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The efficiency of crystalline silicon solar cells is reaching its practical limit in R&D as well as in high-volume manufacturing. To further drive down the cost of electricity produced by photovoltaics, increasing the efficiency beyond the limit for single-junction crystalline silicon is strongly desirable. 2-terminal perovskite-silicon tandem solar cells represent an appealing option: they benefit from the installed manufacturing capacity and process maturity of the silicon bottom cell, and achieve the high efficiency potential by adding a thin-film top cell. The first lab results with efficiencies of more than 30% have recently been announced [1]. Naturally, such champion devices are initially produced on small areas of the order of 1 cm2 and to date not all of the fabrication methods used in the laboratory meet the challenge of scaling up to industrial production. In this paper we discuss recent advances in the field, with a focus on potential device designs and manufacturing processes.

Nickel oxide ((Formula presented.)) is a promising hole transport material for perovskite/Si tandem solar cells. Various silicon cell architectures may be used as bottom cells. The polycrystalline (poly-Si) (Formula presented.) tunnel diode is expected to be a high-efficiency interconnection scheme between the two subcells of monolithic tandems in p-i-n configuration with a high thermal budget, excellent passivation properties, and low contact resistivity. However, (Formula presented.) is then interfaced to poly-Si((Formula presented.)) and the chemical integrity of the interface due to the necessity of annealing treatments has to be questioned. For this purpose, the (Formula presented.) /poly-Si contact resistivity for different annealing temperatures is investigated between 100 and 500 °C, and two different (Formula presented.) deposition techniques, namely, wet-chemically applied and sputter-deposited (Formula presented.). The values of more than (Formula presented.) are obtained. The insertion of a nm-thin metallic Ni interlayer is shown to enable a tremendous decrease of the contact resistivity by 2-3 orders of magnitude. The formation of (Formula presented.) is proven by highly resolved (scanning) transmission electron microscopy ((S)TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS). This interfacial engineering approach is expected to provide an effective way of improving the contact properties and integrability of (Formula presented.) into various tandem cell processes.

In two-terminal monolithic perovskite/silicon tandem solar cells, top and bottom cells are interconnected in series. To maximize the current of the entire tandem solar cell, current matching of the two sub-cells is needed. Thus, it is necessary to get access to the individual current of each sub-cell. As it is difficult to measure the absolute external quantum efficiency (EQE) for multijunction solar cells in general and especially if perovskite is involved, in this work, the spectrometric characterization technique enables important insight in the sub-cells’ current limitation. In this method, which has already been applied for III-V multijunction solar cells, current-voltage curves are recorded while the spectrum is systematically varied from a blue-rich to a red-rich spectrum. We apply this technique to perovskite/silicon tandem devices consisting of a silicon heterojunction bottom solar cell and top solar cell in the p-i-n architecture with different perovskite absorbers. In our example, a perovskite absorber with a bandgap of 1.68 eV the top solar cell limits the current, whereas current matching could be reached when using an absorber with a lower bandgap of 1.64 eV. Results from spectrometric characterization are then used to scale the EQEs. We show how optimization strategies for both sub-cells can be systematically derived from these results.

The hybrid evaporation/spin-coating route has been widely used for fabrication of highly efficient fully textured perovskite silicon tandem solar cells and is a promising route for upscaling. Nevertheless, fundamental aspects of the fabrication process such as the kinetics of perovskite crystallization and the influence of the environmental conditions remain uncertain. In this work, we investigate the individual stages of tandem-relevant 1.66 eV bandgap perovskite formation and map the structural evolution from the precursor to the perovskite phase until the degradation phase. We find that the kinetics of these transitions can be tuned by varying the humidity or the temperature during the annealing treatment. Specifically, increasing the relative humidity up to 50% elevates the reaction rate and results in improved perovskite quality. This is directly reflected in the solar cell power conversion efficiency with a 3%abs increment on average. While high annealing temperatures are found to promote large grain size growth and enhanced crystallinity, we observe that above 150 °C the remnant PbI2 precursor compromises film quality. Furthermore, the perovskite formation kinetics is fitted using the Johnson-Mehl-Avrami-Kolmogorov model. The Avrami constant is found in the range 0.66-0.87, indicating a diffusion-controlled one-dimensional growth process with an associated activation energy of 54.49 kJ/mol. Using in situ XRD, this work gives insights on key process parameters to ensure reproducible synthesis of high-quality perovskite films.

Nontoxic, all-inorganic perovskite light absorbers have received a great deal of attention in recent years due to their potential to replace lead-containing perovskite materials in photovoltaics. Herein, the synthesis of the lead-free double perovskite Cs2AgBiBr6 as a powder, obtained via spray-drying, is reported to be capable of paving the way toward large scale production. Upon drying of the atomized precursor solution during spray-drying, the double-perovskite phase forms by in situ crystallization. The product that is obtained from spray-drying is compared to the one that is obtained from the so-called solution cooling method, which is often used for the absorber synthesis before dissolving the double perovskite powder for the thin film deposition. The absorber powder gained from the solution cooling method sets the benchmark for the spray-dried absorber powder. XRD and Raman analyses confirm the phase purity of the double perovskite, whereas UV-Vis spectroscopy confirms the desired bandgap. Furthermore, the absorber powders from both synthesis methods are successfully used to deposit and integrate absorber films in single-junction perovskite solar cells. Besides being introduced as an alternative synthesis route for the preparation of double perovskite absorber as dry powders independently from being applied onto a given substrate, the superior advantages of spray-drying compared to the conventional synthesis of the perovskite absorber via the solution cooling method are outlined: Spray-drying not only enables the synthesis of large amounts of perovskite absorber powders but also discards the usage of precarious solvents like concentrated hydrobromic acid and thus eliminates the need for extensive safety precautions. Hence, spray-drying may help the perovskite technology take the next step toward large-scale production and commercialization.

Evaporated charge extraction layers from organic molecular materials are vital in perovskite-based solar cells. For opto-electronic device optimization their complex refractive indices must be known for the visible and near infrared wavelength regime; however, accurate determination from thin organic films below 50 nm can be challenging. By combining spectrophotometry, variable angle spectroscopic ellipsometry, and X-ray reflectivity with an algorithm that simultaneously fits all available spectra, the complex refractive index of evaporated Spiro-TTB and C60 layers is determined with high accuracy. Based on that, an optical losses analysis for perovskite silicon solar cells shows that 15 nm of Spiro–TTB in the front of a n-i-p device reduces current by only 0.1 mA/cm2, compared to a substantial loss of 0.5 mA/cm2 due to 15 nm of C60 in a p-i-n device. Optical device simulation predicts high optical generation current densities of 19.7 and 20.1 mA/cm2 for the fully-textured, module-integrated p-i-n and n-i-p devices, respectively.

8th World Conference on Photovoltaic Energy Conversion; 354-357, We are working on upscaling of perovskite-silicon tandem solar cells from small lab size areas of several square millimeters to full commercial wafer size. This requires the use of processing techniques that can replace the usual spin coating process employed for small lab size areas. As alternatives for large-area depositions spray coating, inkjet printing and slot-die coating are investigated. For highest specific energy yield under field conditions perovskitesilicon tandem solar cells should be textured on the front side. To ensure conformal coating of the random pyramid textured silicon bottom cell we follow a hybrid process route. In a first step, the inorganic components are thermally evaporated to form a scaffold allowing conformal coating of pyramids of arbitrary size and shape. In a second step, the conversion into perovskite is accomplished by infiltration of the scaffold with organic salt solutions. A thermal anneal completes the conversion into a polycrystalline perovskite layer. In addition to upscaling of the cell area we work on replacing the evaporated silver contact grid by screen printed ultralow temperature silver paste. First results on planar perovskite-silicon tandem solar cells, still fabricated with spin coating processing but with screen-printed front contacts, resulted in a certified stabilized conversion efficiency of 22.5% on 104 cm2 total cell area.

Perovskite-silicon tandem solar cells have shown a rapid progress within the past 5 years in terms of their research cell efficiency and are currently being investigated as candidates for the next generation of industrial PV devices. This raises the question of which silicon bottom cell will be most suitable for tandem application. Currently, the silicon heterojunction (SHJ) technology dominates in tandem research achieving world records. However, it is an open issue of how to transfer these research results to industrial mass production, which is driven by cost reduction and resource efficiency and includes challenges like upscaling and long‐term stability. Therefore, it is highly relevant for the PV industry to get reliable and predictive estimates on the efficiency and cost potential, as well as technologically feasible solutions. In this work, we elaborate on silicon bottom cell concepts based on the PERC, TOPCon, and SHJ technology combined with two different interconnection concepts. For each tandem device, the efficiency potential is investigated by means of an experimentally validated simulation model. Second, we evaluate the bottom cell concepts in terms of all‐in cell costs per piece. Bringing the efficiency potential and cost evaluation together allows us to assess the different tandem cell concepts in terms of all‐in module cost per watt peak. Our results show that perovskite-silicon tandem devices are promising candidates to significantly reduce the levelized cost of electricity and, in particular, that the ""race"" for the best silicon bottom cell is still open to all the investigated bottom cell technologies.

The integration of solar cells with supercapacitors into hybrid monolithic power packs can provide energy autonomy to smart electronic devices of the Internet of Things (IoT) by mediating between intermittent load and supply. Herein, such a photorechargeable supercapacitor (also called a photosupercapacitor) is developed via a three-electrode integration of a p-i-n halide perovskite solar cell with a gel electrolyte-type supercapacitor that uses mesoporous N-doped carbon nanospheres (MPNC) as the active electrode material. Benefiting from the large surface area, well-defined mesoporous structure, and homogeneous particle size of the MPNC material, the supercapacitor demonstrates high capacitance, resulting in large energy and power densities with a high charge/discharge efficiency. Its integration with a large-area (1 cm2) FA0.75Cs0.25Pb(I0.8Br0.2)3 perovskite solar cell, with an optimized layer sequence to minimize degradation, results in a photosupercapacitor exhibiting fast (

Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 eV in planar p-i-n tandem configuration. A methylammonium-free FA(0.75)Cs(0.25)Pb(I0.8Br0.2)(3) perovskite with high Cs content is investigated for improved stability. A 10% molarity increase to 1.1 m of the perovskite precursor solution results in approximate to 75 nm thicker absorber layers and 0.7 mA cm(-2) higher short-circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80% and up to 25.1% certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3% (absolute) over 5 months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30% tandem efficiency in the near future., Zweitver��ffentlichungen der Universit��t Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1197