Photovoltaic modules are typically not optimized for conditions of partial shading. One proposed approach to improve their shade tolerance is to implement maximum power point tracking on different strings of cells within the modules. However, this approach increases the demand for sub-module power converters, which poses a challenge. To address this, researchers have suggested integrating power electronic components directly into the module laminate, or even within the solar cells themselves. Despite these advancements, limited research has focused on integrating the most bulky component: the inductor. This study investigates through simulations whether planar air-core inductors can yield the required properties to support sub-module power conversion. The simulated inductors have an area that is as large as an industrial crystalline silicon solar cell. First, it is shown how the interplay between the different design parameters, such as track spacing, track width, number of turns, and middle gap size, plays an important role in the inductor properties at high frequency. The coil geometries that are simulated yield inductance values between 0.3 μH and 3.2 μH. Subsequently, the feasibility of implementing these inductors into an exemplary DC–DC boost converter is evaluated. To adequately reduce the ripple current, a significant switching frequency of at least several hundred kHz is required. Additionally, at 500 kHz, an inductor thickness of around 0.5 mm is necessary to keep the ohmic losses in the inductor below 2% of the total generated power in standard test conditions. While demonstrating feasible combinations, these findings also present significant challenges.@en

A thorough understanding of the small-signal response of solar cells can reveal intrinsic device characteristics and pave the way for innovations. This study investigates the impedance of crystalline silicon PN junction devices using TCAD simulations, focusing on the impact of frequency, bias voltage, and the presence of a low–high (LH) junction. It is shown that the PN junction exhibits the behavior of a parallel resistor–capacitor circuit (RC-loop) with fixed element values at low frequencies, but undergoes relaxation in both resistance R_j and capacitance C_j as frequency increases. Moreover, it is revealed that the addition of a LH junction impacts the impedance by altering R_j, C_j, and the series resistance R_s. Finally, while various publications on solar-cell impedance model the LH junction using an RC-loop, the findings in this study indicate that such a model does not accurately represent the underlying physics. Instead, this approach is likely compensating for the frequency-dependent behavior of R_j and C_j.

@en

Polycrystalline silicon (poly-Si) carrier-selective passivating contacts (CSPCs), featuring high photoconversion efficiency (PCE) and cost-effectiveness, have emerged as a promising approach for high-efficiency crystalline silicon (c-Si) solar cells. To minimize parasitic absorption losses induced by doped poly-Si window layers, wide bandgap oxygen-alloyed poly-Si (poly-SiO_x) layers are developed. However, challenges persist in achieving excellent surface passivation for boron-doped poly-SiO_x contact stacks, likely caused by boron diffusion during annealing and the reduced doping concentration resulting from lower crystallinity as oxygen content increases. In this study, we investigate the impact on the passivating contact structure and solar cell performance of a 10-nm thick intrinsic hydrogenated amorphous silicon buffer layer with varying oxygen content (a-Si (O_x):H) deposited by plasma-enhanced chemical vapor deposition (PECVD), and placed between the tunneling silicon oxide (SiO_x) and the poly-SiO_x (p⁺). After the hydrogenation step, we obtain both high passivation quality with implied open circuit voltage (iV_oc) of 728.3 mV and low contact resistivity (ρ_c) of 59.18 mΩ cm² on polished surface for oxygen-free a-Si:H buffer layer. These improvements can be attributed to the appropriate thickness of the tunnel oxide and confirmed by transmission electron microscopy (TEM) images, to higher crystallinity of the buffer layer, which facilitates more efficient doping in the buffer layer. This is evidenced by energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) results. At the device level, a front-side textured, rear-side flat, rear junction poly-SiO_x/poly-SiO_x solar cell on n-type c-Si wafer, an efficiency improvement can be observed from 3.55 % without a PECVD buffer layer to 18.9 % with an oxygen-free a-Si:H PECVD buffer layer. The impact of the buffer layer crystallinity on cell performance is further demonstrated by deploying a 10-nm thick LPCVD buffer layer, which facilitates an efficiency of 21.15 % for the same device structure.

@en

In this work, we optimize cerium-doped indium oxide – ICO – thin films with respect to sputtering parameters such as oxygen flow, deposition pressure, applied RF power. Optimized 35-nm-thick ICO layer demonstrated a mobility of 44.22 cm²/Vs, a carrier concentration of 1.65 × 10²⁰/cm³, and a resistivity of 8.56 × 10⁻⁴ Ω cm. Application of such layers into front/back contact silicon heterojunction (FBC-SHJ) solar cells enhanced the short-circuit current density (J_SC) by 0.67 when compared to SHJ cell endowed with tin-doped indium oxide (ITO), respectively. This enhancement yielded an absolute power conversion efficiency (PCE) improvement of 0.55 %, reaching efficiencies of around 23.6 % for devices with ICO layers.

@en

The impedance of solar cells can be leveraged for a variety of innovative applications. However, for the continued advancement of such applications, it is crucial to understand how the impedance varies during practical operation. This work characterizes the impedance of modern crystalline silicon solar cells across different bias voltages and under varying illumination and temperature conditions. It is found that for a given bias voltage, variations in temperature have a notably stronger impact on PN junction impedance than changes in irradiance. However, during maximum power point (MPP) tracking, variations in irradiance have a larger influence on the PN junction impedance than temperature variations. This is related to the shifting operating voltage during operation. Furthermore, it is shown that the capacitance during practical operation can strongly vary for different solar cells. For instance, the areal MPP capacitance values of the two cells tested in this study at 0.1 sun irradiance and a temperature of 30 °C were 0.283 μF/cm2 and 20.2 μF/cm2, a 71-fold difference. Conversely, the range of the MPP diffusion resistance was found to be highly similar for different cells. The results of this study enhance the understanding of solar-cell impedance and have a broad applicability.@en

Positive Energy Districts (PEDs) are integral to achieving sustainable urban development by enhancing energy self-sufficiency and reducing carbon emissions. This paper explores energy balance calculations in four diverse case study districts within different climatic conditions—Fiat Village in Settimo Torinese (Italy), Großschönau (Austria), Beursplain in Amsterdam (Netherlands), and Lunca Pomostului in Reşiţa (Romania)—as part of the SIMPLY Positive project. Each district faces unique challenges, such as outdated infrastructure or heritage protection, which we address through tailored strategies including building renovations and the integration of renewable energy systems. Additionally, we employ advanced simulation methodologies to assess energy performance. Simulation results highlight the significance of innovative technologies like photovoltaic-thermal (PVT) systems, application of demand-side actions, and flexible grid usage. Furthermore, mobility assessments and resident-driven initiatives demonstrate the critical role of community engagement in reducing carbon footprints. This study underscores the adaptability of PED frameworks across varied urban contexts and provides actionable insights for scaling similar strategies globally, supporting net-zero energy targets.@en

At standard test conditions (STC), the performance of photovoltaic modules is compared using efficiency. As irradiance and module temperature fluctuate over the year and STC efficiency does not assess the performance of the module accurately in real world conditions, the annual energy yield is used instead as performance metric. Perovskite/silicon tandem solar cells are being massively researched and sought after in PV industry for their efficiency well above 34% with further growth perspective. In this work, to evaluate and compare performance of different perovskite/silicon tandem photovoltaic (PV) modules based on different bottom cell technologies, we use a hybrid modelling approach. Such approach, combining experimentally obtained and simulated current-voltage curves, flexibly predicts the annual energy yield of novel tandem PV modules via our PVMD toolbox and enables their optimization in any location. In particular, considering (i) mono- and bi-facial architectures, (ii) 2-terminal and 4-terminal module configurations, and (iii) silicon heterojunction or novel poly-SiOx passivated c-Si solar bottom cells, we compare the annual energy yield of different perovskite/silicon tandem modules and we optimize their performance in different locations with respect to different perovskite thickness and bandgaps@en

Reducing indium consumption in transparent conductive oxide (TCO) layers is crucial for mass production of silicon heterojunction (SHJ) solar cells. In this contribution, optical simulation-assisted design and optimization of SHJ solar cells featuring MoO_x hole collectors with ultra-thin TCO layers is performed. Firstly, bifacial SHJ solar cells with MoO_x as the hole transport layer (HTL) and three types of n-contact as electron transport layer (ETL) are fabricated with 50 nm thick ITO on both sides. It is found that bilayer (nc-Si:H/a-Si:H) and trilayer (nc-SiO_x:H/nc-Si:H/a-Si:H) as n-contacts performed electronically and optically better than monolayer (a-Si:H) in bifacial SHJ cells, respectively. Then, as suggested by optical simulations, the same stack of tungsten-doped indium oxide (IWO) and optimized MgF₂ layers are applied on both sides of front/back-contacted SHJ solar cells. Devices endowed with 10 nm thick IWO and bilayer n-contact exhibit a certified efficiency of 21.66% and 20.66% when measured from MoO_x and n-contact side, respectively. Specifically, when illuminating from the MoO_x side, the short-circuit current density and the fill factor remain well above 40 mA cm⁻² and 77%, respectively. Compared to standard front/rear TCO thicknesses (75 nm/150 nm) deployed in monofacial SHJ solar cells, this represents over 90% TCO reduction. As for bifacial cells featuring 50 nm thick IWO layers, a champion device with a bilayer n-contact as ETL is obtained, which exhibits certified conversion efficiency of 23.25% and 22.75% when characterized from the MoO_x side and the n-layer side, respectively, with a bifaciality factor of 0.98. In general, by utilizing a n-type bilayer stack, bifaciality factor is above 0.96 and it can be further enhanced up to 0.99 by switching to a n-type trilayer stack. Again, compared to the aforementioned standard front/rear TCO thicknesses, this translates to a TCO reduction of more than 67%.

@en

This paper presents dynamic air-based models of a hybrid photovoltaic-thermal (PVT) collector. The models are developed with the aim of estimating the temperature of the collector components and therefore of estimating the annual generation of electrical energy and thermal energy outputs, by using actual climate data of six different cities based on Köppen-Geiger-Photovoltaic (KGPV) climate zones. The results show that the unglazed type collector has the best PV cooling while the dual channel collector has the best air heating among air-based PVT collectors. The results also indicate that the use of additional fluid enhances both electrical and thermal performance. The dynamic models are validated by comparison with results found in the literature. The paper also discusses a novel bi-fluid PVT system combined with a storage tank and an H-infinity based robust controller that can handle uncertainties. The results of the bi-fluid system show that the fraction of energy demand covered by the system is highly dependent on climate conditions and the collector's surface area. It was found that for a small-scale house (standard for four people), the proposed system can cover more than 70% annual domestic hot water demand for cities with high solar irradiance and 32% for a city with low solar irradiance.

@en

This work presents a practical approach to designing an optical filter for thermal management for photovoltaic modules. The approach emphasizes the practicality of manufacturing over optical performance. Simulation work demonstrates that, for an interdigitated back contact solar cell architecture, complete rejection of infrared radiation offers limited thermal benefits requiring highly complex optical filter designs. An alternative approach consists of reducing thermalization losses by providing reflectance at lower wavelength values. An optical filter design that fulfills this requirement is possible using simple structures based on two materials and taking advantage of the harmonics present in quarter wavelength optical thickness designs. The filter is later optimized for angular performance via second-order algorithms, resulting in a device consisting of only 15 thin-film layers. Performance simulations on two locations, Delft (the Netherlands) and Singapore, estimate a temperature reduction of 2.20°C and 2.45°C, respectively. In a single year, the optical loss produced by the filter is not compensated via temperature reduction. However, improvements in the annual degradation rate show that in Singapore, the overall effect of the filter on the lifetime DC energy yield is positive.

@en

Nowadays, an increasing share of photovoltaic (PV) systems makes use of module- or submodule-level power electronics (PE). Furthermore, PE is used in stand-alone devices powered by PV-storage solutions. One way to facilitate further implementation of PE in PV applications is to integrate PE components into crystalline silicon PV cells. Herein, the COSMOS device is introduced, denoting COmbined Solar cell and metal-oxide-semiconductor field-effect transistor (MOSFET). Specifically, the combined manufacturing of lateral power MOSFETs and interdigitated back contact solar cells with tunnel-oxide passivated contacts (TOPCon) on a single wafer is reported. Many steps of the proposed process flow are used for the fabrication of both devices, enabling cost-effective integration of the MOSFET. Both n-type solar cells with integrated p-channel MOSFETs (PMOS) and p-type solar cells with integrated n-channel MOSFETs (NMOS) are successfully manufactured. NMOS devices perform better in achieving low on-resistance, while PMOS devices exhibit lower leakage currents. Furthermore, the study reveals integration challenges where off-state leakage currents of the MOSFET can increase due to illumination and specific configurations of monolithic interconnections between the MOSFET and the solar cell. Nevertheless, for both n-type and p-type solar cells, efficiencies exceeding 20% are achieved, highlighting the potential of the proposed process for COSMOS devices.

@en

Transition metal oxide (TMO) thin films exhibit large bandgap and hold great potential for enhancing the performance of silicon heterojunction (SHJ) solar cells by increasing the short-circuit current density significantly. On the other hand, achieving precise control over the electrical properties of TMO layers is crucial for optimizing their function as efficient carrier-selective layer. This study demonstrates a general and feasible approach for manipulating the quality of several TMO films, aimed at enhancing their applicability in silicon heterojunction (SHJ) solar cells. The core of our method involves precise engineering of the interface between the TMO film and the underlying hydrogenated intrinsic amorphous silicon passivation layer by managing the reaction of the TMO on the surface. X-ray photoelectron spectroscopy spectra demonstrate that our methods can modify the oxygen content in TMO films, thereby adjusting their electronic properties. By applying this method, we have successfully fabricated WO_x-based SHJ solar cells with 23.30 % conversion efficiency and V₂O_x-based SHJ solar cells with 22.04 % conversion efficiency, while keeping n-type silicon-based electron-transport layer at the rear side. This research paves the way for extending such interface engineering methods to other TMO materials used as hole-transport layers in SHJ solar cells.

@en

This work is a long-term, interannual, and experimental study conducted in multiple locations. It studies the effects of phase change materials (PCMs) on photovoltaic modules’ performance by reducing their operational temperature. Two PV modules were manufactured so that PCM slabs could be mechanically attached to their backside, ensuring contact with the related photovoltaic active area. Experiments were conducted in Delft, Netherlands, from 2019 until 2021 and in Catania, Italy, during the winter and start of spring of 2023. The experiment also considered two installation layouts: building integrated (Delft) and standard rack-mounted (Catania). The measurements showed that the PCM provides significant cooling under both locations, with a temperature reduction of up to 15 °C. In Delft, thermal control could be obtained for most of the sunny hours of the day, even during the summer months. In Catania, the module with PCM presented, on occasion, higher temperatures than its standard counterpart, primarily due to winter-time environmental conditions. However, the PCM provided sufficient thermal control on all conditions, ensuring increased energy yield. This increase ranged from 2.1 to 2.5 % in Delft and 1.3–1.6 % in Italy.

@en

Solar photovoltaic (PV) energy is variable. The output power can change considerably in a matter of minutes, imposing challenges on the control of systems connected downstream. The power from these systems can be smoothed using electric storage, potentially increasing the system cost. An alternative is to deliberately curtail the power before it starts to change. This strategy relies on ultra-short-term forecasting to determine the curtailment point. Unfortunately, forecasting is prone to errors and high uncertainty even in the very short-term, leading to control errors. We propose an active power curtailment control strategy for a stand-alone solar photovoltaic system powering an electrolyzer. Our work's novelty relies on the controller's ability to deal with large forecasting errors and high uncertainty, combining artificial intelligence for predicting the power ramps and fuzzy logic to account for imperfect prediction. We validated our approach using a hardware emulator of the photovoltaic system, power converter and electrolyzer. Under clear sky conditions, the curtailment results in unnecessary energy loss, while under variable irradiance, the controller successfully smooths the power ramps within 10% of the PV system's nominal power. Although our approach was designed for a stand-alone system, its concept can be directly applied to grid-connected systems as well.

@en

Clouds moving in front or away from the sun are the leading cause of irradiance variability. These variations have a repercussion on the electricity production of photovoltaic systems. Predicting such changes is essential for proper control of these systems and for maintaining grid stability. Images from the sky have proven to help with short-term solar irradiance forecasting, especially when combined with artificial intelligence. Nevertheless, these models tend to smooth the irradiance fluctuations. We propose a forecasting model to predict the clear-sky index in a forecast horizon of 20 min with a 1-minute resolution. Our model, based on a classifier to determine the sky conditions and, on an optical flow, applies an artificial intelligence model explicitly trained on each class of sky conditions. This strategy has an equivalent performance to an unclassified model and a forecast skill between 5 and 20% with respect to the smart persistence model for most classes of sky conditions while requiring considerably less training data. Although our model reduces the overall predicting error, it still has difficulties predicting irradiance changes and mainly overcast days. Our classifying strategy can be applied to other models targeting different objectives to predict sudden changes in either irradiance or power related to photovoltaic systems.

@en

Single junction crystalline silicon (c-Si) solar cells are reaching their practical efficiency limit whereas perovskite/c-Si tandem solar cells have achieved efficiencies above the theoretical limit of single junction c-Si solar cells. Next to low-thermal budget silicon heterojunction architecture, high-thermal budget carrier-selective passivating contacts (CSPCs) based on polycrystalline-SiO_x (poly-SiO_x) also constitute a promising architecture for high efficiency perovskite/c-Si tandem solar cells. In this work, we present the development of c-Si bottom cells based on high temperature poly-SiO_x CSPCs and demonstrate novel high efficiency four-terminal (4T) and two-terminal (2T) perovskite/c-Si tandem solar cells. First, we tuned the ultra-thin, thermally grown SiO_x. Then we optimized the passivation properties of p-type and n-type doped poly-SiO_x CSPCs. Here, we have optimized the p-type doped poly-SiO_x CSPC on textured interfaces via a two-step annealing process. Finally, we integrated such bottom solar cells in both 4T and 2T tandems, achieving 28.1% and 23.2% conversion efficiency, respectively.

@en

In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigitated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be “repassivated” after cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L&C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 °C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.@en

To achieve a high performance in sub-module power conditioning circuits, it is important that power converters are designed in accordance with the photovoltaic (PV) cell impedance at the input. Taking this one step further, exploiting the impedance of cell strings could even support novel power conditioning approaches in PV modules. In this work, we characterize the impedance of eight single-cell laminates based on different industrial c-Si PV cell architectures. This characterization is carried out by impedance spectroscopy in dark conditions at room temperature, and the capacitive and inductive effects are evaluated through equivalent model fitting. By comparing the results for the different laminates, it is revealed how the cell design affects its impedance. Our experiments show that the PN junction capacitance at maximum power point varies for the different cells between 0.30 and 45.6 μF/cm². The two main factors contributing to a high PV cell capacitance at maximum power point are (i) a low wafer dopant concentration and (ii) a high maximum power point voltage. In high-efficiency c-Si PV cells that will be fabricated in the coming years, increasing capacitances are expected for operation near the maximum power point. Furthermore, the single-cell laminates exhibit inductances between 63 and 130 nH, and our results indicate that the inductance is mostly affected by the number of busbars and the geometry of the metal contacts.

@en

Silicon heterojunction (SHJ) solar cells have achieved a record efficiency of 26.81% in a front/back-contacted (FBC) configuration. Moreover, thanks to their advantageous high V_OC and good infrared response, SHJ solar cells can be further combined with wide bandgap perovskite cells forming tandem devices to enable efficiencies well above 33%. In this study, we present strategies to realize high-efficiency SHJ solar cells through combined theoretical and experimental studies, starting from the optimization of Si-based thin-film layers to the implementation of electrodes with reduced indium and silver usage. Advanced opto-electrical simulations, which enable comprehensive theoretical understandings of the main physical mechanisms governing carriers’ collection and light management, provide clear pathways for device designs and experimental optimizations. We present the fabricated FBC-SHJ solar cells in both monofacial and bifacial configurations with the best efficiencies of 24.18% and 23.25%, respectively. We point out that to achieve optimum device performance, the compositional materials should be holistically optimized and evaluated as part of the contact stacks with adjacent layers. As an outlook beyond the classical FBC-SHJ solar cell architecture, we propose various novel SHJ-based solar cell architectures. Their potential performance was assessed and compared via rigorous opto-electrical simulations and a maximal efficiency of 27.60% was simulated for FBC-SHJ solar cells featuring localized contacts.

@en

Monolithic perovskite/c-Si tandem solar cells have attracted enormous research attention and have achieved efficiencies above 30%. This work describes the development of monolithic tandem solar cells based on silicon heterojunction (SHJ) bottom- and perovskite top-cells and highlights light management techniques assisted by optical simulation. We first engineered (i)a-Si:H passivating layers for (100)-oriented flat c-Si surfaces and combined them with various (n)a-Si:H, (n)nc-Si:H, and (n)nc-SiOx:H interfacial layers for SHJ bottom-cells. In a symmetrical configuration, a long minority carrier lifetime of 16.9 ms was achieved when combining (i)a-Si:H bilayers with (n)nc-Si:H (extracted at the minority carrier density of 1015 cm-3). The perovskite sub-cell uses a photostable mixed-halide composition and surface passivation strategies to minimize energetic losses at charge-transport interfaces. This allows tandem efficiencies above 23% (a maximum of 24.6%) to be achieved using all three types of (n)-layers. Observations from experimentally prepared devices and optical simulations indicate that both (n)nc-SiOx:H and (n)nc-Si:H are promising for use in high-efficiency tandem solar cells. This is possible due to minimized reflection at the interfaces between the perovskite and SHJ sub-cells by optimized interference effects, demonstrating the applicability of such light management techniques to various tandem structures.

@en