Silicon Heterojunction Cells Research Articles

Ultrathin Self-Assembled Monolayer for Effective Silicon Solar Cell Passivation.

Passivation technology is crucial for reducing interface defects and impacting the performance of crystalline silicon (c-Si) solar cells. Concurrently, maintaining a thin passivation layer is essential for ensuring efficient carrier transport. With an ultrathin passivated contact structure, both Silicon Heterojunction (SHJ) cells and Tunnel Oxide Passivated Contact (TOPCon) solar cells achieve an efficiency surpassing 26%. To reduce production costs and simplify solar cell manufacturing processes, the rapid development of organic material passivation technology has emerged. However, its widespread industrial production is hindered by environmental safety concerns, such as strong acid corrosion and biological and ecological safety issues. Here, we discovered a low-cost self-assembled monolayer (SAM) hole-selective transport material known as 2PACz ([2-(9H-carbazol-9-yl) ethyl] phosphonic acid) with phosphate groups to form c-Si solar cells for the first time. The ultrathin film of 2PACz with phosphate groups can establish strong and stable P-O-Si bonds on the silicon surface. Meanwhile, like 2PACz, a uniform ultrathin film with a carbazole function group can offer electron-localizing and thus hole-selective properties, which provides ideas for studying dopant-free silicon solar cells. As a result of such interfacial passivation engineering, it plays an important role in repairing porous structures, such as pyramid-textured silicon surfaces, and cutting losses during the commercialization of c-Si solar cells. Crucially, this advancement offers insights for the development of new high-efficiency ultrathin film passivation methods in the postsilicon era.

Improved electrical contact properties in Indium-free silicon heterojunction solar cells with amorphous SnO2 TCO layers

Silicon heterojunction (SHJ) solar cells are recognized as one of the most efficient architectures in silicon-based photovoltaic devices. However, the reliance on indium (In)-based transparent conductive oxides (TCO) is anticipated to constrain their production capacity due to the critical and economically volatile nature of In. Recently, low-temperature-grown amorphous SnO2 (a-SnO2) films have been explored as an earth-abundant alternative TCO material. In this study, we examine the electrical contact properties of a-SnO2 layers employed as TCO layers in SHJ cells, focusing on their interaction with the underlying carrier selective contact layers. Our findings indicate that a stack of doped amorphous silicon (a-Si:H) and a-SnO2 exhibits relatively high specific contact resistivity, leading to a significant reduction in the device's fill factor. To address this issue, we propose two approaches: the insertion of a thin ZnO-based TCO layer between a-Si:H and a-SnO2, and the use of nanocrystalline silicon layers in place of a-Si:H. Both approaches effectively reduce the contact resistivity, resulting in improvements in fill factor and conversion efficiency comparable to those of benchmark device with In-based TCOs. Based on these findings, we demonstrate a high-efficiency, In-free, SnO2-based SHJ cell.

Signal Components and Impedance Spectroscopy of Potential p‐Si/n‐CdS/ALD‐ZnO Solar Cells: EIS and SCAPS‐1D Treatments

AbstractA silicon heterojunction (SHJ) solar cell with the attractive and widely used atomic layer deposited (ALD)‐ZnO/n‐CdS/p‐Si configuration is examined in this work to learn more about its electrical properties. Using EIS and SCAPS‐1D, a comprehensive model of the device is created and then simulated. Theoretical aspects of the cell are examined through the use of similar electrical circuit models, focusing on the transmittance spectrum made possible by the ALD‐ZnO layer's low reflectance and high visible transmittance. In this study, the C–V tool is used to study the trap states in the silicon absorber layer under different lighting conditions and wavelengths. The doping concentration and built‐in potential are determined using the Mott–Schottky technique. In addition, the cell's properties are investigated by measuring its G–V, G–F, C–T, and C–F in different real‐world scenarios. As a means of visualizing the electrochemical impedance data, Nyquist plots—sometimes called Cole–Cole plots—are utilized. By utilizing absolute impedance and phase shifts, Bode plots are employed to examine the system's frequency response. Last, the results of the SHJ cell's spectral response measurements are given, which confirm the results of the Nyquist plots.

Perovskite/silicon tandem solar cells with bilayer interface passivation.

Two-terminal monolithic perovskite/silicon tandem solar cells demonstrate huge advantages in power conversion efficiency compared with their respective single-junction counterparts1,2. However, suppressing interfacial recombination at the wide-bandgap perovskite/electron transport layer interface, without compromising its superior charge transport performance, remains a substantial challenge for perovskite/silicon tandem cells3,4. By exploiting the nanoscale discretely distributed lithium fluoride ultrathin layer followed by an additional deposition of diammonium diiodide molecule, we have devised a bilayer-intertwined passivation strategy that combines efficient electron extraction with further suppression of non-radiative recombination. We constructed perovskite/silicon tandem devices on a double-textured Czochralski-based silicon heterojunction cell, which featured a mildly textured front surface and a heavily textured rear surface, leading to simultaneously enhanced photocurrent and uncompromised rear passivation. The resulting perovskite/silicon tandem achieved an independently certified stabilized power conversion efficiency of 33.89%, accompanied by an impressive fill factor of 83.0% and an open-circuit voltage of nearly 1.97 V. To the best of our knowledge, this represents the first reported certified efficiency of a two-junction tandem solar cell exceeding the single-junction Shockley-Queisser limit of 33.7%.

Electrical Performance, Loss Analysis, and Efficiency Potential of Industrial‐Type PERC, TOPCon, and SHJ Solar Cells: A Comparative Study

ABSTRACTCurrently, the efficiency of p‐type passivated emitter and rear contact (PERC) cells has been growing at an absolute efficiency of 0.5% per year and has reached 23%–23.5% in mass production while getting closer to its theoretical efficiency limit. n‐Type tunnel oxide passivated contact (TOPCon) and silicon heterojunction (SHJ) cells with their superior “passivating selective contacts” technology were the most interesting photovoltaics (PV) technology in the industry. The effect of different passivated contact layers with respect to their influence on the J0, J0,metal, ρc, and the carrier selectivity (S10) and the loss analysis and efficiency potential of industrial‐type PERC, TOPCon, and SHJ solar cells were studied and compared. The results showed that TOPCon structure with a high passivation performance and good optical performance is more suitable for bifacial solar cell and the highest theoretical limiting efficiency with metal shading on the n‐type Si wafer (ηb,e,h,m,max) can be achieved to 27.62%. Although SHJ structure with the highest passivation performance but the worst optical performance owing to the parasitic absorption of a‐Si:H layer and high contact resistivity, the value of ηb,e,h,m,max is 0.7% lower than that of TOPCon solar cells. PERC structure has superior optical performance than SHJ structure, but due to poor passivation performance, the ηb,e,h,m,max is only 26.42%. The next‐generation products may be heterojunction back‐contact (HBC) and TOPCon back‐contact (TBC) cells with high ηb,e,h,m,max of 28.12% and 27.99%, respectively. Exploiting a perfect passivation of the noncontact area, the wide process window and low cost are required and transferring these new concepts to industrial solar cell production will be the next major challenge.

Low‐Temperature Atomic Layer Deposition of Hole Transport Layers for Enhanced Performance and Scalability in Textured Perovskite/Silicon Tandem Solar Cells

AbstractPerovskite tandem solar cells on textured silicon hold potential for surpassing single‐junction limits and industrial compatibility. However, integrating hole‐transporting layers (HTLs) onto textured silicon poses challenges in conformal coating, low‐temperature fabrication, and perovskite solution process compatibility. Here, an atomic layer deposition (ALD) copper‐doping process is introduced to fabricate low‐temperature NiOx HTLs (ALD Cu:NiOx), tailored for textured tandems. Copper‐doping reduces hydroxyl group content and Ni3+ defects, addressing the challenge of enhancing hole conductivity while mitigating recombination loss. This advancement enables to lower the post‐annealing temperature from >300 to 200 °C, achieving compatibility with silicon heterojunction (SHJ) cells and boosting the power‐conversion efficiency (PCE) of 1.65‐eV p–i–n perovskite solar cells to 22.47%. Integrating ALD Cu:NiOx beneath conventional self‐assembled monolayer HTL on textured SHJ leads to notable PCE enhancements, from 28.6% to 30.5% for 1‐cm2 tandems (certified stabilized PCE of 30.04%) and from 23.9% to 26.4% for 8.89‐cm2 tandems. Following 1000 h of maximum‐power‐point (MPP) tracking, tandems maintain 95% of initial efficiency. Notably, losses in open‐circuit voltage and PCE due to area upscaling reduced by over 20%, attributed to ALD Cu:NiOx’s ability to enhance perovskite film wettability and minimize shunting on silicon pyramid texture, underscoring its impacts for textured tandem upscaling.

Study of the Effect of Exciton Annihilation Lifetime on Some Kinematic and Intrinsic Parameters of a Silicon Heterojunction Solar Cell (HIT), Illuminated by Monochromatic Light

In this article, with a view to improving the efficiency of photovoltaic cells, and given the promising yields of silicon heterojunction photovoltaic cells, we have, using a silicon heterojunction cell (a-Si:H/c-Si) doped with (n+p) , studied the contribution of excitons to the internal quantum efficiency of charge carriers. We then developed a detailed explanation of the energy conversion phenomena, based on an exciton-exciton annihilation process, which allows the electrons of quasiparticles to retain some of their energy. We used a numerical method for solving the charge carrier transport equations and carried out some additional calculations, which enabled us to obtain some results. These results then enabled us to study the influence of the annihilation lifetime on the charge carrier photo-current density, leading to internal charge carrier quantum yields of between 29.29768% and 77.8525%.

Development of high conducting phosphorous doped nanocrystalline thin silicon films for silicon heterojunction solar cells application

We have investigated the plasma-enhanced chemical vapor deposition growth of the phosphorus-doped hydrogenated nanocrystalline silicon (n-nc-Si:H) film as an electron-selective layer in silicon heterojunction (SHJ) solar cells. The effect of power densities on the precursor gas dissociation are investigated using optical emission spectra and the crystalline fraction in n-nc-Si:H films are correlated with the dark conductivity. With the P d of 122 mW cm−2 and ∼2% phosphorus doping, we observed Raman crystallinity of 53%, high dark conductivity of 43 S cm−1, and activation energy of ∼23 meV from the ∼30 nm n-nc-Si:H film. The n-nc-Si:H layer improves the textured c-Si surface passivation by two-fold to ∼2 ms compared to the phosphorus-doped hydrogenated amorphous silicon (n-a-Si:H) layers. An enhancement in the open-circuit voltage and external quantum efficiency (from >650 nm) due to the better passivation at the rear side of the cell after integrating the n-nc-Si:H layer compared to its n-a-Si:H counterpart. An improvement in the charge carrier transport is also observed with an increase in fill factor from ∼71% to ∼75%, mainly due to a reduction in electron-selective contact resistivity from ∼271 to ∼61 mΩ-cm2. Finally, with the relatively better c-Si surface passivation and carrier selectivity, a power conversion efficiency of ∼19.90% and pseudo-efficiency of ∼21.90% have been realized from the SHJ cells.

Structural optimization and growth of intrinsic hydrogenated amorphous silicon films by HWCVD

Although the silicon heterojunction (SHJ) solar cell is the crystalline silicon solar cell with highest conversion efficiency at present, its higher cost of production line has been a factor restricting its industrial development. The use of hot wire chemical vapor deposition (HWCVD) technology instead of the mainstream plasma enhanced chemical vapor deposition (PECVD) technology for the deposition of amorphous silicon films can effectively reduce the cost of equipment and processing, and has a bright future. In recent years, i-a-Si:H films grown by PECVD have obtained great improvement in passivation quality, whereas HWCVD technology has been neglected in this field. This has significantly limited the development and application of HWCVD technology in SHJ cell production. In this work, we exploited the differences in the films properties and microstructures deposited by various hot-wire temperatures and successfully developed a structure for the high-passivation-quality i-a-Si:H film grown by HWCVD, consisting of a buffer layer and a double-layer bulk stack. By introducing the buffer layer grown with the 1650 °C hot-wire temperature and pure silane, the effective minority carrier lifetime was improved from 2.3 ms to 7.5 ms, and a cell efficiency enhancement of 0.4%abs was obtained. By depositing the bulk layer sequentially with hot-wire temperatures of 1800 °C and 1900 °C, the passivation quality and the conductance were both improved. An effective minority carrier lifetime of 8 ms and a further cell efficiency enhancement of 0.15%abs were obtained. Finally, SHJ solar cell efficiency of 24.35% was obtained with a home-made HWCVD-based pilot SHJ cell line.

Study on the process of hydrogen-doped indium oxide for silicon heterojunction solar cell mass production

In this work, we conducted a comparative study on water vapor (H2O) process and hydrogen gas (H2) process to prepare the IMO:H films based on industrialized DC magnetron sputtering system. To dynamically control the residual H2O pressure, we installed a set of polycold coil and kept it turned on during the sputtering process. The film characteristics of Hall mobility, carrier density, sheet resistance, and transparency was investigated. The results revealed that the silicon heterojunction (SHJ) solar cell with H2 process had a higher Hall mobility and greater transparency in the 400–600 nm wavelength range resulting in a lower contact resistivity and a slight increase current density compared to the H2O process. The median efficiency (Eff) achieved with the H2 process improved by 0.09% absolute to 25.43%, mainly because of the increased Jsc and FF. And the IMO:H films with H2 process had a large basal spacing with (400) and (222) crystal planes resulting in maintaining a more stable and reliable structure at temperatures below 200 °C. After the optimization of TCO layer process, we manufactured the industrial-grade SHJ cells with max efficiency (Eff), Voc, Jsc, and fill factor (FF) values as high as 26.27%, 753 mV, 41 mA/cm2, and 86%, respectively. The IMO:H films with H2 process can thus be considered more suitable for large-scale production.

Thin silicon heterojunction solar cells in perovskite shadow: Bottom cell prospective

Perovskite/Silicon (Pero-Si) tandem with silicon heterojunction (SHJ) bottom cells is a promising highly efficient concept, which in the case of mass production will likely rely on the same wafer feedstock as the single junction Si solar cells. The thickness of these wafers is constantly decreasing for economic and sustainability reasons. We forecast that Si bottom cells for mass produced Pero-Si tandems will be based on wafers thinner than 100 μm. In our work we study challenges and opportunities related to this likely wafer thinning for the performance of the SHJ bottom cells operating in Perovskite shadow. We study SHJ cells prepared on 80 μm thick wafers in comparison to the reference cells based on 135 μm thick wafers addressing two issues: passivation and light management. Effects of passivating layer thickness, back reflector and antireflection coating are studied under AM1.5G standard test conditions, attenuated AM1.5G irradiance, and under Perovskite-filtered spectrum. We show that major wafer thickness reduction of 40% turns to only approx. 0.35%abs loss in the bottom cell efficiency. This minor loss can be reduced even further using highly technological ITO/MgF2/Ag back reflector and MgF2 anti-reflection coating. Our work shows that significant potential for Pero-Si tandems is waiting to be explored in the perovskite shadow from the SHJ bottom cell perspective.

LIFT metallization as an alternative to screen-printing for silicon heterojunction solar cells

The electrical characteristics of solar cells are significantly influenced by the metallization process, making it a crucial step. Screen printing is the standard metallization technique, but there is an increasing interest in the development of methods that allow more versatility, higher process control, and a more efficient use of the expensive metallic pastes used. We focus here on the comparison between the standard screen-printing method, and Light-Induced Forward-Transfer (LIFT), a non-contact, very precise technique, able to transfer volumes down to picolitres. The high flexibility, using free-form designs that do not depend on any mask or physical support, and the efficient use of the metallic paste with almost no waste, are other characteristics that point out LIFT as a very promising alternative. In this paper we include the electric characterization of contacts, and solar silicon heterojunction (SHJ) cells metalized with both techniques. The results show a slightly better efficiency for the screen-printed cells, but good series resistance and fill factor values imply that LIFT is a promising alternative for device metallization.

Nanocrystalline Silicon Layers for the Application in Silicon Heterojunction Solar Cells

After application in thin-film silicon tandem solar cells and in lab-scale silicon heterojunction (SHJ) devices, doped nanocrystalline silicon (nc) layers now arrived on the industrial stage. Despite their challenging deposition, the benefits they hold with respect to even higher device performance compared to their amorphous counterparts are significant and justify additional effort. In this contribution we report on developments towards industrially applicable processes for n- and p-doped silicon layers, nc-Si(n) and nc-Si(p), and their implementation in SHJ cells. Our investigation focuses on the impact of deposition temperature (Tdep) and the need for a thin oxide layer to promote fast nucleation of thin, sufficiently crystalline, doped nc-Si films in a single deposition chamber powered at 13.56 MHz. We identified main challenges for thin film and contact engineering and reached efficiencies of 23.0% with n- and 23.1% with p-type nc-Si approaching cell performances of our process of record based on amorphous Si (a-Si) layers.

Evaluating the Practical Efficiency Limit of Silicon Heterojunction–Interdigitated Back Contact Solar Cells by Creating Digital Twins of Silicon Heterojunction Solar Cells with Amorphous Silicon and Nanocrystalline Silicon Hole Contact Layers

Improving power conversion efficiency (PCE) in photovoltaics has driven innovative approaches in solar cell design and technology. Silicon heterojunction (SHJ) solar cells exhibit advantages in PCE due to their effective passivating contact structures. SHJ–interdigitated back contact (SHJ–IBC) solar cells have the potential to surpass traditional SHJ cells, attributed to their advantage in short‐circuit current (JSC). Herein, Silvaco Atlas technology computer‐aided design is used to create digital twins of high‐efficiency SHJ solar cells with amorphous silicon and nanocrystalline silicon hole selective contact (HSC) layers. Using parameters from digital twins of SHJ solar cells, the practical efficiency limit of SHJ–IBC solar cells is assessed. The results show that SHJ–IBC cells can achieve potential efficiencies of 27.01% with amorphous HSC and 27.38% with nanocrystalline HSC. Further efficiency augmentation to 27.51% can be achieved by narrowing the gap from 80 to 20 μm. This study not only advances comprehension of SHJ–IBC solar cells but also provides insights into optimizing geometrical configurations for improved performance. The utilization of digital twins provides a valuable tool for predicting and evaluating the performance of SHJ–IBC solar cells, contributing substantively to the ongoing development of high‐efficiency photovoltaic technology.

Potential‐induced degradation in bifacial silicon heterojunction solar modules: Insights and mitigation strategies

AbstractPotential‐induced degradation (PID) may be a serious concern in photovoltaic (PV) modules and plants, particularly when approaching high system voltages (1500+ V). Here, we investigate PID occurring in bifacial rear‐emitter silicon heterojunction (SHJ) solar cells encapsulated in a glass/glass (G/G) module configuration with ethylene vinyl acetate (EVA) as an encapsulant. PID testing was performed at 85°C in 85% relative humidity (RH), and the solar cells were subjected to −1 kV and +1 kV for up to 800 h. SHJ cells were found to degrade when subjected to −1 kV, and to a lesser extent when left unbiased in damp heat (DH) conditions, while the application of +1 kV prevented degradation. Although prone to PID after extended test durations, the SHJ mini‐modules investigated in this study noticeably passed the industry standard (IEC 61215:2021) PID test of 96 h. The degradation was primarily characterized by losses in short‐circuit current (ISC) at the front side, followed by fill factor (FF) and open‐circuit voltage (VOC). A cross‐sectional transmission electronic microscopy analysis of the laminates subjected to −1 kV highlighted a transport of sodium (Na) through the transparent conductive oxide (TCO), reaching the amorphous Si/TCO interface. The samples tested in DH conditions and with positive PID test conditions did not exhibit such a migration of Na. To account for these observations, we updated a previously proposed model describing the sensitivity of SHJ cells to water. In our degradation model, moisture in the module corrodes the glass, creating sodium hydroxide (NaOH) that then percolate through the EVA before reaching the SHJ cell. The application of a high negative bias amplifies the previous mechanism by increasing the availability of Na+ and also enhances the drift of Na+ through the EVA to the cell. Finally, we demonstrate that PID can be mitigated or suppressed at the module level by using a high‐volume resistivity encapsulant with a low water vapor transmission rate (WVTR) or by encapsulating SHJ solar cells in a configuration impermeable to water (e.g., using an edge sealant).

Defining specifications for accurate Metal/TCO specific contact resistivity measurements by TLM in silicon heterojunction devices

Measuring specific contact resistivity (ρc) in test vehicles representative of the final solar cell is critical for interface engineering in high efficiency devices such as silicon heterojunction (SHJ) solar cell. The Transfer Length Method (TLM) is commonly used for layer sheet resistance (Rsheet) and ρc evaluation and is valid for samples with charge transport confined in one conductive layer only. For metal/Transparent Conductive Oxide (TCO) interface ρc evaluation from SHJ cells precursors, there is a need to prevent any contribution from the conductive c-Si. In this work, we investigated by simulation and experimental approach the parameters restricting the current confinement inside the TCO. The first one is the mid-gap trap density (Dit) at the a-Si:H/c-Si interface which has no strong impact on current confinement on simulated TLM test structures. The second one is the variation of the activation energy (Ea=Ec−EF) of the a-Si:H contact layers. Both simulated and experimental results have demonstrated that three current distribution regimes are possible in the TLM test structure depending on the Ea value with only one regime, for Ea between 0.6 and 1.4 eV, enabling to isolate the metal/TCO interface. This condition is mandatory to maintain a sufficiently high potential barrier for electrons at the interfaces a-Si:H(p)/a-Si:H(i)/c-Si(n) and thus lateral current in the TCO layer to apply TLM on SHJ devices.

Addressing sodium ion-related degradation in SHJ cells by the application of nano-scale barrier layers

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 °C and 85% relative humidity). Sodium (Na) has been identified as one of the main contributors 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 °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.

Application of interface treatment at different position p-nc-Si:H hole collector of silicon heterojunction cells

The hole collector in silicon heterojunction cells serves not only as an integral component of the p/n junction, determining the strength of the built-in electric field, but also as a layer responsible for hole transport, thereby affecting carrier transport capacity. To enhance carrier extraction and transport properties of the hole collector, various interface treatments have been employed on p-type nanocrystalline (p-nc-Si:H) hole collectors. Through an examination of characteristics such as dark conductivity, crystallinity, and contact resistance, the impact of interface treatment on p-nc-Si:H hole collectors is clarified. Furthermore, considering distinct requirements for the hole collector at different locations, interface treatment processes are optimized accordingly. The introduction of interface treatment on p-nc-Si:H hole collectors has demonstrated significant enhancement of both front and rear junction cell efficiencies, which increased from 17.74% to 21.61% and from 16.83% to 20.92%, respectively.

Investigation into fill factor and open-circuit voltage degradations in silicon heterojunction solar cells under accelerated life testing at elevated temperatures

There are many reports on open-circuit voltage (VOC) degradation but limited reports on fill factor (FF) degradation in silicon heterojunction (SHJ) solar cells which are either subjected to an accelerated testing condition or to a field condition. The factors contributing to FF loss and VOC loss due to aging required a thorough investigation to gain insight into potential loss mechanisms and the approaches to mitigate them. In this context, we subjected SHJ solar cells of the same structure to varying accelerated testing conditions (i.e. exposure temperature of 90 °C versus 120 °C, under 1-sun illumination) in experiment 1 to 3 of this work. The SHJ cells exposed to a temperature of 90 °C were nearly stable in performance even after 2000 h while those exposed to 120 °C degraded significantly in FF. Device measurements and analysis revealed that the FF degradation was due to an increase in series resistance (Rs) and hole collection barrier. In experiment 4, the effect of device structure was investigated by subjecting cells with only front-side indium tin oxide (ITO) and those with both-sides ITO to the same accelerated testing conditions at a temperature of 90 °C under 1-sun illumination. The result obtained revealed that SHJ cells with both sides ITO were nearly stable in electrical performance while those with only front ITO degraded in performance, dominated by VOC loss. The VOC loss was perhaps due to loss of passivation at the rear-side of the cells.

Low-temperature metallization & interconnection for silicon heterojunction and perovskite silicon tandem solar cells

In this work, we present results on various low-temperature approaches for the metallization and interconnection of high-efficiency solar cells as silicon heterojunction (SHJ) or perovskite silicon tandems. By using fine line screen printing for the cell metallization and Ag-free or -reduced interconnection technologies, we demonstrate the potential of these approaches both for SHJ and perovskite silicon tandem cells. Furthermore, low-temperature (LT, ∼200 °C) or ultra-low-temperature (ULT, ∼150 °C) processes are utilized for metallization and interconnection to treat these temperature-sensitive solar cells with a reduced energy consumption. We compare LT soldering of SHJ cells with Pb-free alloys to state-of-the-art soldering processes and interconnection with electrically conductive adhesives (ECAs). For successful module integration of perovskite silicon tandem solar cells, these findings provide the basis to build full-size tandem modules with different interconnection technologies.