Perovskite solar cells with a wide bandgap (WBG) perovskite absorber of 1.68 eV are fabricated and their performance evolution under accelerated stressing conditions are compared with 1.61 eV reference devices. The cells are processed entirely with scalable deposition methods, to guarantee their relevance for industrial application. Different stress tests, following the International Summit on Organic Photovoltaic Stability (ISOS) protocols, are performed, namely prolonged exposure to light (ISOS-L1), heat (ISOS-D2) and a combination of these (ISOS-L2). First, the ISOS-L1 test highlights the excellent stability of the chosen WBG composition, with minimal degradation after 60h. Secondly, the ISOS-D2 test led to a more significant degradation of the WBG cells, with only 80% efficiency retained after 95h. The main cause of degradation was found to be interface-related, specifically the formation of a charge transport barrier at the perovskite/electron transport layer interface, while the perovskite absorption properties remained unaffected by the stress test. Finally, the ISOS-L2 test led to an even faster degradation, with only 80% efficiency retained after 35h. There, the perovskite absorber itself was found to be significantly degraded due to the combined action of light and heat. Altogether, this study highlights the main degradation pathways in WBG perovskite cells while showing the importance of diversified and combined stresses in evaluating their stability.

Perovskite mini-modules with two ETL compositions—thick ETL1 (LiF/C 60 /BCP) and thin ETL2 (LiF/C 60 /LiF)—were measured outdoors for over three years to assess long-term performance.

Perovskite mini-modules with two ETL compositions—thick ETL1 (LiF/C 60 /BCP) and thin ETL2 (LiF/C 60 /LiF)—were measured outdoors for over three years to assess long-term performance.

Passivation is playing a significant role in achieving excellent performance in perovskite solar cells. However, traditional characterization in this context is often limited to the analysis of current-voltage (IV) and sometimes the analysis of superficial chemical properties via UV or X-ray photoelectron spectroscopy (UPS or XPS). This is not sufficient in order to provide a full understanding of the passivation impact and target the best passivation strategies. In this work, a more developed characterization protocol is introduced, aiming at establishing a clearer link between nano-scale electrical properties and macro-scale device characteristics. Traditional IV measurements are combined with admittance spectroscopy (AS) and deep-level transient spectroscopy (DLTS) for the analysis of charge-related performance losses and with Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS) to complete the understanding of ionic accumulation at the perovskite interfaces. This protocol is tested on two experimental devices, a reference MAPI-based p-i-n perovskite cell and the same cell passivated at both perovskite interfaces. First, IV measurements show an increase of both Voc and FF of approximately 10% for the passivated cell, with an absolute efficiency increase of 4%. AS measurements suggest that the higher FF in the passivated sample cannot be attributed to a lower series resistance, but possibly to a lower diffusivity of some ionic species present at the interface. Analysis of the DLTS response yields an activation energy of 0.37 eV. The pre-exponential factor for these ions is lower for the passivated cell, which is also suggested by the higher Voc. Finally, preliminary ToF SIMS results showcase different ionic species that accumulate at the perovskite interfaces. Overall, this novel characterization approach enables a rather comprehensive understanding of the device and points to leads for future work about passivation for perovskite solar cells.

Hybrid concentrated solar power/photovoltaic systems (CSP/PV) combine the advantages of the two separate systems while reducing their drawbacks. The design of such a hybrid system is challenging due to the various trade-offs between the thermal and electrical performance, and the overall system complexity. A reliable simulation model that includes all relevant optical, thermal, and photovoltaic aspects, can therefore be extremely useful to analyse the combined system performance and fine-tune the various design parameters. While multi-physics modelling of photovoltaic systems is well established, this is not the case for hybrid CSP/PV. In this paper, a novel multi-physics framework is presented for a hybrid system consisting of a parabolic trough with integrated PV cells covered by a dichroic coating, focusing incident sunlight towards a thermal receiver. Instead of monofacial PV cells, bifacial cells are considered for harvesting also the diffuse and ground reflected light at the back of the trough. The presented framework relies on an existing simulation tool for PV modules, that is combined with a ray-tracer that includes the spectral beam splitting functionality of the coating, and a novel 1.5D thermal model for the receiver tube. Long term outdoor monitoring results are used to predict the averaged, time-resolved annular thermal and electric energy yield of the system. This energy production is compared for three different multilayer coating designs with an increasing amount of (TiO 2 , SiO 2 ) layers. These results show that the amount of reflected sunlight towards the thermal receiver can be enhanced at the expense of the transmitted sunlight towards the PV cells, when a higher number of layers are used. The reduction of the incident power on the PV cells is however almost fully compensated by the enhanced spectral match of the transmitted light with the spectral response of the considered bifacial cells, in addition to the enhanced cell efficiency due to the lower thermalization losses. This results in superior system efficiency, for the application scenario where the generated thermal energy is also converted in electrical energy, and geographical locations with sufficient direct sunlight; a conclusion that is drawn from comparing the total electrical energy yield in Spain and Belgium, as a function of the thermal to electrical conversion fraction.

A multifaceted characterization approach is proposed, aiming to establish a link between nanoscale electrical properties and macroscale device characteristics. Current-voltage (I-V) measurements are combined with admittance spectroscopy (AS) and deep-level transient spectroscopy (DLTS) for the analysis of charge-related performance losses with time-of-flight secondary-ion mass spectrometry to complete the understanding of ionic motion in the device. This is applied to the study of surface treatment in perovskite solar cells, which implements several strategies to improve band alignment, perovskite grain growth, and chemical passivation. An increase of both open-circuit voltage (Voc) and fill factor of respectively 90 mV and 11% is shown after surface treatment, with an absolute efficiency increase of 4%. AS measurements, coupled with a lumped elements model, rule out the impact of transport layers as the origin of the performance improvement, rather pointing toward a reduction in ionic resistance in the perovskite bulk. Analysis of the DLTS response yields an activation energy of 0.41 eV, which is likely related to the same ionic mechanism discovered with AS. Finally, both of these techniques enable to show that the surface treatment main contribution is to reduce ion-related recombination of charge carriers. Characterization is used for the study of surface treatment in perovskite solar cells. Current-voltage measurements show a 90 mV increase in open-circuit voltage, 11 % increase in fill-factor and 4 % increase in efficiency. Capacitance-based measurements show an increase in ionic resistance in the perovskite bulk and an activation energy of 0.41 eV, pointing toward a reduction in ion-assisted charge carrier recombination.image (c) 2024 WILEY-VCH GmbH

Lithium fluoride (LiF) is currently a very popular dielectric material used as a passivation or transport layer in a variety of applications, especially in high-efficiency solar cells. Despite this, its conduction properties and interface behavior with silicon remain largely unexplored. In this work, a LiF metal–insulator–semiconductor (MIS) structure is fabricated and characterized, and its properties are compared to the well-understood aluminum oxide (Al2O3) MIS structure. First, a higher current density in LiF compared to Al2O3 is highlighted, as well as its PN junction-like behavior with n-type silicon (n-Si), being rather unconventional for a dielectric layer. C–V measurements showcase the likely presence of an interface defect, causing an increase in the apparent doping and a shift in the flatband voltage VFB by +70 meV. This defect is found to be of the acceptor type, which renders the interface fixed charge more negative and improves the field-effect passivation in the case of a negative Qf. Finally, a density of interface states Dit≈2×1011 cm−2 eV−1 was found for LiF/n-Si, which is a low value showing appropriate chemical passivation at the interface. Overall, this work enables us to shed more light on the interface properties of LiF on n-Si, which is an essential step toward its wider use in state-of-the-art solar cells and other silicon-based devices.

In this work, we show the integration of polysilicon-based passivating contacts in plated bifacial n-type PERT (passivated emitter and rear totally diffused) solar cells. We show the viability of n-PERT cells using two-side passivating contacts with two-side plated nickel/silver metallization. Compared with commercially available "TOPCon" cells with rear side passivated contacts only, n-PERT cells with both side passivated contacts should enable the exploitation of the full potential of passivated contacts. We show that both n-poly and p-poly were applied and co-plated successfully on both sides of n-PERT solar cells. Considering the potential parasitic absorption losses on the front side of the device originating from p-poly, we applied selective p-poly by patterning. We compared two patterning methods for front side polysilicon: the masking and etch approach using inkjet printing and a simple and cost-effective patterning method using UV laser oxidation. A best efficiency of 22.7% has been achieved with these cells so far on large area (244.3 cm(2)) n-type Cz, with a potential efficiency above 24%. Some of these co-plated bifacial cells have been processed into one-cell laminates using smart wire interconnection (SWCT) technology. These have passed thermal cycling (TC) tests as defined in IEC61215.

Poly-Si/SiOx passivating contacts enable the manufacturing of highly-efficient Si solar cells, but their fabrication commonly relies on an extra high-temperature process such as dopant diffusion or thermal annealing for achieving excellent passivation and contacting properties. This extra process is eliminated in the fired passivating contact (FPC) approach used for simplified fabrication of poly-Si/SiOx passivating contacts. Instead, FPCs rely on the thermal budget of the fast/short and high-temperature firing process used for metallization of solar cells to achieve similar final properties. Despite this, compatibility of FPCs with industrially viable metallization techniques has not been demonstrated yet, which is studied in this work for fire-through Ag screen-printing and Ni/Ag plating. With screen-printing, low recombination current density (J(0)) down to 4.9 fA/cm(2), low contact resistivity between the Ag contacts and the FPC (rho(c,m)) down to 7.2 m Omega.cm(2), and Ohmic transport through the FPC including the SiOx film were achieved using wet-chemically grown SiOx. Nevertheless, J(0) of metallized regions (J(0,m)) exceeded 1000 fA/cm(2). Reducing J(0,m) was attempted by mitigating the blistering observed in FPCs, but J(0,m) remained high. With Ni/Ag plating, excellent surface passivation with J(0) down to 2.7 fA/cm(2) and very low J(0,m) < 50 fA/cm(2) were achieved, but no Ohmic contacts could be obtained. Integration of screen-printed FPCs in large-area n-TOPCon solar cells was also demonstrated, yielding average efficiencies of 18.4%, limited mainly by the high J(0,) (m) and series resistance of the FPCs. The results presented reveal the challenges for the industrialization of FPCs and provide valuable insights for tackling these.

In situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films by low pressure chemical vapor deposition (LPCVD) were studied in this work for the fabrication of poly-Si passivating contacts. In situ doping was targeted for enabling the full potential of the high-throughput LPCVD technique, as it could allow leaner fabrication of industrial solar cells featuring poly-Si passivating contacts than the more common ex situ doping routes. By careful optimization of the deposition temperature and the flows of the carrier gas (H-2) and the dopant precursor (PH3), high doping in the poly-Si layers was achieved with active P concentrations up to 1.3.10(20) cm(-3) . While reduction in the deposition rate (r(dep)) and thus in the throughput is a known problem when growing in situ P-doped films by LPCVD, this reduction could be limited, and the resulting r(dep) was equal to 0.078 nm/s. The developed poly-Si films were characterized both structurally and in terms of their passivation potential in poly-Si contacts. The latter yielded recombination current densities down to 1.5 fA/cm(2) in passivated (J(0, p)) and 25.6 fA/cm(2) in screen-printing metallized (J(0, m)) regions on saw-damage removed (SDR) Cz-Si surfaces, accompanied by a contact resistivity (rho(c,m)) of 4.9 m Omega.cm(2). On textured Cz-Si surfaces, the corresponding values were J(0, p) = 3.5 fA/cm(2), J(0,m )= 56.7 fA/cm(2), and rho(c,m) = 1.8 m Omega.cm(2). Optical impact of the developed poly-Si films was also assessed and a short circuit density loss of 0.41 mA/cm(2) is predicted per each 100 nm of poly-Si applied at the rear side of solar cells.

We use temperature-dependent contact resistivity (rho c) measurements to systematically assess the dominant electron transport mechanism in a large set of poly-Si passivating contacts, fabricated by varying (i) the annealing temperature (Tann), (ii) the oxide thickness (tox), (iii) the oxidation method, and (iv) the surface morphology of the Si substrate. The results show that for silicon oxide thicknesses of 1.3-1.5 nm, the dominant transport mechanism changes from tunneling to drift-diffusion via pinholes in the SiOx layer for increasing Tann. This transition occurs for Tann in the range of 850 degrees C-950 degrees C for a 1.5 nm thick thermal oxide, and 700 degrees C-750 degrees C for a 1.3 nm thick wet-chemical oxide, which suggests that pinholes appear in wet-chemical oxides after exposure to lower thermal budgets compared to thermal oxides. For SiOx with tox = 2 nm, grown either thermally or by plasma-enhanced atomic layer deposition, carrier transport is pinhole-dominant for Tann = 1050 degrees C, whereas no electric current through the SiOx layer could be detected for lower Tann. Remarkably, the dominant transport mechanism is not affected by the substrate surface morphology, although lower values of rho c were measured on textured wafers compared to planar surfaces. Lifetime measurements suggest that the best carrier selectivity can be achieved by choosing Tann right above the transition range, but not too high, in order to induce pinhole dominant transport while preserving a good passivation quality.

The potential of passivating contacts incorporating in situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films grown by low pressure chemical vapor deposition (LPCVD) is demonstrated in this work by integrating these layers at the rear side of large-area (241.3 cm(2)) bifacial n-type Tunnel Oxide Passivated Contact (nTOPCon) solar cells with diffused front emitter and screen-printed contacts. In situ doped poly-Si films are studied as their use could simplify the production of industrial n-TOPCon solar cells compared to the common approach relying on ex situ doping of intrinsic LPCVD poly-Si films. The developed poly-Si passivating contacts exhibited excellent characteristics with low recombination current densities in passivated and screen-printing metallized regions down to 2.3 fA/cm(2) and 65.8 fA/cm(2), respectively, and a low contact resistivity of 2.0 m Omega.cm(2). For reaching the best passivating contact characteristics and high solar cell efficiencies, a poly-Si film thickness of 150-200 nm was found to be optimal while a polished rear surface morphology was found to be beneficial. The best solar cell reached a certified power conversion efficiency of 23.01% along with a high open circuit voltage of 691.7 mV, enabled by the passivating contacts with the in situ doped poly-Si films. 1-cell glass-glass laminates were also fabricated with the developed solar cells, which showed no loss in their power output both upon 400 thermal cycles and after 1000 h of damp heat testing. Lastly, a roadmap is presented, indicating strategies to achieve efficiencies up to 25.5% with n-TOPCon solar cells incorporating the in situ P-doped LPCVD poly-Si films.

Contactless plating with electroless solutions can provide self-aligned high-efficiency contacts with very low silver content, using simple and inexpensive equipment. With prior surface activation, it can even be used to metallize both sides of bifacial silicon solar cells simultaneously. However, we observe in such a coplating process with nickel, where surface activation is achieved by immersion plating and thickening by electroless plating, that V oc and fill factor can sometimes significantly decrease with immersion-plating time. To understand the reason for this electrical degradation, we studied the impact of immersion plating on the microstructure of the plated silicon surface. The evolution of the Si-Ni interface was studied by scanning and transmission electron microscopies, energy-dispersive X-ray analysis, secondary ion mass spectrometry, and scanning spreading resistance microscopy. Our attention focused on metal in-diffusion, silicon roughening and etching as the origin for increased recombination. Etching was found to have a significant impact on V oc . The thickness of N + Si etched during Ni deposition can in fact suppress in a few locations most of the field-effect passivation underneath the contacts. This means that a thicker surface field with doping beyond 10 19 /cm 3 must be foreseen under the plated areas, or that the amount of Si lost in the reaction must be reduced. Our observations also confirm that immersion plating can hinder silicide formation and allow Ni in-diffusion, which may be a concern for reliability.

Nowadays, material manufacturers are engineering module materials to optimize the energy production of the PV modules. One of the elements which can be influenced is the optical scattering of a material. In this study, we quantified the effect of a scattering front encapsulant on the energy production of PV modules. First, a wavelength-dependent scattering model was developed in the ray-tracing software PVlighthouse. This model was used to find the optimal scattering conditions, looking at the photo-generated current for a glass-glass PV module with flat front surface. It was shown that a gain of +0.63 mA/cm2 can be obtained for optimal scattering conditions. The scattering is mostly beneficial when the light strikes the module surface at a perpendicular angle. The outcome of the optimization study was implemented in IMEC’s energy yield simulation framework. This framework was used to estimate the energy gain of PV module with scattering front encapsulant when installed in Kuwait’s desert. It was shown that an energy production gain of 1.8% can be expected in case of a glass-glass module with flat front surface and ARC coating.

Nowadays, material manufacturers are engineering module materials to optimize the energy production of the PV modules. One of the elements which can be influenced is the optical scattering of a material. In this study, we quantified the effect of a scattering front encapsulant on the energy production of PV modules. First, a wavelength-dependent scattering model was developed in the ray-tracing software PVlighthouse. This model was used to find the optimal scattering conditions, looking at the photo-generated current for a glass-glass PV module with flat front surface. It was shown that a gain of +0.63 mA/cm2 can be obtained for optimal scattering conditions. The scattering is mostly beneficial when the light strikes the module surface at a perpendicular angle. The outcome of the optimization study was implemented in IMEC’s energy yield simulation framework. This framework was used to estimate the energy gain of PV module with scattering front encapsulant when installed in Kuwait’s desert. It was shown that an energy production gain of 1.8% can be expected in case of a glass-glass module with flat front surface and ARC coating.

The current work is aimed at the development of the building blocks for the integration of polysilicon-based passivating contacts in co-plated n-PERT front junction solar cells. We show that both n-type poly and p-type poly layers (called n-poly and p-poly hereafter) can be obtained simultaneously by the sintering of undoped (i-poly) layers during the POCI 3 diffusion that induces the auto-doping from an existing B-doped emitter. State of the art J 0 values with very high uniformity were measured for n-poly, auto doped p-poly, and boron emitter. The total area weighted J 0 of a passivated cell before metallization is calculated to be around 32 fA/cm 2 . We also show the viability of a laser oxidation process to pattern the front p-poly Si layer without measurable damage. Finally, we demonstrate laser ablation and plating processes that induce only very limited damage, leading to a high iV oc of around 700 mV for asymmetric samples with p and n-poly passivated surfaces.

The potential of in situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films by low pressure chemical vapor deposition (LPCVD) was studied for the realization of poly-Si/SiO x passivating contacts. In situ doping of poly-Si, as an alternative to ex situ methods, could enable simpler fabrication of industrial solar cells featuring these passivating contacts. With this approach, recombination current densities down to 1.7 fA/cm 2 and 3.5 fA/cm 2 were achieved on saw-damage removed and textured Cz-Si surfaces, respectively. It was found that the use of thermal SiO x , high active doping in the poly-Si, and hydrogenation improve the passivation quality. In addition, while post-LPCVD annealing was also beneficial, dopant loss from poly-Si at high annealing thermal budgets was observed to be detrimental to the specific contact resistivity and passivation quality, thus making it crucial to mitigate such dopant losses.

Passivating contacts consisting of polycrystalline silicon (poly-Si) and thin silicon-oxide (SiOx) layers facilitate a significant reduction of recombination losses in silicon solar cells. Nevertheless, these gains come with short circuit current density (J(sc)) losses due to parasitic absorption by the poly-Si. Even if the passivating contacts are employed at the rear side only, absorption, particularly due to free carriers (FCA) in the heavily doped poly-Si, may still lead to significant J(sc) losses. In this work, these losses are characterized as a function of the poly-Si thickness (t(poly)) by the analysis of front reflectance spectra in the infrared (IR). For this study, two sets of samples with different n-type full-area poly-Si passivating contacts at the rear are compared to references with a phosphorus(P)-diffused back surface field (BSF) instead. For the two sets, J(sc) losses with respect to the references (Delta J(sc)) are 0.10 mA/cm(2) and 0.42 mA/cm(2) per 100 nm thick poly-Si, respectively. The difference between the two values is studied by Hall measurements and interpreted to be due to the over three times as high free carrier concentration (N-D,N-act) in the poly-Si layers of the second set of samples as the first set. On the other hand, lifetime measurements showed an excellent passivation yielding an implied open circuit voltage (iV(oc)) up to 736 mV only for the samples with the more heavily doped poly-Si, whereas iV(oc) of 683 mV was measured for the first set, which indicates a trade-off between absorption losses and passivation quality.