High-efficiency Silicon Solar Cells Research Articles

Characterization and optimization of high-efficiency crystalline silicon solar cells: Impact of recombination in the space charge region and trap-assisted Auger exciton recombination

Characterization and optimization of high-efficiency crystalline silicon solar cells: Impact of recombination in the space charge region and trap-assisted Auger exciton recombination

Nano-size Joule-Heating to Achieve Low-Ohmic Ag-Si Contact on Boron Emitters of n-TOPCon Solar Cells.

Over the past decade, Tunnel Oxide Passivated Contact (TOPCon) solar cells have emerged as a leading technology for high-efficiency silicon solar cells. Conventional metallization processes using silver/aluminum (Ag/Al) pastes encounter significant hurdles due to reliability risks and insufficient contact quality. Recent advancements in laser-induced metallization technologies, particularly laser-enhanced contact optimization (LECO), offer promising solutions. However, the mechanism of silver-silicon (Ag-Si) contact formation on the P+ emitter of TOPCon cells via LECO processing remains incompletely understood. This study designs and prepares two types of glass frits (GF-A and GF-B) for TOPCon cells and investigates the electrical properties of corresponding devices. Advanced techniques are employed to examine the Ag-Siinterfaces. The results demonstrate that GF-A-based TOPCon cells (Cell-A) outperformed GF-B-based cells (Cell-B) due to the construction of a current-confined Ag-Si interface. A composite conductive model for the Ag-Si interfaces by LECO treatment is introduced, revealing the nano-size Joule-heating to achieve the Ag-Si eutectic structure as the underlying formation mechanism. This work contributes to the understanding of metal-silicon contact optimization in solar cells and introduces novel methodologies for laser-induced synthesis and micro-nano interface engineering.

Band Alignment and Surface Photo-Voltage Analysis of C-Si/Siox/Poly-Silicon Passivating-Contact Stacks Through X-Ray Photoelectron Spectroscopy.

Ultrathin SiOx layers and c-Si/SiOx interfaces find application in tunnel-oxide passivated contacts (TOPcon) for high-efficiency silicon solar cells. Here, we investigate their detailed microscopic properties, with specific attention for the case of c-Si(100) substrates, capped either by p-type or n-type poly-silicon layers [c-Si/SiOx/poly-Si (p+) or c-Si/SiOx/poly-Si (n+)]. Our focus is on the effects of the substrate preparation conditions (either by a dry-plasma or wet SiOx process) and the high-temperature annealing step (as required for the poly-Si crystallization) on the SiOx stoichiometry and its microscopic structure. Through advanced photoemission techniques, we find a clearly decreased valence band offset between the c-Si and SiOx (from 4.5 eV to 4.15 eV) when comparing the dry SiOx with the wet SiOx process, independent of the SiOx film thickness, but correlating with the relative fraction of sub-stochiometric Si states. We lastly examine the magnitude of band-bending of the contact structure through controlled in-situ exposure to light of the surfaces and subsequent tracking of core and valence band levels via a surface photovoltage and a junction photo-voltage (JPV) effect. By analyzing this JPV effect qualitatively, we find it to be proportional to the expected quasi fermi level splitting within the c-Si wafer.

Continuous distribution of interface states in n-type double-side poly-Si/SiOx passivating contact solar cells

Advanced passivation contact in high-efficiency silicon solar cells plays an important role for the sake of minimizing recombination losses. A stack of heavily doped polycrystalline silicon (poly-Si) and tunnel SiOx contact has attracted much attention, benefitting from its excellent characteristics of carrier selectivity and passivation, and which has been successfully applied in double-side poly-Si/SiOx passivating contact solar cells. Note that characteristics analysis of defects at tunnel SiOx/c-Si (crystalline silicon) interface remains an issue of concern. Herein, we observe capacitance transient spectroscopy arise from both electron and hole traps in the passivating contact structure of poly-Si(p+)/tunnel SiOx/c-Si(n). Subsequently, we propose a skillful procedure of deep-level transient spectroscopy (DLTS) measurement to confirm that the observed electron and hole traps are located at the tunnel SiOx/c-Si interface but not in the bulk of the c-Si substrate. Finally, we show a clear physical picture of continuous energy distribution for interface states.

Investigation on optical and electrical properties of multilayer ITO/AZO/ITO transparent conductive oxides

This paper examines how varying the thickness of the indium tin oxide (ITO) seed layer, ranging from 8 to 20 nm, impacts the optical, electrical, and structural properties of triple-layer transparent conductive oxide ITO/aluminum doped zinc oxide (AZO)/ITO. ITO and AZO films were deposited by DC and RF magnetron sputtering, respectively. The thickness and density of each layer were measured by X-ray reflectometry (XRR). X-ray diffraction showed that as the thickness of the ITO seed layer increased, both the average size of the crystallites and the volume of the crystalline phase in the AZO film also increased. Measurements of the electrical characteristics indicated a decrease in resistivity as the thickness of the ITO seed layer increased. This reduction is attributed to enhanced charge mobility, resulting from improved crystallinity. It has been shown that a 20-nm-thick ITO seed layer is sufficient to achieve a charge mobility comparable to that of pure ITO films. The photoluminescence spectra have shown a decrease in the concentration of the oxygen vacancies with the introduction of both the cover and seed layers of ITO. The figure of merits (FOM) of the triple-layer coatings and the optical constants of the AZO and ITO films were calculated. The results of this paper indicate that the ITO20/AZO48/ITO12 triple-layer coating possesses optimal characteristics for use in high-efficiency silicon solar cells.

Inkjet-printed boron-doped poly-Si/SiOx passivating contacts

In this study, we explore the utilization of inkjet printing technology with liquid ink to fabricate boron-doped polycrystalline silicon (poly-Si)/SiOx passivating contacts. The impacts of substrate morphology, baseplate temperature, and surface oxide on the printing performance were investigated to achieve distinct printed patterns. Moreover, a pre-oxidation process at 750 °C for 30 min was conducted as a strategy to prevent dopant spreading from the printed pattern via the gas phase during the high-temperature annealing. Thereafter, the influences of annealing temperature on the formed poly-Si passivating contact quality were studied. By applying optimized process conditions on intrinsic poly-Si(i-poly-Si)/SiOx/p-type crystalline Si (c-Si) substrates, promising surface passivation was achieved with an implied open-circuit voltage (iVoc) of 718 mV and a low contact resistivity (ρc) of 6.1 mΩ cm2 after annealing at 950 °C followed by a hydrogenation treatment. Optical images demonstrate that single-droplet dopant lines with a width of 69 μm could be realized on a mechanically polished substrate by printing with a drop spacing of 40 μm, while the line width expands on rough surfaces or when printing with a reduced drop spacing. Furthermore, high-resolution micro-photoluminescence maps clearly illustrate the localization of the boron-doped regions on polished and planar substrates after annealing. We also realized the formation of localized inkjet-printed phosphorus- and boron-doped poly-Si passivating contacts simultaneously within a single annealing step at 950 °C. These findings underscore the potential of inkjet printing as a promising technique for fabricating localized poly-Si/SiOx passivating contacts in high-efficiency silicon solar cells.

Ultrafast laser-annealing of hydrogenated amorphous silicon in tunnel oxide passivated contacts for high-efficiency n-type silicon solar cells

The tunnel oxide passivated contact (TOPCon) concept has been the brightest star in the field of emerging passivating contact techniques for the last few years. It has shown great potential in industrial applications due to the overwhelming advantages of high device efficiency and low cost. Here, we introduce a novel crystallization method using ultrafast laser-annealing by scanning a laser spot onto the surface of hydrogenated amorphous silicon film in TOPCon solar cells. By circumventing the high-temperature environment of the conventional annealing process, it can prevent a large number of dopant atoms from penetrating inside the crystalline silicon (c-Si) substrate, reducing the Auger recombination. Moreover, we can conduct extensive experiments to clarify the optimal conditions, including laser-annealing modes and process parameters. The hydrogenation experiments reveal that direct appropriation of the traditional hydrogenation method is not applicable. An additional ‘dehydrogenation’ step proves necessary, indicating that the differences in hydrogen content within the films due to the divergence between the principles of laser-annealing and high-temperature annealing are probably responsible for this. Consequently, the proof-of-concept devices using laser-annealing technology realize a champion efficiency of 19.91%,highlighting an alternative technical route with substantial potential to achieve high-efficiency crystalline silicon solar cells.

Science in 2025-2027 and the SPQEO journal

Relevance of recent research is important for scientists and journals reporting research results. There are many sources of prognoses and one of them is the Report of European Commission "Looking into the R&I future priorities 2025-2027". It predicts the importance of the following areas for users: healthcare, energy, climate, sustainability and digitalization. The Ukrainian journal Semiconductor Physics, Quantum Electronics and Optoelectronics (SPQEO) actually focuses on these areas and contributes to the development of related knowledge. Monitoring of last SPQEO issues shows some interesting results: (i) the effect of local field amplification, which causes emergence of ponder motive forces acting on viruses until destruction of viral envelopes; (ii) the methods of malignant tumors treatment taking into account their genesis mechanisms and focusing on correction of definite pathogenesis components, while being nontoxic for other organs and tissues; and (iii) manipulation of the spectral characteristics of a “polycarbonate matrix – gold nanostructures – HTTH dye” system due to influence of gold nanostructures. SPQEO paid attention to the improvement of solar cells (SCs) by considering physical effects such as the effect of space charge region (SCR) recombination on the key characteristics of high-efficiency silicon solar cells, such as photovoltaic conversion efficiency and open-circuit voltage, is not only dependent on the charge-carrier lifetime in the SCR, but also on the ratio of hole-to-electron-capture cross section, σp/σn. Non- traditional SCs were also considered: SCs with perovskite thin films, SCs comprising CdS/CIGS heterojunctions, and vitamin B12-patterned silicon hybrids based SCs. Moreover, SPQEO also covers research results in the fields of quantum devices, diamond- like and oxide films, and light-emitting diodes.

Modelling and analysis of high efficiency silicon solar cell using double layers anti-reflection coatings (ARC)

The modernization that is currently taking over across the world is resulting in numerous advancements in a variety of industries, and the most notable and apparent development is the rising use of solar energy, which has become more prevalent every day. Most companies, residences, schools, and other organizations rely mostly on solar energy as the main source of electricity. It was discovered that anti-reflective coating (ARC) had been applied to solar cells with the goal of increasing power conversion efficiency, decreasing reflection loss, and improving absorption. Although a single layer of ARC is sufficient, applying an additional layer might improve the solar cell application’s effectiveness. Hence, the modeling and analysis of double layers of anti-reflection coating (ARC) with different types of materials have been investigated and evaluated using personal computer one-dimensional (PC1D) simulation software. In this study, the double-layer anti-reflection coating on the solar cell was modeled using PC1D, where this software allowed for one-dimensional simulation of the parameters required for the operation of semiconductor-based solar energy systems. The PC1D simulation reveals that SiO2/TiO2 has the highest efficiency (22.82%) and lowest reflection compared to Si3N4/TiO2 and ZnO/TiO2. Also, SiO2/TiO2 generates the highest external quantum efficiency (EQE) among ARC double layers, making it ideal for silicon solar cell applications in order to boost the solar cell’s efficiency. The results for the effects of current, voltage, reflection, and EQE of the different double layers of ARC have also been studied in this paper.

High-efficiency silicon solar cells designed on experimentally achieved nano-engineered low-reflective silicon surface

High-efficiency silicon solar cells designed on experimentally achieved nano-engineered low-reflective silicon surface

Physics of High Efficiency Silicon Solar Cell with Nanoinclusions of Lead Chalcogenides

Physics of High Efficiency Silicon Solar Cell with Nanoinclusions of Lead Chalcogenides

Qualification of laser-weld interconnection of aluminum foil to back-contact silicon solar cells

Laser welding can be used to interconnect high-efficiency back-contact silicon solar cells with low-cost Al foil. This interconnection approach is relatively new and, thus, requires detailed vetting of its reliability before being adopted commercially. In this study, we weld 50-μm-thick Al foil to Sunpower back-contact cells and observe that the laser-weld adhesion, module fill factor, and reliability through thermocycling are all highly correlated to each other. A JMP statistical model built from adhesion data reveals that the statistically significant parameters to improve laser-weld adhesion are the laser pulse energy, pulse density, and pattern. Increasing the laser pulse energy and density improves the foil adhesion to the cell metallization, which is likely because of the improved melting of the Sn capping layer on the Cu electrode of the cells, as identified by cross-sectional microscopy. 94.4% of the modules fabricated using laser welds with a mean adhesion above 0.8 mJ lost less than 5% of their initial maximum power after 200 thermocycles, which is the IEC 61215 criterion for any single accelerated stress test. Additionally, 90.0% of modules fabricated with an as-fabricated module series resistance below 1.9 Ω cm passed thermocycling. Thus, laser-weld adhesion and the as-fabricated module series resistance can be used in the further development of new laser-weld settings and as quality control parameters in the manufacturing of these modules.

Diameter and gap controlled fabrication of periodic SiMW/SiNW arrays: A broadband absorber for high efficiency silicon solar cell

Vertically aligned and periodic silicon micro/nano-wire (SiMW/SiNW) arrays of different diameters were synthesized by combining lithography-free silica particle patterning, reactive ion etching (RIE), and modified metal-assisted chemical etching (MACE) methods. All required silica particles were synthesized, and process parameters were optimized to fabricate sub 50 nm SiNW to large size SiMW with the controlled inter-wire gap. Fabricated SiMW/SiNW array samples show a significant reduction of reflectance (7–9 %) in the silicon absorption band (300 nm–1000 nm). Additional absorption of 25–33 % compared to the planar silicon is observed in the sub-bandgap region of silicon (1100–2000 nm) for these samples, which signifies the effect of field confinement within these structures. The estimated short circuit current density (JSC) using the experimental absorption spectrum of SiMW is 49.96 mA/cm2, which is 16 % higher than the Lambertian limit of ∼43 mA/cm2. This result can lead to the theoretical efficiency of the solar cell up to 28.73 % without the inclusion of the surface passivation effect.

Dramatic Reduction of Silicon Surface Recombination by ALD TiOx Capping Layer from TiCl4 and H2O: The Role of Chlorine.

Amorphous thin-film TiOx prepared via atomic layer deposition (ALD) has been identified as one of the most promising materials for use in transparent passivating contacts in high-efficiency and low-cost crystalline silicon (c-Si) solar cells. As highlighted in this work, the passivation performance of ALD TiOx layers strongly depends on the metal precursor used, with films prepared using TiCl4 recently showing the best results. However, a full understanding of how such films achieve their high level of surface passivation has not yet been demonstrated. This study provides a clear demonstration that a key part of this passivation mechanism is due to chlorine (Cl) accumulation at the Si surface. This mechanism is demonstrated to be quite general in nature by showing how 2 nm of ALD TiOx (TiCl4 + H2O) can be applied as a capping layer for either ZnO or Al2O3 interlayers to dramatically reduce silicon surface recombination. Cl depth profiles obtained using secondary ion mass spectrometry confirm the presence of Cl extending through the depth of the interlayers with a peak at the silicon interface. Remarkably, this diffusion of Cl is observed following low-temperature (75 °C) deposition of the TiOx capping layer, without any subsequent thermal treatment. Contrary to earlier studies that treated residual Cl in ALD films as a general contamination issue, these findings reveal unequivocally that chlorine plays a crucial role in Si surface passivation and can be classed as an effective passivation element, similar to hydrogen in its ability to passivate Si dangling bonds. The outcomes of this research emphasize the importance of residual chlorine in enhancing the passivation of buried interfaces and provide additional motivation for employing metal chloride precursors for silicon surface passivation applications.

Enhancing poly-Si contact through a highly conductive and ultra-thin TiN layer for high-efficiency passivating contact silicon solar cells

High-performance passivating contacts with excellent electron selective property is a prerequisite for silicon solar cells with high power conversion efficiency. In this work, a highly conductive, ultra-thin electron-selective titanium nitride (TiN) film is prepared by reactive magnetron sputtering for tunnel oxide passivated contact (TOPCon) solar cells. The deposition parameters, crystal structure, and chemical state were systematically investigated. A higher TiN content and stronger TiN (111) diffraction peak resulted in higher conductivity. We demonstrated that the TiN film possessed a conductivity as high as 5000 S/cm and a relatively low work function of 4.26 eV. An ultra-thin TiN film (1–2 nm) was inserted between the n+ poly-Si and rear electrode to reduce the interface contact resistance and interface barrier height and subsequently obtain better electron transport. The cross-sectional morphology and elemental distribution of the n+ poly-Si/TiN/Ag interface were tested using high-resolution transmission electron microscopy. The developed TiN film was a proof of concept, and it demonstrated an impressive cell efficiency of 24.6% (Voc = 707.1 mV, Jsc = 41.62 mA/cm2, FF = 83.7%) on TOPCon solar cells. Our work provides vital insights and a detailed supplement toward the optimization of electron contact for silicon solar cells or perovskite solar cells. The outcomes of the study indicate the potential for use in applications involving high fill factor photovoltaic devices.

Space charge region recombination, non-radiative exciton recombination and the band-narrowing effect in high-efficiency silicon solar cells

An expression for finding the dependence of narrowing the bands in silicon ΔEg on the level of illumination from the intrinsic absorption band (or short-circuit current) has been proposed. This expression is used to find experimental values of ΔEg in high-efficient silicon solar cells. The dependence ΔEg (J) or dependence ΔEg (JI), where JI is the short-circuit current density, has been rebuilt into the ΔEg (ΔnOC) dependence, where ΔnOC is the excitation level in open-circuit conditions. With this aim, the generation-recombination balance equation was solved taking into account six recombination mechanisms in silicon, including Shockley–Reed–Hall recombination, radiative recombination, interband Auger recombination, surface recombination, non-radiative exciton recombination, and recombination in the space charge region. The latter two recombination terms are not taken into account in studies of the key parameters of silicon solar cells and in programs for simulating the characteristics of these solar cells. Therefore, in this work their correct definition was performed, their contribution was compared with the contribution of other recombination mechanisms, and it has been shown that the description of the characteristics and key parameters of silicon SC without taking them into account is insufficiently correct. The experimental dependences ΔEg (ΔnOC) obtained in the work were compared with Schenk’s theory. It has been shown that there is a good agreement between them.

Solution-processed vanadium oxide by low-temperature annealing for silicon solar cells with hole selective contact

Transition metal oxides (TMOs) with high work function (V2O5, MoO3, WO3) are very promising hole selective materials for high-efficiency crystalline silicon solar cells, as they can provide excellent hole transport and electron blocking capabilities simultaneously. However, the TMOs are typically obtained using vacuum deposition techniques (thermal evaporation, atomic layer deposition or sputtering), for which the preparation process is complex and the requirement for the equipments is relatively high. In this work, we prepared vanadium oxide (V2O5-X) films using low-cost solution method as the hole-selective transport layer for silicon heterojunction solar cells. The low temperature post-annealing treatment at 150 °C reduces the surface roughness of film and improves the passivation contact performance with p-Si. Furthermore, annealing in an oxygen-deficient atmosphere (N2/H2 = 95/5) improves the carrier transport due to increased oxygen vacancies and enhances the surface passivation ascribed to the additional role of hydrogen. Combined with the annealing treatments and optimized device processes, the V2O5-X/p-Si heterojunction solar cells have achieved a conversion efficiency of 17.23%, which is the highest reported so far based on solution-processed V2O5-X for crystalline silicon solar cells.

Flexible solar cells based on foldable silicon wafers with blunted edges

Flexible solar cells have a lot of market potential for application in photovoltaics integrated into buildings and wearable electronics because they are lightweight, shockproof and self-powered. Silicon solar cells have been successfully used in large power plants. However, despite the efforts made for more than 50 years, there has been no notable progress in the development of flexible silicon solar cells because of their rigidity1–4. Here we provide a strategy for fabricating large-scale, foldable silicon wafers and manufacturing flexible solar cells. A textured crystalline silicon wafer always starts to crack at the sharp channels between surface pyramids in the marginal region of the wafer. This fact enabled us to improve the flexibility of silicon wafers by blunting the pyramidal structure in the marginal regions. This edge-blunting technique enables commercial production of large-scale (>240 cm2), high-efficiency (>24%) silicon solar cells that can be rolled similarly to a sheet of paper. The cells retain 100% of their power conversion efficiency after 1,000 side-to-side bending cycles. After being assembled into large (>10,000 cm2) flexible modules, these cells retain 99.62% of their power after thermal cycling between −70 °C and 85 °C for 120 h. Furthermore, they retain 96.03% of their power after 20 min of exposure to air flow when attached to a soft gasbag, which models wind blowing during a violent storm.

Multi-scale optical simulation of crystalline silicon solar cells by combining ray and wave optics.

Optical simulations allow the evaluation of the absorption, reflection, and transmission of each functional layer of solar cells and, therefore, are of great importance for the design of high-efficiency crystalline silicon (c-Si) solar cells. Here, a multi-scale simulation method (MSM) based on ray and wave optics is proposed to investigate the optical characteristics of c-Si solar cells. The ray and wave optical methods are first independently employed on inverted pyramid glass sheets, where the latter one can describe the size-dependent interfacial scattering characteristics more accurately. Then the optical properties of a c-Si solar cell with a tunnel oxide passivated carrier-selective contact configuration are studied by employing the MSM, where scattering at the interfaces is acquired by a finite-difference time-domain method (wave optics). Since the MSM can accurately simulate optical modes such as the Rayleigh anomaly, Bloch mode, and Mie resonances, the reflection and transmission spectra of the whole device are in good agreement with the measured data. The proposed MSM has proven to be accurate for structures with functional thin films, which can be extended to hybrid tandem devices with top-level cells consisting of stacks of layers with similar dimensions.

Characterization of tunnel oxide passivated contact fabricated by sputtering and ion implantation technique

Tunnel oxide passivated contact (TOPCon) structures using highly doped n-type polycrystalline silicon were fabricated using facing target sputtering and ion implantation techniques for a SiH4-free fabrication process of high-efficiency silicon solar cells. We investigated the structural and electrical properties of the highly doped n-type poly-Si layers to optimize the ion implantation process. We also investigated the surface passivation quality of our TOPCon structure. An effective carrier lifetime of 2.01 ms and an implied open circuit voltage of 704 mV were obtained for our sample annealed at 950 °C. The sample also exhibits a low contact resistance of 3.22 × 10−3 Ω cm−2. Our results open the way for SiH4-free fabrication of silicon solar cells with a TOPCon structure.