Two terminal (2T) perovskite/copper-indium-gallium-selenide (CIGS) tandem solar cells combine high conversion efficiency with lightweight flexible substrates which can decrease manufacturing and installation costs. In order to improve the power conversion efficiency of these tandem solar cells, the use of advanced simulation tools is crucial to estimate the loss mechanisms. In this regard, most of the available simulation works on tandem solar cells are oriented to minimize optical losses and assuming simplifications for the electrical simulations in particular in the top and bottom cell interconnection at the so-called tunnel recombination junction (TRJ) neglecting the inner physics of the complete tandem device. Therefore, the effect of charge exchange mechanism between top and bottom soler cells on the external parameters of a tandem devices is not fully understood yet. In this work, we present an experimentally validated opto-electrical model based on the fundamental semiconductor equations for the study of loss mechanisms of a reference perovskite/CIGS solar cell. Different from other numerical works, because our simulation platform includes the fundamental working mechanisms of the layers comprising the TRJ, we can properly calculate the losses related to it. We firstly present the calibration and validation of our opto-electrical model with respect to three fabricated reference solar cells: top cell only, bottom cell only and tandem device. Then, we use the calibrated model to evaluate main loss mechanisms affecting the baseline tandem device. Finally, we use the model to propose a roadmap for the optimization of monolithic perovskite/CIGS tandem solar cells.

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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.

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Our study focuses on the optimization of front contact design by exploring a novel bilayer configuration that employs transparent conductive oxides (TCOs) to enhance the efficiency of thin-film silicon solar cells. The TCOs investigated include sputtered hydrogenated indium oxide (IOH), cerium-doped indium oxide (ICO), cerium and hydrogen co-doped indium oxide (ICOH), and intrinsic zinc oxide (i-ZnO). We highlight the suitability of these TCOs in a bilayer design, first analyzing their opto-electrical properties as monolayers and subsequently in bilayer configurations. The IOH/i-ZnO bilayer architecture, in particular, demonstrates promising opto-electrical properties on both flat glass and micro-textured glass substrates. IOH/i-ZnO on flat glass substrate demonstrates remarkable mobility (143.44 cm²/Vs) and a carrier concentration in the order of 10¹⁹cm^-3. The mean of reflectance (R) trends consistently exceeds 80%, while the mean of transmittance (T) trends falls below 20% beyond 500 nm. The interference effects within the bilayers are minimized for designs on micro-textured glass, preserving values within a desirable range. These findings represent an innovative approach to front contact design for thin-film silicon solar cells, emphasizing the potential of bilayer configurations to advance solar cell technology.

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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.

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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.

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The photovoltaic (PV) module energy rating standard series IEC 61853 does not cover bifacial PV modules. However, the market share of bifacial PV modules has dramatically increased in recent years and is projected to grow. This work demonstrates how Parts 3 and 4 of the IEC 61853 standard could be extended to bifacial modules. First, we develop an irradiance model that uses the data already given in the standard IEC 61853-4 to calculate the irradiance on the rear side of the module. Second, we propose a way to extend the energy yield calculation algorithm IEC 61853-3 to include bifacial modules and make it available to the PV community. This rear irradiance and bifacial energy yield calculation procedure is tested using real outdoor measurements for a nine-month period with a root mean square difference between measured and simulated energy yield of 4.65%. To conclude, we investigate the impact of different climates and normalization on the bifacial module energy rating results.

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The tandem PV technology can potentially increase the efficiency of PV modules over 30%. To design efficient modules, a quantification of the different losses is important. Herein, a model for quantifying the energy loss mechanisms in PV systems under real-world operating conditions with a level of detail back to the components and their fundamental properties is presented. Totally, 17 losses are defined and divided into four categories (fundamental, optical, electrical, and system losses). As example, a system based on a > 29% two-terminal perovskite/silicon tandem cell is considered. The loss distribution at standard test conditions is compared to four geographical locations. The results show that the thermalization, reflection, and inverter losses increase by 1.2%, 1.1%, and 1.4%, respectively, when operating outdoors. Additionally, it is quantified how fill factor gains partly compensate the current mismatch losses. For example, a mismatch of 7.0% in photocurrent leads to a power mismatch of 1.2%. Therefore, the power mismatch should be used as indicator for mismatch losses instead of a current mismatch. Finally, herein, it is shown that solar tracking increases not only the in-plane irradiance but also the efficiency of the tandem module.

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We investigate gentle front side textures for perovskite/silicon tandem solar cells. These textures enhance the absorption of sunlight, yet are sufficiently gentle to allow deposition of an efficient perovskite top cell. We present a tandem solar cell with such gentle texture, fabricated by Kaneka corporation, with an efficiency as high as 28.6%. We perform an extensive ray-optics study, exploring non-conformal textures at the front and rear side of the perovskite layer. Our results reveal that a gentle texture with steepness of only 23° can be more optically efficient than conventional textures with more than double that steepness. We also show that the observed anti-reflective effect of such gentle textures is not based a double bounce, but on light trapping by total internal reflection. As a result, the optical effects of the encapsulation layers play an important role, and have to be accounted for when evaluating the texture design for perovskite/silicon tandems.

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Reducing indium consumption, which is related to the transparent conductive oxide (TCO) use, is a key challenge for scaling up silicon heterojunction (SHJ) solar cell technology to terawatt level. In this work, we developed bifacial SHJ solar cells with reduced TCO thickness. We present three types of In₂O₃-based TCOs, tin-, fluorine-, and tungsten-doped In₂O₃ (ITO, IFO, and IWO), whose thickness has been optimally minimized. These are promising TCOs, respectively, from post-transition metal doping, anionic doping, and transition metal doping and exhibit different opto-electrical properties. We performed optical simulations and electrical investigations with varied TCO thicknesses. The results indicate that (i) reducing TCO thickness could yield larger current in both monofacial and bifacial SHJ devices; (ii) our IWO and IFO are favorable for n-contact and p-contact, respectively; and (iii) our ITO could serve well for both n-contact and p-contact. Interestingly, for the p-contact, with the ITO thickness reducing from 75 nm to 25 nm, the average contact resistivity values show a decreasing trend from 390 mΩ cm² to 114 mΩ cm². With applying 25-nm-thick front IWO in n-contact, and 25-nm-thick rear ITO use in p-contact, we obtained front side efficiencies above 22% in bifacial SHJ solar cells. This represents a 67% TCO reduction with respect to a reference bifacial solar cell with 75-nm-thick TCO on both sides.

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The current climate and energy crisis urgently needs solar cells with efficiencies above the 29% single junction efficiency bottleneck. Silicon/perovskite tandem solar cells are a solution, which is attracting much attention. While silicon/perovskite tandem cells in 2-terminal and 4-terminal configurations are well documented, the three-terminal concept is still in its infancy. It has significant advantages under low light intensities as opposed to concentrated sunlight, which is the critical factor in designing tandem solar cells for low-cost terrestrial applications. This study presents novel studies of the sub-cell performance of the first three-terminal perovskite/silicon selective band offset barrier tandem solar cells fabricated in an ongoing research project. This study focuses on short circuit current and operating voltages of the sub-cells under light intensities of one sun and below. Lifetime studies show that the perovskite bulk carrier lifetime is insensitive to illumination, while the silicon cell's lifetime decreases with decreasing light intensity. The combination of perovskite and silicon in the 3T perovskite-silicon tandem therefore reduces the sensitivity of VOC to light intensity and maintains a relatively higher VOC down to low light intensities, whereas silicon single-junction cells show a marked decrease. This technological advantage is proposed as a novel advantage of three-terminal perovkite/silicon solar cells for low light intensities of one sun or less.@en

When integrated into urban environments, photovoltaic (PV) systems usually present operational temperatures that are significantly higher than those shown by rack-mounted systems. High operating temperatures are associated with reduced reliability of PV modules and significantly impact the electrical performance of solar cells. Utilizing the heat produced on PV modules or reducing operating temperatures can bolster their application within the building sector. We present the three main concepts studied to achieve these goals. First, a PV is a chimney concept that allows the use of the heat generated by the modules. Simulations for a PV chimney installed on a building in the Netherlands showed that although the heat quality produced inside its cavity was low, the potential use of the air mass flow for ventilation applications is promising. Additionally, we present two passive cooling solutions that can reduce the operating temperatures of PV modules: Optical filters and phase change materials. Experimental measurements in Delft showed that these solutions reduce the operating temperature of PV modules between 4 °C to 20 °C, particularly under high irradiance hours.

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We introduce a novel simulation tool capable of calculating the energy yield of a PV system based on its fundamental material properties and using self-consistent models. Thus, our simulation model can operate without measurements of a PV device. It combines wave and ray optics and a dedicated semiconductor simulation to model the optoelectronic PV device properties resulting in the IV-curve. The system surroundings are described via spectrally resolved ray tracing resulting in a cell resolved irradiance distribution, and via the fluid dynamics-based thermal model, in the individual cell temperatures. A lumped-element model is used to calculate the IV-curves of each solar cell for every hour of the year. These are combined factoring in the interconnection to obtain the PV module IV-curves, which connect to the inverter for calculating the AC energy yield. In our case study, we compare two types of 2 terminal perovskite/silicon tandem modules with STC PV module efficiencies of 27.7% and 28.6% with a reference c-Si module with STC PV module efficiency of 20.9%. In four different climates, we show that tandem PV modules operate at 1–1.9 °C lower yearly irradiance weighted average temperatures compared to c-Si. We find that the effect of current mismatch is significantly overestimated in pure optical studies, as they do not account for fill factor gains. The specific yields in kWh/kWp of the tandem PV systems are between −2.7% and +0.4% compared to the reference c-Si system in all four simulated climates. Thus, we find that the lab performance of the simulated tandem PV system translates from the laboratory to outdoors comparable to c-Si systems.

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Organic-inorganic metal halide perovskites have attracted a considerable interest in the photovoltaic scientific community demonstrating a rapid and unprecedented increase in conversion efficiency in the last decade. Besides the stunning progress in performance, the understanding of the physical mechanisms and limitations that govern perovskite solar cells are far to be completely unravelled. In this work, we study the origin of their hysteretic behaviour from the standpoint of fundamental semiconductor physics by means of technology computer aided design electrical simulations. Our findings identify that the density of shallow interface defects at the interfaces between perovskite and transport layers plays a key role in hysteresis phenomena. Then, by comparing the defect distributions in both spatial and energetic domains for different bias conditions and using fundamental semiconductor equations, we can identify the driving force of hysteresis in terms of slow recombination processes and charge distributions.@en

Thin films of transition metal oxides such as molybdenum oxide (MoO_x) are attractive for application in silicon heterojunction solar cells for their potential to yield large short-circuit current density. However, full control of electrical properties of thin MoO_x layers must be mastered to obtain an efficient hole collector. Here, we show that the key to control the MoO_x layer quality is the interface between the MoO_x and the hydrogenated intrinsic amorphous silicon passivation layer underneath. By means of ab initio modelling, we demonstrate a dipole at such interface and study its minimization in terms of work function variation to enable high performance hole transport. We apply this knowledge to experimentally tailor the oxygen content in MoO_x by plasma treatments (PTs). PTs act as a barrier to oxygen diffusion/reaction and result in optimal electrical properties of the MoO_x hole collector. With this approach, we can thin down the MoO_x thickness to 1.7 nm and demonstrate short-circuit current density well above 40 mA/cm² and a champion device exhibiting 23.83% conversion efficiency.

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Building Integrated Photovoltaic systems can produce a significant portion of the energy demand of urban areas. Despite their potential, they remain a niche technology that architects and project engineers still find esthetically limited. The dark blue or black color of standard photovoltaic panels is considered inappropriate for restoration projects of historic buildings and represents a major constraint on the development of new projects. This work will provide insight into how the use of optic filters can offer new pathways for architectural acceptance of photovoltaic panels. Optic filters selectively reflect or transmit light by interference and can be designed and fabricated using cost-effective and industrially compatible processes. By using in-house developed ray tracing software coupled with TCAD Sentaurus, more than 400 colors were obtained, and their impact on the opto-electrical performance of interdigitated back-contacted solar cells was studied. Results show a maximum efficiency loss of 1.6% absolute at the perpendicular incidence of light on the range of obtained colors when compared with a standard dark blue solar cell. Simulations for different angles of incidence showed that the current reduction on the standard device could be modeled using a cosine relationship. The colored cells, however, deviated significantly from this relationship. We propose that the angular behavior of any cell (colored or standard) could be simulated by modifying the effective irradiance with scaling factors equal to the ratios of the photogenerated current at any angle with respect to the value at normal incidence. We demonstrate that this approach accurately models the effect of the color filter and allows for an easy transition from a bare cell to an encapsulated one. Due to the spectral effect of the filter, we developed both a spectrally resolved optical model and a two-dimensional finite volume transient thermal model. In case of the optical model, we demonstrate an accuracy in the prediction of the reflectance produced by the color with values of mean bias error (MBE) between 2.0% and 3.9%. As for the thermal model, it was validated by first analyzing a standard model under conditions of nominal operating cell temperature and then comparing its results with published scientific literature. Later, we compare its prediction against 2 weeks of measurements. In both cases the thermal model proves an adequate accuracy, yielding differences below 1.5°C with respect to other scientific works and an MBE value of 0.89°C as well as a root-mean-square error value of 2.10°C for the entire measurement period. With the validated models, we studied the effect of the encapsulation on the color perception. We present two options of color filters. The first one produces relatively low reflectance losses and presents relative annual direct current (DC) energy losses of up to 6.4% for Delft, in the Netherlands, and up to 5.9% for Alice Springs in Australia. However, this first option has very poor color brightness. The second studied filter produces highly saturated bright colors. Improving brightness can increase the annual DC relative losses up to 13.7% and 13.5% for Delft and Alice Springs, respectively. Overall, we demonstrate that colored filters based on multilayer optical stacks are a versatile option for coloring cells that allow a good compromise between esthetics and performance.

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A highly transparent passivating contact (TPC) as front contact for crystalline silicon (c-Si) solar cells could in principle combine high conductivity, excellent surface passivation and high optical transparency. However, the simultaneous optimization of these features remains challenging. Here, we present a TPC consisting of a silicon-oxide tunnel layer followed by two layers of hydrogenated nanocrystalline silicon carbide (nc-SiC:H(n)) deposited at different temperatures and a sputtered indium tin oxide (ITO) layer (c-Si(n)/SiO₂/nc-SiC:H(n)/ITO). While the wide band gap of nc-SiC:H(n) ensures high optical transparency, the double layer design enables good passivation and high conductivity translating into an improved short-circuit current density (40.87 mA cm⁻²), fill factor (80.9%) and efficiency of 23.99 ± 0.29% (certified). Additionally, this contact avoids the need for additional hydrogenation or high-temperature postdeposition annealing steps. We investigate the passivation mechanism and working principle of the TPC and provide a loss analysis based on numerical simulations outlining pathways towards conversion efficiencies of 26%.

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The window layers limit the performance of silicon heterojunction (SHJ) solar cells with front and back contacts. Here, we optimized tungsten-doped indium oxide (IWO) film deposited by radio frequency magnetron sputtering at room temperature. The opto-electrical properties of the IWO were manipulated when deposited on top of thin-film silicon layers. The optimal IWO on glass shows carrier density and mobility of 2.1 × 1020 cm−3 and 34 cm2 V−1s−1, respectively, which were tuned to 2.0 × 1020 cm−3 and 47 cm2 V−1s−1, as well as 1.9 × 1020 cm−3 and 42 cm2 V−1s−1, after treated on i/n/glass and i/p/glass substrates, respectively. Using the more realistic TCO data that were obtained on thin-film silicon stacks, optical simulation indicates a promising visible-to-near-infrared optical response in IWO-based SHJ device structure, which was demonstrated in fabricated devices. Additionally, by adding an additional magnesium fluoride layer on device, the champion IWO-based SHJ device showed an active area cell efficiency of 22.92%, which is an absolute 0.98% efficiency gain compared to the ITO counterpart, mainly due to its current gain of 1.48 mA/cm2.@en

The perovskite solar cell (PSC) is one of the most dramatic inventions in the field of photovoltaics in the last half century. The device has rapidly risen from a few percent to efficiencies of over 24% [1] in little over a decade. This rapid development is due in part to the wide family of perovskite absorber and of electron and hole tranport materials available which yields great flexibility. The flip-side of this profusion of materials is the challenge in establishing achievable performance potential of real devices. This paper therefore presents a study of the perovskite solar cell materials and applies numerical modelling techniques to evaluate the most promising materials combinations and their efficiency potential. The preliminary device structure is a simple three-layer design consisting of hole transport layer, perovskite aborber, and electron transport layer, on a glass substrate in a p-i-n or “inverted” configuration. A range of materials for these layers is compared and contrasted for this polarity. The structure is then generalised to more complex designs featuring protective buffer layers which prevent damage to the perovskite absorber layer, and two dimensional perovkite layers which have been shown to improve perovskite material stability. The realistic efficiency potential of the materials considered is discused in the context of the common radiative efficiency limit. The study concludes by recommending promising materials combinations for high efficiency PSC compatible with cost effective indutrial fabrication method for single juntion and for multijunction device design in the context of H2020 Solar-ERANET project BOBTANDEM [2]. This work contributes to define efficiencies achievable in this materials systems, both for single junction and multijunction devices which are of great societal interet for cost effective renewable power generation. @en

The study of a two-terminal (2T) perovskite/c-Si tandem solar cell requires accurate and concurrent description of photons absorption and tunnelling-mediated charge transport. By analysing current collection across the device heterointerfaces, we investigated the effect of (i) perovskite thickness on the short-circuit current density (Jsc) of the tandem device and (ii) temperature on devices performance. We deployed an advanced opto-electrical modelling framework based on optical sub-models from GenPro4 and on self-consistent fundamental semiconductor equations implemented in TCAD Sentaurus. Using these simulations of perovskite/c-Si tandem solar cells, an in-depth analysis of the physics of current contribution of supporting layers has been carried out. Solving numerically the fundamental equations of semiconductors, we theoretically show for the first time that electron-hole pairs photo-generated in the TRJ can be collected, effectively boosting Jsc values well beyond (photocurrent density) Jph levels. In addition, a temperature-based study of these perovskite/c-Si tandem solar cells has been performed to evaluate the temperature coefficient which is useful for their energy yield simulations.

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Since single junction c-Si solar cells are reaching their practical efficiency limit. Perovskite/c-Si tandem solar cells hold the promise of achieving greater than 30% efficiencies. In this regard, optical simulations can deliver guidelines for reducing the parasitic absorption losses and increasing the photocurrent density of the tandem solar cells. In this work, an optical study of 2, 3 and 4 terminal perovskite/c-Si tandem solar cells with c-Si solar bottom cells passivated by high thermal-budget poly-Si, poly-SiO_x and poly-SiC_x is performed to evaluate their optical performance with respect to the conventional tandem solar cells employing silicon heterojunction bottom cells. The parasitic absorption in these carrier selective passivating contacts has been quantified. It is shown that they enable greater than 20 mA/cm² matched implied photocurrent density in un-encapsulated 2T tandem architecture along with being compatible with high temperature production processes. For studying the performance of such tandem devices in real-world irradiance conditions and for different locations of the world, the effect of solar spectrum and angle of incidence on their optical performance is studied. Passing from mono-facial to bi-facial tandem solar cells, the photocurrent density in the bottom cell can be increased, requiring again optical optimization. Here, we analyse the effect of albedo, perovskite thickness and band gap as well as geographical location on the optical performance of these bi-facial perovskite/c-Si tandem solar cells. Our optical study shows that bi-facial 2T tandems, that also convert light incident from the rear, require radically thicker perovskite layers to match the additional current from the c-Si bottom cell. For typical perovskite bandgap and albedo values, even doubling the perovskite thickness is not sufficient. In this respect, lower bandgap perovskites are very interesting for application not only in bi-facial 2T tandems but also in related 3T and 4T tandems.

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