The market uptake of silicon heterojunction (SHJ) solar modules is projected to increase rapidly, which is expected to play a significant role in future sustainability. However, a major barrier to the mass production of SHJ solar modules is significant power degradation under ultraviolet (UV) irradiation. Here, we reported a 98.13% high-quantum yield and highly reliable CaSrSiO4:Ce3+ UV-to-blue-violet downshifting (UV-DS) inorganic phosphor for photovoltaic applications, which could minimize UV-induced degradation, the levelized cost of energy, and the generation of photovoltaic module waste. The CaSrSiO4:Ce3+ inorganic phosphor was synthesized via a solid-state reaction method, where Ce3+ ions preferentially occupy the 7-coordinated Ca site. As a proof of concept, an outstanding output power of 776.2 W and a module efficiency of 24.99% were achieved on 3.1 m(2) industrial-scale module. Only 2.49% power degradation was observed after 180 kWh/m(2) UV irradiation. A statistical lifetime assessment based on UV irradiance data of Chinese geographical locations proven that UV-DS encapsulants significantly enhanced the long-term stability of modules, with better power generation performance and economic and environmental characteristics. Our study offered a blueprint for designing SHJ photovoltaic modules sustainably and strategically for targeting geographic markets, mitigating one of the environmental risks associated with SHJ modules and accelerating practical application.

The bifaciality of solar cells plays a crucial role in determining their overall energy generation performance, particularly in high-reflectance environments where enhanced rear-side light absorption can significantly boost power output. Compared to silicon heterojunction solar cells, a major barrier to the further increasing market competitiveness of tunnel oxide passivated contact (TOPCon) solar cells is the lower bifaciality. In this work, we reported an excellent 94.3 % bifaciality of TOPCon solar cells by formation of rear-side selective sunken pyramid structure on the non-electrode area. The zebra-crossing passivation contact technology was developed without sacrificing the efficiency, where the passivation layers were designed as SiO2/poly-Si/Al2O3/SiNx under silver electrodes and Al2O3/SiNx on rear-side texture area. The optimised rear-side short-circuit current density increased by 3.26 mA/cm2 compared to the baseline, leading to a notable improvement in rear-side light absorption and current generation. As a proof-of-concept, the bifacial TOPCon photovoltaic modules were encapsulated with an impressive bifaciality of 91.7 % and a power output of 722.0 W. It is the highest bifaciality so far for TOPCon solar cells and modules to the best knowledge. Our study offers a blueprint for designing high bifaciality TOPCon solar cells and modules, making them more efficient and versatile than traditional glass/ backsheet modules and accelerating practical application.

Silicon heterojunction (HJT) photovoltaic module is sensitive to UV irradiation, which makes UV-down shifting films and UV-cutoff films widely used during module encapsulation. However, this method leads to significant variations in Spectral Responsivity (SR) within the UV spectrum band. To evaluate the difference of the two different encapsulants, the modules encapsulated with UV-downshifting and UV-cutoff technologies were prepared from identical cells and subjected to controlled outdoor field testing. A deviation in power output was detected in the UV-downshifting modules. In response, solar simulator filters were modified to generate spectra with varying UV intensities, and the SR of both module types was subsequently analyzed. The spectral mismatch encountered during Standard Test Conditions (STC) power testing was theoretically calculated and experimentally confirmed, showing a maximum deviation of 1.15%. By maintaining consistent encapsulation films for both reference modules and tested modules, spectral mismatch during testing can be effectively mitigated. After correcting the STC power of the UV-downshifting module, a specific yield (SY) gain of 0.51% was achieved for the UV-downshifting module compared to the UV-cutoff module during outdoor testing. This study provides empirical evidence on the performance of UV-downshifting and UV-cutoff modules in outdoor conditions, and addresses spectral mismatch challenges between the STC measurement and outdoor application.

n-Type tunnel oxide passivated contact (TOPCon) solar cells are expected to dominate the global photovoltaic market in the next decade, primarily owing to their rapidly increasing power conversion efficiency (PCE). However, acids generated from encapsulant hydrolysis under damp-heat (DH) conditions significantly impair the reliability of TOPCon solar cells. This study evaluated the degradation behavior of TOPCon solar cells under an accelerated test in an ambient acid environment. Exposure to acetic acid for 48 h resulted in the average peel force decreasing from 3.94 to 2.67 N. The study revealed significant deterioration in the contact between the silver-aluminum electrodes and silicon, as well as between the busbar and ribbon, which can be attributed to the corrosion of surface electrodes and the Pb-Sn-Bi alloy-coated ribbon in acetic acid. This deterioration led to a decrease in the front side PCE of TOPCon solar cells by 4.38% and in the rear side PCE by 2.16%, likely owing to differences in the metal contact composition on each side. As a proof-of-concept, the encapsulant was optimized by changing the additives to neutralize the acid produced during the damp-heat process. Following this modification, the PCE degradation of the glass/backsheet module after 2000 h of damp-heat (DH2000)-accelerated test was reduced from 6.49 to 1.54%. This research highlights the vulnerability of TOPCon solar cells to acetic acid exposure and emphasizes the electrochemical reactivity of metallization as a potential risk to the long-term operation of TOPCon modules. It also proposes potential improvements to the encapsulant, which are crucial for enhancing the performance and ensuring the long-term reliability of TOPCon modules.

Halogen compounds are widely used in many advanced photovoltaic technologies including silicon solar cells, perovskite solar cells, and perovskite/silicon tandem cells. They not only play a key role in passivating inter-material contacts, but also act as an excellent anti-reflective layer. Here we reveal that the halogen compound serves as a double-edged sword for solar cells: on one hand, it maintains an inert surface with good anti-reflectivity and enhances short-circuit current density (J(SC)) by up to 0.46 mA/cm(2), resulting in an enhanced power conversion efficiency (E-ff) of silicon heterojunction (SHJ) solar cells to 25.37%; on the other hand, it significantly deteriorates the optoelectronic properties in subsequent damp-heat (DH) tests. Extensive experimental analyses and first-principles simulations demonstrate that the diffusion of fluoride ions and their subsequent reaction with water under DH conditions is key to such behaviors, producing corrosive substances and creating lattice defects in the microstructure of a-Si:H/c-Si(n). Importantly, we successfully reduce E-ff degradation from >53 rel.% to 0 rel.% by incorporating a precisely engineered low-cost dielectric thin layer to impede fluoride diffusion, leading to a degradation-free high-efficiency fluoride-coated SHJ solar cell. This work provides vital insights for maintaining long-term durability of SHJ and will facilitate wide adoption of high-stability silicon solar cells and perovskite/silicon tandem devices.

Large-seed-induced regulation significantly impacts perovskite film grain growth; however, it inadequately addresses stress and defect issues at the perovskite interface. To counter this, we introduce an innovative self-disintegrating seed approach, employing 2D (4-FBZA)2PbI4 perovskite to enhance the crystallization process. During perovskite crystal growth, (4-FBZA)2PbI4 could disintegrate and release 4-FBZA+ ions. These ions effectively anchor the perovskite interface and interact with FA+ and [PbI6]4- within the lattice, passivating defects and releasing detrimental stress. This strategy results in reduced nonradiative recombination and residual stress, culminating in perovskite solar cells (PSCs) achieving a champion power conversion efficiency (PCE) of 23.73% and a remarkable fill factor of 83.64%. Crucially, unencapsulated PSCs retain over 90% of their initial PCE following 2000 hours of exposure in ambient conditions at 25±5 °C and 60% relative humidity.

The two-step sequential deposition strategy has been widely recognized in promoting the research and application of perovskite solar cells, but the rapid reaction of organic salts with lead iodide inevitably affects the growth of perovskite crystals, accompanied by the generation of more defects. In this study, the regulation of crystal growth was achieved in a two-step deposition method by mixing 1-naphthylmethylammonium bromide (NMABr) with organic salts. The results show that the addition of NMABr effectively delays the aggregation and crystallization behavior of organic salts; thereby, the growth of the optimal crystal (001) orientation of perovskite is promoted. Based on this phenomenon of delaying the crystallization process of perovskite, the "slow-release effect assisted crystallization" is defined. Moreover, the incorporation of the Br element expands the band gap of perovskite and mitigates material defects as nonradiative recombination centers. Consequently, the power conversion efficiency (PCE) of the enhanced perovskite solar cells (PSCs) reaches 20.20%. It is noteworthy that the hydrophobic nature of the naphthalene moiety in NMABr can enhance the humidity resistance of PSCs, and the perovskite phase does not decompose for more than 3000 h (30-40% RH), enabling it to retain 90% of its initial efficiency even after exposure to a nitrogen environment for 1200 h.

Silicon heterojunction (SHJ) solar cells are renowned for their high efficiency. However, SHJ solar cells are susceptible to various contaminants, leading to significant performance degradation when exposed to damp-heat conditions (e.g., 85 degrees C and 85% relative humidity). Sodium (Na) has been identified as one of the main con-tributors to degradation in silicon solar modules subjected to damp-heat conditions. This work investigates the role of an ultra-thin AlOx capping layer (-10 nm) in preventing the failure in SHJ cells caused by Na-related contaminants. NaCl is applied directly to the solar cell, and the unencapsulated cell undergoes a damp heat test at 85 degrees C and 85% relative humidity (DH85). It is found that without the AlOx barrier layer, the SHJ cells experience a relative reduction in power of-30%rel after only 20 h at DH85. Both the front and rear sides of the cell degrade when exposed to NaCl. This is primarily due to a deterioration of the Ag contact resulting in increased series resistance (Rs), and decrease in fill factor (FF), and an increase in recombination, leading to a significant drop in open-circuit voltage (Voc), particularly when NaCl is applied on the rear side. However, when an AlOx barrier layer is applied to the SHJ cells, the performance losses caused by NaCl are significantly reduced to only-3.3%rel. The loss in Voc on the rear side is completely suppressed, and there is only a slight increase in Rs of-50%rel compared to-300%rel increase in Rs for cells without the AlOx barrier layer. These findings indicate that the ultra-thin AlOx barrier layer provides effective protection for SHJ cells against Na ions, mitigating both Rs and recombination losses. This AlOx barrier layer depositing method is compatible with existing industrial mass-production ALD tools and thus presents a viable solution at the cell level for SHJ cells.

Short-wavelength ultraviolet (UV) photons adversely affect hydrogenated amorphous silicon thin films, as well as on silicon heterojunction (SHJ) solar cells and modules. This research examines the impact and mechanisms of photon-induced performance changes. UV A exposure disrupts Si–H bonds, significantly reducing hydrogen content in both intrinsic and doped hydrogenated amorphous silicon (a-Si:H) films. This disruption impairs the interface passivation effect, leading to the degradation of SHJ solar cells and modules, primarily indicated by a decrease in open-circuit voltage (Voc) and fill factor (FF). UV irradiation from the front side of SHJ solar cells reduces Voc and FF by 1.38

Crystalline silicon solar cells capture over 95 % of the photovoltaic market, supported by a well-established industrially framework. Key determinants for their practical deployment include increased photovoltaic conversion efficiency, reduced production costs, and improved stability. However, the efficiency enhancement is limited by parasitic absorption, a consequence of doped silicon layers. In response, dopant-free carrier selective contact silicon solar cells have emerged as a focal point of interest, offering benefits such as sub-200 °C processing temperatures, ease of material control, and superior field passivation. The utilization of wide-bandgap carrier-selective materials in silicon-based solar cells represents a burgeoning area, showcasing significant potential to approach the theoretical efficiency for solar cells. Nevertheless, the challenges are persisting in terms of controlling carrier concentration and work function, constructing high-efficiency devices, and ensuring environmental stability. These challenges continue to impede progress in this field. This article initially presents the operational principles and the current advancement status of dopant-free silicon solar cells, subsequently delving into the latest developments in their structural design and research. It further discusses the challenges and opportunities for further study, highlighting the breakthroughs required for the realisation of high-efficiency, high-stability solar cells and dual-sided power generation technology.

Bifacial passivated emitter and rear cells (PERC) currently have the highest share in the photovoltaic market. However, heterojunction (HJT) and tunnel oxide passivated contact (TOPCon) solar cells are expected to gain significant market share shortly. Despite technological advancements, concerns about the reliability of HJT and TOPCon technologies when deployed in the field still need to be addressed. This work investigates the impact of sodium chloride (NaCl) on damp-heat-induced degradation in bifacial HJT, PERC, and TOPCon solar cells by exposing the solar cells to NaCl before damp heat (DH) testing. It is found that among all investigated cell technologies, TOPCon solar cells degrade the most with maximum power (P-max) loss of up to similar to 75%(rel), followed by HJT (P-max drops similar to 50%(rel)), and PERC cells (P-max drops only similar to 10%(rel)) after 20 h of DH testing, mainly attributed to an increase in R-s on the front side of TOPCon cells, both sides of HJT cells and the rear side of PERC cells. The front of the PERC and the rear of the TOPCon solar cell are found to be stable. The rise in R-s is attributed to the corrosion of the metal contact, which is caused by a high amount of Na+ and Cl- ions penetrating the metal contact. This corrosion leads to increased porosity, detachment of the contact from the silicon interface, and increased recombination loss in some cases. These results are crucial for all cell technologies as they highlight the potential failures that could occur in the field. Na+ and/or Cl- ions are common contaminants present in solar glass, human fingerprints, soldering flux, rainwater, soil/dust, and seawater. During field operation, these ions have the potential to penetrate and directly interact with solar cells. In our view, the preferred solution is for the solar cells to be corrosion-resistant, which can be rapidly assessed using the method presented in this work.

This paper reports the results of an international interlaboratory comparison study on light‐ and elevated temperature‐induced degradation (LETID) on crystalline silicon photovoltaic (PV) modules. A large global network of PV module manufacturers and PV testing laboratories collaborated to design a protocol for LETID detection and screen a large and diverse set of prototype modules for LETID. Results across labs indicate the reproducibility of LETID testing is likely within ±1% of maximum power (P MP ). In intentionally engineered LETID‐sensitive modules, mean degradation after the prescribed detection stress is roughly 6% P MP . In other module types the LETID sensitivity is smaller, and in some we observe essentially negligible degradation attributable to LETID. In LETID‐sensitive modules, both open‐circuit voltage (V OC ) and short‐circuit current (I SC ) degrade by a roughly similar magnitude. We observe, as do previous studies, that LETID affects each cell in a module differently. An investigation of the potential mismatch losses caused by nonuniform LETID degradation found that mismatch loss is insignificant compared to the estimated loss of cell I SC , which drives loss of module I SC . Overall, this work has helped inform the creation of a forthcoming standard technical specification for LETID testing of PV modules, IEC TS 63342 ED1, and should aid in the interpretation of results from that and other LETID tests.

Extracting the parameters, energy level and electron-to-hole capture cross-section ratio, of efficiency-limiting bulk defects in silicon solar cells is a critical step in identifying those defects and potentially eliminating their impact. Typically, this is achieved on specially prepared test structures. However, in some cases, this is not possible, especially in mass production lines when only completed solar cells are available. In this study, a method that is based on temperature-dependent Suns-Voc measurements is introduced to extract the defect parameters in metalized solar cells. The method is validated by comparing the parameters of the boron-oxygenrelated defect extracted from cells and those extracted from wafers using the commonly used temperatureand injection-dependent lifetime spectroscopy. It is shown that this method has the benefit of a more accurate lifetime at low injection levels compared with photoconductance-based lifetime measurement since it is not impacted by minority carrier traps. The proposed technique is then applied to determine the parameters of the defect causing light-induced degradation in gallium-doped silicon solar cells. We determined an energy level, with respect to the intrinsic level, of -0.26 +/- 0.04 eV and a capture cross-section ratio of 34 +/- 2 for this defect. Finally, a sensitivity analysis is performed by considering the system's limited measurement temperature range. The findings demonstrate the potential of the temperature-dependent Suns-Voc method as a fast and easy-toapply method for defect characterization in metalized cells.

Illuminated solar cells are susceptible to various degradation mechanisms that can act to reduce the total energy yield when deployed. One potentially severe form is an increase in carrier recombination in the surface regions. This effect has been reported at both the undoped rear surface and phosphorous diffused emitter of PERC solar cells. This work investigates the influence of a range of surface conditions on the surface-related degradation (SRD) behaviour in PERC solar cells. It is shown that SRD is strongly affected by the doping profile of phosphorous emitters, the use of thin thermal oxides with SiNx:H dielectric passivation layers, the substrate material, and the configuration of the rear surface passivation. It finds that more lightly doped emitters result in more front side SRD, with its extent increasing with the introduction of the SiO2/SiNx:H surface passivation layers. Czochralski silicon (Cz-Si) wafers were observed to be significantly more susceptible to surface degradation than multi-crystalline silicon (mc-Si) wafers, which we attribute to less trapping of hydrogen in the bulk of those substrates. On the rear side of PERC cells, surface degradation was only observed in structures that incorporated the combination of SiO2/SiNx:H rear layers. No SRD was observed in the existing Al2O3/SiNx:H technology used in the industrial PERC cells studied. However, the results presented have implications for future commercial solar cell technologies, which are transitioning towards lightly doped emitters and commonly incorporate thermal oxides for surface passivation.

Light-induced electroplating of Al as the front electrode on the n-type emitter of Si solar cells is proposed as a substitute for screen-printed Ag. The advantages and disadvantages of Al over Cu as the front electrode are discussed. The power of a green laser used for patterning of the SiN x antireflection coating is optimized. Conditions for removal of laser damage and contamination on the laser-patterned surface are identified. The effect of plating temperature and post-annealing temperature on Al morphology and resistivity are investigated. Several plating additives are explored to improve the morphology and resistivity of the Al film. Nicotinic acid produces the lowest resistivity of 3.1 μ Ω-cm. However, the lowest contact resistivity between light-induced Al and Si is 69 mΩ-cm 2 due to laser-induced damage to the emitter. The Al film spikes through the thin n-type emitter when annealed at 500 °C causing cell failure. The process reproducibility is also poor due to atmospheric moisture.

Many research show that UV degrades the solar cell and module power. In this work, we study the UV stability of mc-Si bifacial PERC solar modules with different industrial silicon nitride (SiNx) passivation. We find that with exposure to UV at 60 °C, both VOC and JSC decrease then stabilize. The quantum efficiency analysis shows decreased response in both short (blue loss) and long (base collection loss) wavelength range. It infers that deteriorations were not only at passivation layers, but also in the silicon bulk, caused by UV-induced degradation and possible LeTID. No significant difference in degradation has been found between front and rear passivation, or between different PECVD, respectively. While thermal oxidation process employed in mass production effectively improved UV resistance.

Black silicon texturing has been considered to be a promising wafer texturing technology and can effectively improve the short-circuit current and, thus, power conversion efficiency, which has been widely used in the multicrystalline silicon photovoltaic industry. In this article, we propose a new method to "recognize" the black silicon morphology from the scanning electron microscope (SEM) images and to predict the resultant reflectance. ImageJ software was applied to recognize and analyze the SEM images for the first time, to obtain the acid-etched pit parameters. Then, we applied the recognized parameters into the sigmoid-Boltzmann equation to obtain an accurate distribution of the pit size. Finally, a modified model has been established to describe the exponential relations between the reflectance and the ratio of pit depth d over wavelength lambda (d/lambda), pit size, and pit coverage proportion. For the typical pit size 500-800 nm in mass production, its depth is about half of the wavelength lambda. Thus, we can predict the reflectance of the black silicon surface precisely, by monitoring their SEM images. The average reflectance deviation between the measured and the predicted reflectance is similar to 3.7% relatively.

This paper focuses on optimization of the light-induced Al plating process to promote a dense adherent film to the Si solar cell as the front electrode. Electrochemical capacitance-voltage and sheet resistance measurements were used to optimize the laser patterning process for the SiN x layer. A recipe to remove contaminants and laser damage on the Si surface after SiN x patterning was developed. Atomic force microscopy revealed the minimum etch time to remove all the original Si surface which was damaged and contaminated. Various plating conditions including temperature, plating voltage, and light intensity were investigated. The lowest Al resistivity obtained is 4×10 -6 Ω-cm, which is comparable to that of electroplated Cu.

In the past few years, a hot topic in both research and industrialization of p-type multi-crystalline silicon (mc-Si) solar cells is to investigate the mechanism, measurement and mitigation of the light- and elevated temperature-induced degradation (LeTID), which has been found to be a bulk-sensitive degradation behavior and is dependent on the degradation condition. In this paper, we study the influence of silicon bulk property on LeTID from five representative positions along a relative low resistivity (0.82-1.33 51 Omega cm) p-type me-Si brick. The evolution of degradation and regeneration under different laser illumination conditions are investigated. Identical defect capture cross section ratio k values of similar to 35 at mid-gap along the brick height are found. For the first time, the activation energy for degradation (E-a,E-deg) and regeneration (E-a,E-reg) along the brick are studied, which shows E-a,E-deg = E-a,E-reg and a tendency of larger values towards the brick bottom. These results indicate that the LeTID in the whole brick might be induced by a single defect and thus mitigated in a single manner. Besides, a laser illumination of 45 kW/m(2) at 142 degrees C for 100 s is able to induce over 90% degradation for all wafers, which could be used as a universal and fast LeTID test condition.

Monitoring the light and elevated temperature induced degradation (LeTID) of crystalline silicon solar cells is becoming a standard quality control point in manufacturing. The conventional method light soaking shows several drawbacks, such as the slow response, the large footprint, and low throughput, which limit the LeTID test sampling rate, especially in GW scale mass production. Besides light soaking, LeTID can be induced by applying forward bias upon the P-N junction, which is the current injection. Here, we prove that the current injection can induce the same level of LeTID as light soaking does. In this way, a wide range of current induced degradation (CID) conditions are established on a commercialized equipment. Regarding to the multi crystalline PERC solar cells, 3.5 A-105 °C (for 157 mm cells) is chosen as an accelerated condition to induce LeTID, which is supported by simulations and experimental data.