field‐effect passivation induced by the highly Al‐doped ZnO film. Demonstrated n‐type c‐Si solar cells using full‐area SiOx/AZO rear contacts achieved a significant efficiency of 23.17%. Further power loss analysis based on numerical simulations outlines the pathway to achieving efficiencies exceeding 26%. [ABSTRACT FROM AUTHOR]

Solar photovoltaics (PV) are poised to be crucial in limiting global warming by replacing traditional fossil fuel generation. Within the PV community, crystalline silicon (c‐Si) solar cells currently dominate, having made significant efficiency breakthroughs in recent years. These advancements are primarily due to innovations in solar cell technology, particularly in developing passivating contact schemes. As such, this review article comprehensively examines the evolution of high‐efficiency c‐Si solar cells, adopting a historical perspective to investigate the advancements in passivation contact techniques and materials to state‐of‐the‐art cell designs. Additionally, this work deeply studies the recent advances and critical design principles underlying each developed passivation scheme. Eventually, this work identifies existing challenges and proposes insights into future directions for c‐Si solar cells through diverse passivating contact strategies. [ABSTRACT FROM AUTHOR]

The application of molybdenum oxide (MoOx) as a hole-selective contact for silicon-based solar cells has been explored due to superior optical transmittance and potentially leaner manufacturing compared to fully amorphous silicon-based heterojunction (SHJ) devices. However, the development of MoOx contacts has been hampered by their poor thermal stability, resulting in a carrier selectivity loss and an S-shaped IV curve. The aim of this study is to understand the influence of different passivating interlayers on the carrier selectivity of hole-selective MoOx contacts for crystalline silicon (c-Si) solar cells. We highlight the effect of different interlayers on the surface passivation quality, contact selectivity, and the thermal stability of our MoOx-contacted devices. The interlayers studied are intrinsic hydrogenated amorphous silicon (a-Si:H(i)), thermally grown ultrathin SiO2, and a stack consisting of an ultrathin SiOy and Al2O3 layer. Additionally, we simulate the interacting interlayer properties on the carrier selectivity of our MoOx contacts using a simplified model. Among these interlayers, the Al2O3/SiOy stack shows to be a promising alternative to SiO2 by enabling efficient transport of holes while being able to sustain an annealing temperature of at least 250 °C underlining its potential in module manufacturing and outdoor operation.

This work reports the successful synthesis of an efficient near infra-red (NIR) emitting KSrVO 4 :Yb3+ phosphor using the combustion method. The X-ray diffraction technique (XRD) confirmed the orthorhombic phase of a material whereas X-ray photoelectron spectroscopy (XPS) analyzed the elemental makeup and chemical states of the phosphor components. Photoluminescence (PL) analysis revealed that the phosphor exhibit superior thermal stability and emit in the NIR region when activated by near-UV light. An upsurge in emission intensity occurs upon the incorporation of Bi3+ as a co-dopant. Using diffuse reflectance spectra (DRS), optical band gap, metallization constant, and refractive index were computed for all ion concentrations in KSr (1- x) VO 4 : x Yb3+ (0 ≤ x ≤ 0.06). For the optimized concentration of Yb3+ into the host, numerical values of these parameters were also estimated. The studies reveal that the produced material may be applied as a solar spectrum converter to improve the efficiency of crystalline silicon (c-Si) solar cells. [ABSTRACT FROM AUTHOR]

Abstract The evolution of the contact scheme has driven the technology revolution of crystalline silicon (c‐Si) solar cells. The state‐of‐the‐art high‐efficiency c‐Si solar cells such as silicon heterojunction (SHJ) and tunnel oxide passivated contact (TOPCon) solar cells are featured with passivating contacts based on doped Si thin films, which induce parasitic optical absorption loss and require capital‐intensive deposition processes involving flammable and toxic gasses. A promising solution to tackle this problem is to employ dopant‐free passivating contact, involving the use of transparent and cost‐effective wide band gap materials. In this review, we first introduce the dopant‐free passivating contact, from carrier transport mechanisms, material classification to evaluation methods. Then we focus on the advances in different strategies to improve cell performance, including material property optimization, structural and interfacial engineering, as well as various post‐treatments. At the end, the challenge and perspective of dopant‐free passivating contact c‐Si solar cells are discussed.

• Preparation of a multifunctional fluorescent glass that combines light conversion and temperature sensing characteristics. • This glass could strongly absorb ultraviolet light and convert it into visible infrared light to improve the efficiency of c-Si solar cells. • In addition, this type of glass also has dual mode temperature sensing characteristics based on the fluorescence lifetime (FL) and fluorescence intensity ratio (FIR) modes. Borate glasses doped with Ag clusters and Yb3+ were prepared using the conventional melt-quenching method. Fluorescence spectra and decay curve measurements confirmed that energy transfer (ET) occurred from the Ag clusters to Yb3+. The fluorescent glasses can convert ultraviolet light to visible-infrared region which matches well with the spectral response of c-Si solar cells to improve the conversion efficiency. The lifetimes of Ag clusters decreased in Ag clusters mono-doped and Ag clusters/Yb3+ co-doped glasses as the temperature increased. Sensitivity values based on the fluorescence lifetime (FL) were calculated. Furthermore, a high optical sensitivity based on the fluorescence intensity ratio (FIR) technology and the maximum absolute sensitivity (S a) and relative sensitivity (S r) were 4.79 % K −1 and 0.97 % K −1, respectively. Temperature cycling tests demonstrated the repeatability of the luminescence. These results indicate that this fluorescent glass can serve as an excellent temperature sensing material. [ABSTRACT FROM AUTHOR]

Building Integrated Photovoltaic systems can produce a significant portion of the energy demand of urban areas. Despite their potential, they remain a niche technology that architects and project engineers still find esthetically limited. The dark blue or black color of standard photovoltaic panels is considered inappropriate for restoration projects of historic buildings and represents a major constraint on the development of new projects. This work will provide insight into how the use of optic filters can offer new pathways for architectural acceptance of photovoltaic panels. Optic filters selectively reflect or transmit light by interference and can be designed and fabricated using cost‐effective and industrially compatible processes. By using in‐house developed ray tracing software coupled with TCAD Sentaurus, more than 400 colors were obtained, and their impact on the opto‐electrical performance of interdigitated back‐contacted solar cells was studied. Results show a maximum efficiency loss of 1.6% absolute at the perpendicular incidence of light on the range of obtained colors when compared with a standard dark blue solar cell. Simulations for different angles of incidence showed that the current reduction on the standard device could be modeled using a cosine relationship. The colored cells, however, deviated significantly from this relationship. We propose that the angular behavior of any cell (colored or standard) could be simulated by modifying the effective irradiance with scaling factors equal to the ratios of the photogenerated current at any angle with respect to the value at normal incidence. We demonstrate that this approach accurately models the effect of the color filter and allows for an easy transition from a bare cell to an encapsulated one. Due to the spectral effect of the filter, we developed both a spectrally resolved optical model and a two‐dimensional finite volume transient thermal model. In case of the optical model, we demonstrate an accuracy in the prediction of the reflectance produced by the color with values of mean bias error (MBE) between 2.0% and 3.9%. As for the thermal model, it was validated by first analyzing a standard model under conditions of nominal operating cell temperature and then comparing its results with published scientific literature. Later, we compare its prediction against 2 weeks of measurements. In both cases the thermal model proves an adequate accuracy, yielding differences below 1.5°C with respect to other scientific works and an MBE value of 0.89°C as well as a root‐mean‐square error value of 2.10°C for the entire measurement period. With the validated models, we studied the effect of the encapsulation on the color perception. We present two options of color filters. The first one produces relatively low reflectance losses and presents relative annual direct current (DC) energy losses of up to 6.4% for Delft, in the Netherlands, and up to 5.9% for Alice Springs in Australia. However, this first option has very poor color brightness. The second studied filter produces highly saturated bright colors. Improving brightness can increase the annual DC relative losses up to 13.7% and 13.5% for Delft and Alice Springs, respectively. Overall, we demonstrate that colored filters based on multilayer optical stacks are a versatile option for coloring cells that allow a good compromise between esthetics and performance. [ABSTRACT FROM AUTHOR]

Crystalline silicon solar cells with passivating contacts based on doped poly‐Si exhibit high optical parasitic losses. Aiming at minimizing these losses, we developed the oxygen‐alloyed poly‐Si (poly‐SiOx) as suitable material for passivating contacts. From passivation point of view, poly‐SiOx layers show excellent passivation quality and carrier selectivity for both n‐type (iVOC,flat = 740 mV, contact resistance ρc = 0.7 mΩ/cm2, iVOC,textured = 723 mV) and p‐type (iVOC,flat = 709 mV, ρc = 0.5 mΩ/cm2). Optically, due to the incorporation of oxygen, the absorption coefficient of poly‐SiOx becomes much lower than that of doped poly‐Si at long wavelength. Both n‐type and p‐type poly‐SiOx layers are concurrently deployed in front/back‐contacted (FBC) solar cells with a front indium tin oxide (ITO) layer to facilitate the lateral transport of carriers and minimize cell's reflection. A high cell FF of 83.5% obtained in double‐side flat FBC solar cell indicates an efficient carrier collection by these passivating contacts. An active‐area cell efficiency of 21.0% featuring JSC,EQE = 39.7 mA/cm2 is obtained in front‐side textured poly‐SiOx FBC cell, with the potential of further improvement in both VOC and FF. The optical advantage of poly‐SiOx over poly‐Si as passivating contact is also observed with a 19.7% interdigitated back‐contacted (IBC) solar cell endowed with poly‐SiOx emitter and back surface field. Compared to the reference 23.0% IBC solar cell with poly‐Si passivating contacts, the one based on poly‐SiOx passivating contacts shows higher IQE at wavelengths above 1100 nm. This indicates that for both FBC and IBC cells, poly‐SiOx passivating contacts hold potential in enhancing the cell JSC by maximizing the cell spectral response. [ABSTRACT FROM AUTHOR]

This work demonstrates that the application of plated Ni/Cu/Ag contacts for TOPCon solar cells and modules is a reliable alternative to screen-printed metallization. Key advantages of plated metallization is a significant reduction of material costs [B. Grübel et al., in Proceedings 11th SiliconPV Conference, Hamelin, 2021, to be published] due to the substitution of a fully printed silver finger by a stack of a thin nickel seed layer (0.5-1 mm height), highly conductive copper finger (3-10 mm height) and an ultra-thin surface finish by tin (1-3mmheight) or silver (<0.5 mmheight). In this study it will be shown that conventional soldering technology can be used to interconnect plated TOPCon solar cells. We manufactured a 60-cell module using industrial processes. The right choice of plating electrolyte allows low stress and ductile metal finger leading to similar reliability in cell breakage experiments compared to state-of-the-art screen-printing metallization. [ABSTRACT FROM AUTHOR]

Dopant‐free carrier‐selective contacts have attracted considerable research interests, extensively due to the avoidance of high‐temperature doping and their simple, environmental‐friendly fabrication processes for crystalline silicon (c‐Si) solar cells. Herein, a novel dopant‐free electron‐selective material, europium fluoride (EuFx) is developed. A desired Ohmic contact can be formed between lightly doped n‐type c‐Si and aluminum (Al) by inserting nanoscale EuFx films (2–4 nm) through thermal evaporation so as to avoid the high‐temperature phosphorus diffusion and offer a simple, robust process. The contact resistivity is lower than 20 mΩ cm2. EuFx film can effectively select electrons and block holes at the contact interface, which is attributed to its low work function and a large valence band offset with respect to n‐type c‐Si. Combined with an ultrathin silicon oxide (SiO2) as a passivation layer, a champion power conversion efficiency 21.6% of n‐type c‐Si solar cells with full‐area SiO2/EuFx is achieved. An average of absolute efficiency is increased by 12% compared with the reference. The results show that EuFx has particularly excellent electron‐selective transport performance. The new possibility of using lanthanide salts as electron‐selective contacts for photovoltaic (PV) devices is set up. [ABSTRACT FROM AUTHOR]

It has been reported that adding Al to Ag metallization paste can reduce the contact resistivity on boron-doped emitters of n-type c-Si solar cells such as Tunnel Oxide Passivated Contact solar cell(TOPCon), because Al can assist forming Ag–Al spikes and dope into the p + emitter. However, Al addition also increases surface recombination and grid line resistivity. Therefore, a comprehensive understanding to the effect of Al on reducing contact resistivity is crucial for optimization of metallization process. In this paper, we investigated the contact characteristics between Ag–Al pastes with p-Si in comparison with those between Ag paste with p-Si. It was revealed that the driving forces for forming electrical contacts between Ag–Al pastes with p-Si is different from those between Ag pastes with p-Si. Moreover, we found that Al will induce the variation of Ag crystal orientation from (111) plane to (200) plane during firing. This induction process is firmly related to the melting amount of Ag during firing, accompanied by the disappearance of Ag 3 Al. Finally, the effect of Al addition on the contact potential reduction of metal electrodes/p-Si was studied so as to figure out the solution to improving contact properties, which is of great significance for the development of advanced Ag–Al pastes. • The driving forces for forming electrical contacts of Ag–Al pastes is different from Ag pastes. • Al will induce the variation of Ag crystal orientation from (111) plane to (200) plane. • The induction process is related to the melting Ag amount, accompanied by the disappearance of Ag 3 Al. • The effect of Al addition on the contact potential reduction of metal electrodes/p-Si was studied. [ABSTRACT FROM AUTHOR]

In this study, Silicon Dioxide (SiO2) thin films processed by the spin coating method was studied with prepared solutions. Antireflection coating effect of deposited SiO2 thin films on crystalline silicon substrates was analyzed after optimizing the solution, deposition, and thermal treatment processes. The effect of ethanol dilution of the solution was investigated as well. Spectrophotometer reflectance measurements, Scanning Electron Microscopy (SEM) measurements and Afors-het based simulations were carried out. For the prepared solution based SiO2 thin films, the annealing temperature of 950 °C for 7 min in the air was determined as optimum. The minimum surface reflectance of SiO2 coated silicon surface could be reduced below 10% depending on the applied process. Based on the silicon solar cell device simulations, it was revealed that efficiency of a solar cell could be improved 4.23% more thanks to the antireflection coating effect. [ABSTRACT FROM AUTHOR]

The solar spectral converters mainly involve the energy transfer between two codoped ions. Here, we report a series of Ce3+, Cr3+, Ln3+ (Ln = Yb, Nd, Er) tridoped Gd 3 Sc 2 Ga 3 O 12 (GSGO) phosphors with improved absorption and increasing near infrared (NIR) emission. We observed the multiple energy transfer behaviors of Cr3+→Ln3+, Ce3+→Ln3+, Ce3+→Cr3+, and Ce3+→Cr3+→Ln3+ in GSGO matrix. When Ce3+ is introduced into the GSGO:Cr3+,Ln3+ phosphors, the energy transfer of Ce3+→Cr3+→Ln3+ has been realized by utilizing the energy transfer bridge of the Cr3+ ion. Consequently, GSGO:Ce3+,Cr3+,Ln3+ can absorb almost all ultraviolet and visible (UV–Vis) light and produce strong NIR light thanks to the synergistic effect of Ce3+→Cr3+→Ln3+, improving the photovoltaic conversion efficiency of c-Si solar cells. Our results show that the prepared GSGO:Ce3+,Cr3+,Ln3+ have the potential application in the solar spectral material for c-Si solar cells. Meanwhile, the strategy of multiple energy transfers gives a new way to design the spectral conversion materials with wider absorption for c-Si solar cells. Image 1 [ABSTRACT FROM AUTHOR]

Crystalline silicon (c‐Si) solar cells featuring carrier‐selective passivating contacts have become a prominent path to develop highly efficient photovoltaic devices. Development of electron‐selective materials that can provide excellent surface passivation and low contact resistivity to c‐Si substrates while presenting good environmental stability is crucial for practical implementation. Here, an easy approach is demonstrated to achieve low resistivity Ohmic contacts between slightly doped n‐type c‐Si and aluminum electrodes via simple spin‐coating of metal acetylacetone (MAcac) film on a c‐Si surface. Contact resistivity of 1.3 mΩ cm2 (18.2 mΩ cm2 with an a‐Si:H(i) passivating layer) is realized when a thin calcium acetylacetone (CaAcac) interlayer is introduced between c‐Si and Al. An n‐Type c‐Si solar cell with a full area rear a‐Si:H(i)/CaAcac/Al electron‐selective contact is demonstrated with a power conversion efficiency of 21.6%. This work not only demonstrates an approach to develop highly efficient n‐type c‐Si solar cells with effective electron‐selective passivating contacts, but also contributes toward accomplishing a simplified fabrication process for photovoltaic devices, from vacuum to solution processing. [ABSTRACT FROM AUTHOR]

Crystalline silicon (c‐Si) solar cells with carrier‐selective passivating contacts have been prosperously developed over the past few years, showing fundamental advantages, e.g., simpler configurations and higher potential efficiencies, compared with conventional c‐Si solar cells using highly doped emitters. Herein, solution‐processed cesium halides (CsX, X represents F, Cl, Br, I) are investigated as electron‐selective contacts for c‐Si solar cells, enabling lowest contact resistivity down to about 1 mΩ cm2 for slightly doped n‐type c‐Si/CsF/Al contact. After inserting a thin intrinsic amorphous silicon (a‐Si:H(i)) passivating layer, the contact resistivity can still be kept in a low value, about 10 mΩ cm2. With full area rear‐side a‐Si:H(i)/CsF/Al electron‐selective passivating contacts, record power conversion efficiencies of about 21.8% are finally demonstrated for n‐type c‐Si solar cells, showing a simple approach to realize high‐efficiency c‐Si solar cells. [ABSTRACT FROM AUTHOR]

• Top efficiency of 21.15% is reported on large-area n -PERT bifacial solar cells with front selective emitter and rear poly-Si based passivating contacts. • Laser doping is performed to reduce carrier recombination on front borosilicate glass surface based on conventional B-diffusion p + emitter. • Efficiency of 24.64% is predicted by optimizing not only the rear poly-Si based passivating contacts, but also the front emitter and Si substrate parameters. Bifacial crystalline silicon (c-Si) solar cells have currently attracted much attention due to the front high-efficiency and additional gain of power generation from the back side. Here, we have presented n -type passivated emitter and rear totally-diffused (n -PERT) bifacial c-Si solar cells featuring front selective emitter (SE) and polysilicon (poly-Si) based passivating contacts. The SE formation was scanned with laser doping based on front boron-diffusion p + emitter. The poly-Si based passivating contacts consisting of nano-layer SiO x of ~1.5 nm thickness grown with cost-effective nitric acid oxidation and phosphorus-doped polysilicon exhibited excellent passivation for high open-circuit voltage. We have successfully achieved the large-area (156 × 156 mm2) n -PERT bifacial solar cells yielding top efficiency of 21.15%, together with a promising short-circuit current density of 40.40 mA/cm2. Theoretical calculation has further demonstrated that the optimal thickness of SiO x nano-layer will increase from 1.5 nm to 1.8 nm if the density of interface defect state decreases by one magnitude from 1 × 1010 cm−2/eV, and the cell efficiency can be improved up to 24.64% with open-circuit voltage over 0.720 V by optimizing the parameters of functional materials and interface layers. The present work has indicated that the commercialization of low-cost and high-efficiency n -PERT bifacial c-Si cells is possible due to the processes compatible with existing production lines. [ABSTRACT FROM AUTHOR]

Abstract In recent years, considerable efforts have been devoted to developing novel electron-selective materials for crystalline Si (c-Si) solar cells with the attempts to simplify the fabrication process and improve efficiency. In this study, ZnO:Al (AZO) is co-sputtered with SiO 2 to form AZO:SiO 2 films with different SiO 2 content. These nanometer-scale films, deposited on top of thin intrinsic hydrogenated amorphous silicon films and capped with low-work-function metal (such as Al and Mg), are demonstrated to function effectively as electron-selective contacts in c-Si solar cells. On the one hand, AZO:SiO 2 plays an important role in such electron-selective contact and its thickness is a critical parameter, with a thickness of 2 nm showing the best performance. On the other hand, at the optimal thickness of AZO:SiO 2 , the open circuit voltage (V OC) of the solar cells is found to be relatively insensitive to material properties of AZO:SiO 2. Whereas, regarding the fill factor (FF), AZO without SiO 2 content exhibits to be the optimal choice. By using AZO/Al as electron-selective contact, we successfully realize a 19.5%-efficient solar cell with V OC over 700 mV and FF around 75%, which is the best result among c-Si solar cells using ZnO as electron-selective contact. Also, this work implies that efficient carrier-selective film can be made by magnetron sputtering method. Highlights • Magnetron sputtered ZnO:Al (AZO) can be an efficient electron-selective film. • A 19.5%-efficient c-Si solar cell using AZO/Al as electron-selective contact is shown. • The AZO-layer thickness and capping-metal nature are crucial to device performance. [ABSTRACT FROM AUTHOR]

Abstract In this work, a series of Mn4+, Nd3+ and Yb3+ singly and co-doped Ca 3 La 2 W 2 O 12 (CLWO) phosphors were prepared using a high-temperature solid-state reaction approach. In CLWO:0.016Mn4+, the emission spectrum presents a band around 709 nm attributed to Mn4+2E g →4A 2g transition under 365 nm UV excitation, which partly overlaps the excitation spectrum of Nd3+ singly doped CLWO phosphors. This indicates that a non-radiative resonant energy transfer process from Mn4+ to Nd3+ ions would like to take place in Mn4+, Nd3+ co-doped CLWO phosphors. Although scarce spectral overlap between Mn4+ emission and Yb3+ excitation in respective singly CLWO samples is observed, the energy transfer from Mn4+ to Yb3+ ions can also be deduced based on the analyses of excitation spectra, emission spectra and decay times in Mn4+, Yb3+ co-doped CLWO materials, which is proposed to be a phonon-assisted energy transfer process since the energy difference between Mn4+ lowest excited state 2E g and Yb3+ excited state 2F 5/2 is quite large. Moreover, in Nd3+, Yb3+ co-doped CLWO, the energy transfer phenomenon from Nd3+ to Yb3+ ions can be also observed. Therefore, we introduce Nd3+ ions into Mn4+, Yb3+ co-doped CLWO phosphors to realize the Mn4+→Nd3+→Yb3+ successive energy transfer process. Based on this, the Yb3+ emission intensity is highly enhanced in Mn4+, Nd3+ and Yb3+ tri-doped CLWO relative to Mn4+, Yb3+ co-doped CLWO. As a result, with the assistance of two channels Mn4+→Nd3+→Yb3+ and Mn4+→Yb3+ energy transfer processes, the broadband UV/blue light from sunlight spectrum can be effectively converted into Yb3+ near infrared (NIR), matching with the excellent spectral response of solar cells, which is highly expected to improve the c-Si solar cells spectral conversion efficiency. Graphical abstract The enhancement of energy transfer from Mn4+ to Yb3+ in Ca 3 La 2 W 2 O 12 :Mn4+,Nd3+,Yb3+ phosphors via a Nd3+ bridge role for spectral conversion of c-Si solar cells has been investigated in detail. Image 1 Highlights • A novel kind of spectral conversion materials Ca 3 La 2 W 2 O 12 :Mn4+,Nd3+,Yb3+ have been prepared. • Energy transfer from Mn4+ to Nd3+ and Yb3+ ions have been demonstrated in this system. • A novel successive energy transfer channel of Mn4+→Nd3+→Yb3+ in this system has been found. • The enhancement of energy transfer from Mn4+ to Yb3+ has been realized. [ABSTRACT FROM AUTHOR]

Noise spectroscopy as a highly sensitive method for non-destructive diagnostics of semiconductor devices was applied to solar cells based on crystalline silicon with a view to evaluating the quality and reliability of this solar cell type. The experimental approach was used in a reverse-biased condition where the internal structure of solar cells, as well as pn-junction itself, was electrically stressed and overloaded by a strong electric field. This gave rise to a strong generation of a current noise accompanied by local thermal instabilities, especially in the defect sites. It turned out that local temperature changes could be correlated with generation of flicker noise in a wide frequency range. Furthermore, an electrical breakdown in a nonstable form also occurred in some specific local regions what created micro-plasma noise with a two-level current fluctuation in the form of a Lorentzian-like noise spectrum. The noise research was carried out on both of these phenomena in combination with the spectrally-filtered electroluminescence mapping in the visible/near-infrared spectrum range and the dark lock-in infrared thermography in the far-infrared range. Then the physical origin of the light emission from particular defects was searched by a scanning electron microscope and additionally there was performed an experimental elimination of one specific defect by the focused ion beam milling. [ABSTRACT FROM AUTHOR]

Abstract: Advanced classes of modern application require new generation of versatile solar cells showcasing extreme mechanical resilience, large‐scale, low cost, and excellent power conversion efficiency. Conventional crystalline silicon‐based solar cells offer one of the most highly efficient power sources, but a key challenge remains to attain mechanical resilience while preserving electrical performance. A complementary metal oxide semiconductor‐based integration strategy where corrugation architecture enables ultraflexible and low‐cost solar cell modules from bulk monocrystalline large‐scale (127 × 127 cm2) silicon solar wafers with a 17% power conversion efficiency. This periodic corrugated array benefits from an interchangeable solar cell segmentation scheme which preserves the active silicon thickness of 240 µm and achieves flexibility via interdigitated back contacts. These cells can reversibly withstand high mechanical stress and can be deformed to zigzag and bifacial modules. These corrugation silicon‐based solar cells offer ultraflexibility with high stability over 1000 bending cycles including convex and concave bending to broaden the application spectrum. Finally, the smallest bending radius of curvature lower than 140 µm of the back contacts is shown that carries the solar cells segments. [ABSTRACT FROM AUTHOR]

Simple technique of formation of “black silicon” using wet chemical etching of crystalline Si wafers with SiGe self-assembled islands is proposed. The main idea consists of the utilization of SiGe islands as a mask for wet anisotropic etching of Si in alkali-based solution at the first etching stage and further removal of SiGe residuals by etching in a HF:H 2 O 2 :CH 3 COOH mixture at the second etching stage. Initial samples were the crystalline Si wafers with SiGe islands formed on them by deposition of 2.5–14 nm of Ge at 800 °C. After the two above-mentioned etching steps a submicron relief on a Si surface was formed. Investigation of optical properties of fabricated structures revealed significant decrease of reflection (AM 1.5 G weighted reflection ~2–3%) and increase of absorption in the wavelength range of 500–1200 nm. Due to the very small amount of Si removal (<0.5 µm), utilization of standard chemicals for Si-based solar cell technology and potential suitability for usage in large-scale manufacturing the proposed technique is promising for increasing of efficiency of thin wafers crystalline Si solar cell. [ABSTRACT FROM AUTHOR]

In this work, we report on a novel structure of Interdigitated Back-Contacted (IBC) solar cells on c-Si p-type substrates that combines laser processed homojunction base contacts and silicon heterojunction (SHJ) emitters. These hybrid devices which can lead to potential benefits in device processing and/or conversion efficiency. In the proposed fabrication process special attention has been paid to the compatibility of both involved technologies: silicon heterojunction and laser doping from dielectric films. In particular, we focus on the surface passivation obtained by the heterojunction emitter after removing the aluminum oxide/silicon carbide (Al 2 O 3 /SiC x ) layer stack needed for the laser doping process and previously deposited on the c-Si surface. A severe passivation degradation after plasma etching process to remove the top SiC x film is observed, despite leaving the Al 2 O 3 film on the c-Si surface. Based on high-frequency capacitance-voltage characterization, an increase in the interface state density and a strong impact on the fixed charge density is deduced. Next, in order to choose an optimized metallization technology that could simultaneously contact both the ITO film and the p + laser processed regions, we evaluate the contact quality of Titanium and Aluminum on ITO. Results show that Titanium is a better option with a specific contact resistance of 1.1 mΩ cm 2 . Finally, finished hybrid IBC solar cells with conversion efficiencies in the 18-19% range are reported. [ABSTRACT FROM AUTHOR]

We have presented thin Al2O3 (~4 nm) with SiNx:H capped (~75 nm) films to effectively passivate the boron-doped p+ emitter surfaces of the n-type bifacial c-Si solar cells with BBr3 diffusion emitter and phosphorus ion-implanted back surface field. The thin Al2O3 capped with SiNx:H structure not only possesses the excellent field effect and chemical passivation, but also establishes a simple cell structure fully compatible with the existing production lines and processes for the low-cost n-type bifacial c-Si solar cell industrialization. We have successfully achieved the large area (238.95 cm2) high efficiency of 20.89% (front) and 18.45% (rear) n-type bifacial c-Si solar cells by optimizing the peak sintering temperature and fine finger double printing technology. We have further shown that the conversion efficiency of the n-type bifacial c-Si solar cells can be improved to be over 21.3% by taking a reasonable high emitter sheet resistance. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In order to evaluate module materials, the maximum theoretical value of the photo-generated current density, was calculated. The calculation was performed for four different solar cells, a standard p-type, passivated emitter and rear contact (PERC), bifacial cell and interdigitated back contact (IBC) considering a solar spectrum of Atacama Desert, the transmittance of several glass-encapsulant-glass structures and quantum efficiency. Regarding the solar spectrum in Atacama, an average air mass (AM) at noon for this location averaged 1.17 and the photovoltaic (PV) modules tilt angle was 20°. When studying the impact of using glass and encapsulants combined with a solar cell under the same solar spectrum, ethylene vinyl acetate (EVA) with low ultraviolet (UV) cutoff led to the higher current density values, up to 2% higher with the IBC solar cell compared to the other solar cells. The highest current gain, when studying the impact of the two spectra in the 300–1200 nm wavelength range, was 7.4% for the IBC solar cell, obtained with a standard 3.2 mm glass, a thermoplastic material (TM) as encapsulant. Considering the UV part of the spectrum, the current gain was maximized with a glass with an anti reflection coating (ARC) combined with the TM encapsulant for the IBC solar cell (25%). A quantification of losses due to reflection in the glass and absorption in the encapsulant revealed that the glass with ARC and the TM encapsulant different than EVA led to the lowest reflection and absorption losses. In this case, the reflection and absorption came down to 4.8% and 0.9%, respectively, contrasting with the 7% and 2.8% loss produced with the standard glass and EVA encapsulants. [ABSTRACT FROM AUTHOR]

Boron-oxygen defects can cause serious light-induced degradation (LID) of commercial solar cells based on the boron-doped crystalline silicon (c-Si), which are formed under the injection of excess carriers induced either by illumination or applying forward bias. In this contribution, we have demonstrated that the passivation process of boron-oxygen defects can be induced by applying forward bias for a large quantity of solar cells, which is much more economic than light illumination. We have used this strategy to trigger the passivation process of batches of aluminum back surface field (Al-BSF) solar cells and passivated emitter and rear contact (PERC) solar cells. Both kinds of the treated solar cells show high stability in efficiency and suffer from very little LID under further illumination at room temperature. This technology is of significance for the suppression of LID of c-Si solar cells for the industrial manufacture. [ABSTRACT FROM AUTHOR]

The Tm 3+ 800 nm upconversion emission corresponding to the 3 H 4 → 3 H 6 transition has been obtained upon infrared sub-Si bandgap excitation at 1210 nm in Tm 3+ doped transparent glasses and glass ceramics with composition SiO 2 –Al 2 O 3 –CdF 2 –PbF 2 –YF 3 . Possible energy transfer mechanisms have been carefully studied through different experimental measurements such as the excitation spectrum, decay rate of the emission and laser pump power versus integrated emission. The results suggest that energy transfer upconversion (ETU) mechanism is responsible for the emission. It is based on the following process: Tm 3+ ( 3 F 4 )+Tm 3+ ( 3 F 4 )→Tm 3+ ( 3 H 6 )+Tm 3+ ( 3 H 4 ). The upconverted emission is about three times more intense in the glass ceramic samples than in the precursor glasses. This emission can be used to enhance the performances in crystalline silicon (c-Si) solar cells. [ABSTRACT FROM AUTHOR]

In the last years, there is a clear trend in c-Si solar cell fabrication to place both emitter and base contacts on the back side leading to the so-called Interdigitated Back Contacted (IBC) solar cell structure. This solar cell architecture requires excellent front and rear surface passivation as well as a very low recombination emitter. Moreover, laser doping may be an attractive technique to create both selective emitter and base contacts using appropriate dielectric layers as dopant sources, i.e. Al 2 O 3 and a-SiC x (n) stacks for the p + and n + regions respectively. In this study, we report on a simplified fabrication process for IBC n-type c-Si solar cells combining laser doping and a conventional boron emitter passivated by Al 2 O 3 films. Results show very low emitter recombination currents in the ∼10-50 fA/cm 2 range before laser processing. In addition, selective emitter contacts can be created by laser doping with recombination current densities at each contact point around 4.4 pA/cm 2 in relatively low and shallow doped boron doped profiles (sheet resistance ∼400 Ω/sq). Finally, IBC solar cells, 3 x 3 cm 2 device area, were fabricated combining selective laser-doped emitter and base contacts reaching efficiencies up to 20.8%. [ABSTRACT FROM AUTHOR]

In this work, we report on improving efficiency of DopLa cells fabricated on p-type substrates. This type of solar cells has all the highly-doped regions based on laser doping from dielectric films resulting in a very simple fabrication process. Depending on the dopant type, emitter regions or high/low doping junctions related to base contacts can be created. The emitter regions are located at the rear surface in order to be contacted by a continuous metal film without penalizing in shadowing losses, while the front surface shows a typical finger grid configuration with the base contacts under the metal. In a previous work, the reported efficiency was limited by optical losses at the front planar surface. As a consequence, we focus on the introduction of a texturized front surface to the device. Firstly, we characterize the contact formation by laser processing on texturized surfaces by SEM image showing that the size of the contacted region is difficult to determine. By measuring contact resistance and surface recombination velocity, we deduce that the laser process of such surfaces leads to a contacted region which is smaller than the one where passivation is lost. The obtained information is included in 3D simulations to get the optimum size of the contacts, i.e. optimum laser power. Additionally, a new front grid metallization is introduced in order to reduce shadowing. Due to the rear emitter configuration of these devices, front surface recombination is crucial for collecting photogenerated carriers. Thus, optimum laser power is very close to the minimum to obtain a reliable contact. Finally, 2x2 cm 2 solar cells are fabricated with a best efficiency of 17.0%. [ABSTRACT FROM AUTHOR]

• The effects of TeO 2 on the sintering of c-Si solar cell are systematically studied. • TeO 2 affects the morphology of the grids on the sintering process of Ag pastes. • TeO 2 promotes Ag pastes sintering and improves the conductivity of Ag grids. • TeO 2 promotes the growth of the Ag nanocrystallites in Ag/Si contact interface. • An optimal conversion efficiency of solar cells was acquired at TeO 2 content ∼40%. Glass frits, as a critical ingredient, plays an important role between Ag electrode and crystalline silicon (c-Si) solar cells and determines sintering properties of the silver paste and contact quality with c-Si solar cells. Here glass frits with different contents of TeO 2 are prepared and used to investigate the sintering process and effects of contact quality of Ag pastes on c-Si solar cells. Microstructures and electrical properties of the Ag/Si contact interface and performances of the resultant c-Si solar cells are characterized systematically. The results show that TeO 2 promotes the growth of Ag nanocrystallites in the glass layer between Ag grids and c-Si wafers, thus reduces the contact resistance of the Ag grids and improves the contact quality of the Ag/Si interfaces. Moreover, TeO 2 improves the densification and conductive performances of the Ag grids. However, excessive TeO 2 has a negative effect on the conductivity of the Ag grid due to the increased thickness of the glass layer. Based on the competing factors played by TeO 2 , the conversion efficiency is the highest at an optimized TeO 2 content ∼40%. [ABSTRACT FROM AUTHOR]

One of the most common strategies in high-efficiency crystalline silicon (c-Si) solar cells for the rear surface is the combination of a dielectric passivation with a point-like contact to the base. In such devices, the trade-off between surface passivation and ohmic losses determines the optimum distance between contacts or pitch. Given a certain pitch, the series resistance related to majority carrier flow through the base and the rear point-like contact ( R base ) is commonly calculated a-priori and not crosschecked in finished devices, since typical techniques to measure series resistance lead to an unique value that includes all ohmic losses. In this work, we present a novel method to measure R base using impedance spectroscopy (IS) analysis. The IS data at high frequencies allow to determine R base due to the presence of the capacitor formed by the metal/dielectric/semiconductor structure that covers most of the rear surface. The method is validated by device simulations where the dependence of R base on carrier injection, base resistivity and pitch are reproduced. Finally, R base is measured on finished devices. As a result, a more accurate value of the contacted area is deduced which is a valuable information for further device optimization. [ABSTRACT FROM AUTHOR]

In this work, we describe a novel fabrication process of p-type interdigitated back contact (IBC) silicon solar developed by means of laser doping and laser firing techniques. We use dielectric layers both as dopant sources to create highly-doped regions and as passivating layers. In particular, we use phosphorus-doped silicon carbide stacks (a-SiC x (n)) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and aluminum oxide (Al 2 O 3 ) layer deposited by atomic layer deposition (ALD). Emitters were fabricated with a light thermal phosphorus diffusion in order to reduce bulk and surface emitter recombination losses. Highly doped regions n ++ (emitter) and p ++ (base) were simultaneously created in a point-like structure using a pulsed Nd-YAG 1064 nm laser in the nanosecond regime by laser processing the dielectric layers. The results obtained for a cell, 3x3 cm 2 , are presented. Efficiencies up to 18.1% ( J sc = 39 mA/cm2, V oc = 632 mV, FF = 73.4%) have been achieved in our fabricated IBC cells. [ABSTRACT FROM AUTHOR]

Plated Ni/Cu/Ag contacts are an industrially feasible metallization approach for high efficiency c-Si solar cells with low surface doping concentrations (10 18 cm -3 < N D < 10 20 cm -3 ). The 2d-simulations of this work define the minimum requirements on the contact resistivity of metal contacts in a high efficiency solar cell design. The following experimental study of the contact resistivity of plated Ni/Cu/Ag contacts on lowly doped phosphorus emitter demonstrates low contact resistivities in the mΩcm 2 regime, which enable solar cells with high fill factors. Furthermore, the paper analyzes the influence of the thermal silicidation process on pseudo-fill factor losses and on the mechanical contact adhesion. The contact adhesion is also studied with respect to the laser contact opening process. The results of this work demonstrate that the right choice of back-end processes enable plated Ni/Cu/Ag contacts with low contact resistivities in combination with high contact adhesions above 1 N/mm. [ABSTRACT FROM AUTHOR]

In this work, we report on the fabrication and characterization of n-type c-Si solar cells whose p + emitters are based on laser processed aluminum oxide/silicon carbide (Al 2 O 3 /SiC x ) films. The p + emitter is defined at the rear side of the cell and it consists of point-like laser-diffused p + regions with a surface charge induced emitter in between based on the high negative charge located at the Al 2 O 3 /c-Si interface. These emitters are fabricated at low temperature (< 400 °C) and could be directly compared to silicon heterojunction emitters with the advantage that the deposition of a Transparent Conductive Oxide (TCO) film can be avoided, since they are based on p + /n c-Si homojunctions. Additionally, the involved films are transparent to the IR photons ( >1000 nm) that reach the rear surface of the cell resulting in an excellent back reflector. We fabricated solar cells with distance between p + regions or pitch ranging from 200 to 350 μm with a front surface based on silicon heterojunction technology. Best efficiency (18.1%) is obtained for a pitch of 250 μm as a consequence of the trade-off between V oc and FF values. [ABSTRACT FROM AUTHOR]

In this work, we report on the fabrication and characterization of n-type c-Si solar cells whose p+ emitters are based on laser processed aluminum oxide/silicon carbide (Al2O3/SiCx) films. The p+ emitter is defined at the rear side of the cell and it consists of point-like laser-diffused p+ regions with a surface charge induced emitter in between based on the high negative charge located at the Al2O3/c-Si interface. These emitters are fabricated at low temperature (< 400 °C) and could be directly compared to silicon heterojunction emitters with the advantage that the deposition of a Transparent Conductive Oxide (TCO) film can be avoided, since they are based on p+/n c-Si homojunctions. Additionally, the involved films are transparent to the IR photons (◻ >1000 nm) that reach the rear surface of the cell resulting in an excellent back reflector. We fabricated solar cells with distance between p+ regions or pitch ranging from 200 to 350 μm with a front surface based on silicon heterojunction technology. Best efficiency (18.1 %) is obtained for a pitch of 250 μm as a consequence of the trade-off between Voc and FF values. [ABSTRACT FROM AUTHOR]

Wafer thickness reduction is the main trend for cost reduction of crystalline silicon (c-Si) solar cells. For better light trapping in lower thickness wafers where traditional texturization method may not be promising, alternative techniques are being explored. Here, reflection minimization using silver ultra thin film sandwiched between silicon nitride (SiN) antireflection coating (ARC) layers on c-Si substrate is reported. SiN ARC layers were deposited by plasma-enhanced chemical vapor deposition (PECVD) and silver ultra thin film by e-beam evaporation; 41 % reflection reduction for silver ultra thin film sandwiched in SiN ARC layers as compared to standard 80 nm thin SiN ARC on c-Si substrate is shown. The sandwiched structure gives 8.1 % weighted total reflectance for wavelength range of 300-1,200 nm as compared to standard 80-nm SiN-based ARC which gives 13.8 %. Also, comparison of this Ag ultra thin film-based sandwiched geometry is done with randomly distributed nanoparticle (NP)-based ARC geometry. It is shown that optically, the sandwiched Ag ultra thin film-based device geometry is more promising than Ag NP-based device geometry and standard 80-nm SiN-based geometry for broad wavelength range of 300-1,200 nm. [ABSTRACT FROM AUTHOR]

Seeking efficient light trapping structures with both superior omnidirectional and electrical performance is always on the way for increasing electrical energy output of c -Si solar cell over a wide range of light incident angle (θ). Here, tile angle (δ) of quasi-periodic structure arrays is systematically modulated from 35.9° to 72.8° on diamond-wire-sawn (DWS) c -Si by a simple and cost-effective Cu and Ni co-assisted chemical etching way followed by a post treatment. Interestingly, compared with the conventional micro pyramid (MP), the optimized inverted pyramid (IP) like arrays with a δ of 64° possess both lower light reflectance and carrier recombination, leading to a corresponding solar cell with a higher efficiency (∼19.67%) than that of MP based counterpart (∼19.31%). Moreover, during the increase of θ, the external quantum efficiency (EQE) of 64° IP based cell drops much more slowly than that of MP based one by properly adjusting the relative position of the structure arrays and incident light, indicating its omnidirectional property. Simultaneously, a maximum relative enhancement of electrical output power approaching ∼5.8% in the θ range of −90°–90° is achieved on 64° IP based cell compared to the MP based one, the mechanism behind which is further explained by optical simulation. The above finds pave a new way to increase the electrical energy output in a simple and cost-effective way. • Tilt angle control of quasi-periodic IP was achieved by varying Cu and Ni ratio. • 0.36% absolute increase in solar cell efficiency was made based on 64° IP. • ∼5.8% relative increase of output power was achieved on 64° IP based cell. • Mechanism behind omnidirectional performance was explained by optical simulation. [ABSTRACT FROM AUTHOR]

Abstract: In this work use of Ni/Cu double layers as front contact on commercial c-Si solar cells for low concentration application is proposed. The front contact consists of Ni and Cu layers, which are deposited using electroless deposition and electroplating, respectively. These double layers of metals help in reducing the series resistance of solar cells. Ni is deposited on Si wafers (solar cells processed up to ARC deposition but without front contact), using Ni salt and a reducing agent in an electroless bath. Further the Ni deposited wafers are annealed between temperatures 400 and 430°C, to obtain NiSi (nickel silicide), which lowers the contact resistivity between Ni and Si. Formation of NiSi and reduction in contact resistivity are confirmed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission line model (TLM) analysis. Contact resistivity as low as 9mΩcm2 is achieved for the annealed wafers. The NiSi layer is further electroplated with Cu to reduce metal grid line resistance. A reduction in series resistance of about 50% as compared with commercial Ag screen printed solar cells (series resistance approximately 40mΩ) is achieved for the Ni/Cu plated front contact solar cells (series resistance approximately 20mΩ) of area 4×4cm2. I–V characteristic of these solar cells under 2–4 suns concentration is measured and their performance compared with those of commercial Ag screen printed solar cells. [ABSTRACT FROM AUTHOR]

Abstract: The design of a solar cell should have into consideration a multiplicity of factors, including the incorporation or not of the BSF (back surface field), surface passivation and the contact grids. The cell series resistance plays an important role on efficiency determination. Thus, the cell structure and contact grids should be carefully designed taking into account the mentioned factors. The contacted fraction, defined as metal–semiconductor contacted area divided by total cell area, emerges as a key parameter to be optimized because it affects simultaneously the photogenerated current and the series resistance of the solar cell. Here we present a detailed analysis of the different contributions to the series resistance of a c-Si solar cell considering different scenarios. Using a proposed model to describe the cell behaviour based on a 1-D approach, the contacted fraction of the rear contact was optimized for cells with and without BSF. The results obtained show a larger series resistance for cells without BSF leading to higher values of optimum contacted fraction. The dependence of this optimum on cell thickness and base resistivity was also analyzed. In cells with BSF was found a weak dependence on both parameters, while in cells without BSF this dependence was more pronounced. Finally, the influence of metal–semiconductor contact resistance was considered. A higher limit of 0.01Ωcm2 was found to the metal–semiconductor resistance without affecting seriously the efficiency of the device. [Copyright &y& Elsevier]

An experimental facility was developed to asses in situ the degradation of crystalline silicon solar cells, fabricated by the Solar Energy Group of the National Atomic Energy Commission (CNEA), by measuring the current–voltage characteristic curve. The cells were irradiated with 10 MeV protons and fluences between 108 and 1013 p/cm2, using an external beam of the linear tandem accelerator TANDAR, at CAC-CNEA. Furthermore, theoretical simulations were performed to establish the relation between the variation of the electrical parameters and the degradation of the lifetime of minority carriers in the base. The damage constant for 10 MeV proton irradiated silicon solar cells of n+–p–p+ structure and 1 Ω cm base resistivity was determined. Finally, a proposal of a new model of radiation damage for silicon solar cells is discussed. [Copyright &y& Elsevier]