As the efficiency of perovskite silicon tandem solar cells is increasing, the upscaling for industrial production is coming into focus. Spatially resolved, quantitative, fast, and reliable contactless measurement techniques are demanded for quality assurance and to pinpoint the cause of performance losses in perovskite silicon tandem solar cells. In this publication we present a measurement method based on spectrally integrated photoluminescence (PL) imaging to extract subcell-selective implied open-circuit ( i V oc ) images from monolithic perovskite silicon tandem solar cells. We validate the approach using spectrally resolved absolute PL measurements based on an integrating sphere for the perovskite top cell and PL-calibrated carrier lifetime images for the silicon bottom cell. Additionally, V oc measurements of solar cells with low contact losses are used to validate the new measurement technique. We find a good agreement of the i V oc images with the validating measurements with a maximum deviation of well below 1 % compared to the validation measurements.
Up-scaling of perovskite solar cells and modules requires both the development of suitable laser patterning processes for series interconnection of the cells and the quantification of the spatial distribution of solar cell parameters. Here, we investigate perovskite solar cells patterned with ns and ps laser pulses at varying laser fluences and analyze them with hyperspectral photoluminescence (PL) imaging. Based on these images, mappings of the distribution of the central PL wavelength, the quasi-Fermi-level splitting, the Urbach energy and the shunt resistance were calculated. From the behavior of these parameters, particularly in the vicinity of the laser trenches, we infer laser-material interaction processes and their influence on the electrical performance of the interconnected cells. It is shown that both ps and ns laser pulses can be used for successful series interconnection with low electrical losses in a very narrow edge regions, provided that the fluence is carefully adjusted.
Each solar cell is characterized at the end-of-line using current-voltage ( IV) measurements, except shingle cells, due to multiplied measurement efforts. Therefore, the respective host cell quality is adopted for all resulting shingles, which is sufficient for samples with laterally homogeneous quality. Yet, for heterogeneous defect distributions, this procedure leads to (i) loss of high quality shingles due to defects on neighboring host cell parts, (ii) increased mismatch losses due to inaccurate binning and (iii) lack of shingle-precise characterization. In spatially resolved host measurements, such as electroluminescence images, all shingles are visible along with their properties. Within a comprehensive experiment 840 hosts and their resulting shingles are measured. Thereafter, a deep learning model has been designed and optimized which processes host-images and determines IV parameters like efficiency or fill factor, IV curves and binning classes for each shingle cell. The efficiency can be determined with an error of 0 .06 % abs enabling a 13 % abs improvement in correct assignment of shingles to bin classes compared to industry standard. This results in lower mismatch losses and higher output power on module level as demonstrated within simulations. Also IV curves of defective and defect-free shingle cells can be derived with good agreement to actual shingle measurements.
This study focuses on electron-selective passivating contacts for crystalline silicon (c-Si) solar cells where an interlayer is used to provide a low contact resistivity between the c-Si substrate and the metal electrode. These electron contact interlayers are used in combination with other passivating interlayers (e.g., a-Si:H, TiO2, and Nb2O5) to improve surface passivation whilst still permitting contact resistivities suitable for high efficiency solar cells. We show that a wide variety of thermally evaporated materials, most of which have ionic character, enable an Ohmic contact between n-type c-Si and Al. From this pool of compounds, we observed that CsBr has especially promising behavior because of its excellent performance and thermal stability when combined with thin passivating layers. With different test structures, we were able to demonstrate low contact resistance using TiO2/CsBr, Nb2O5/CsBr and a-Si:H/CsBr stacks on n-type c-Si. The quality of the provided surface passivation depended on the stack but we achieved the best overall passivation stability with TiO2/CsBr. Finally, we were able to demonstrate an efficiency >20% on a laboratory-scale solar cell that implements the TiO2/CsBr/Al stack as full-area rear side electron selective contact.
Increased deployment of solar PV enables the transition to decarbonized energy systems, capable of tempering the dire consequences of global warming. Even though backsheets are very important regarding lifetime energy yield of the PV module, the environmental impacts of their production, use and end-of-life (EoL) processing are largely neglected. As part of a recently finalized Dutch national project EXTENSIBLE (Energy yield assessment of neXT gENeration and SustaInaBLE backsheets) the environmental impacts for 7 different polymeric backsheets have been evaluated via a life cycle assessment (LCA). The selected backsheets include 3 traditional polyethylene terephthalate (PET) - based backsheets with a fluorine containing outer layer (two white pigmented and one fully transparent). The other 4 backsheets are novel high-performance polyolefin (PO) -based backsheets, manufactured by Endurans Solar ™, also including one transparent version. From results of the LCA it is concluded that in comparison with PET-based backsheets and fluoropolymer containing backsheets, PO-based backsheets perform best in terms of energy yield, reliability and environmental impacts. The production of fluoropolymer- and PET-based backsheets cause substantial environmental impacts, especially regarding climate change and ozone depletion. This conclusion is corroborated by recent literature data. Regarding the EoL phase, it was shown from a theoretical assessment that pyrolysis of the spent backsheets potentially leads to much lower GWP when compared to incineration, especially for the PO-based backsheets. Incineration of the shredded and solid backsheet material causes direct emissions of CO 2 with a limited heat recovery potential only. Deploying pyrolysis for spent PO-based backsheets significantly improves their life-time GWP per kWh produced. Pyrolysis offers the possibility to recover a large part of the polyolefin as an usable pyrolysis oil that might serve as feedstock for chemicals or as transportable liquid fuel for the generation of process heat in recovery boilers, thereby avoiding the use of new fossil resources. EoL pyrolysis (or incineration) of fluoropolymer-based backsheets is problematic due to the presence of fluorinated hydrocarbons, leading to corrosive and/or toxic products.
Efficient metal contact formation is pivotal for the production of cost-effective, high-performance crystalline silicon (Si) solar cells. Traditionally, screen-printed silver (Ag) contacts on the front surface have dominated the industry, owing to their simplicity, high throughput, and significant electrical benefits. However, the high cost associated with using over 13-20mg/Wp of Ag can impede the development of truly cost-effective solar cells. Therefore, there is an urgent need to explore alternative, economically viable metals compatible with silicon substrates. This study reports on the application of a contact stack consisting of Ag, nickel (Ni), and copper (Cu) in Si solar cells. To prevent Schottky contact formation, Ag is implemented as a seed layer, while Ni and Cu form the metal bulk layer. The fabricated bi-layer stack without selective emitter exhibits a maximum efficiency of ~21.5%, a fill factor of 81.5%, and an average contact resistance of 5.88mΩ·cm 2 for a monofacial PERC cell. Microstructure analysis demonstrate that the metals within the contacts remain distinct, and Cu diffusion into the silicon during the firing process is absent. Consequently, printed bi-layer contacts emerge as a promising alternative to Ag contacts, reducing the Ag consumption to below 2.5mg/Wp per cell without compromising overall efficiency.
Compound/silicon heterojunction (SCH) solar cells have been widely studied due to the low parasitic absorption of the window layer, high short-circuit current, and simple preparation process. So far, most reported SCH solar cells are small-area devices. By depositing MoO x hole transport layer using hot-wire oxidation-sublimation deposition technique and employing a front-contact back-junction cell architecture, the large-area SCH solar cells are successfully fabricated on M6 (166 mm) n-type silicon wafers. Indium cerium oxide (ICO) film with the optimal thickness of about 110 nm is inserted between MoO x and Ag. The ICO/Ag stack functions well as a back reflector and is beneficial for increasing the short-circuit current density, reducing the contact resistance, and improving the device stability. A power conversion efficiency of 21.59% is achieved on the champion SCH solar cell with the device area of 274.15 cm 2.
Organic photovoltaics (OPV) has attracted tremendous attention as a promising alternative to silicon wafer-based technologies for building integration. While significant progress has been achieved on the power conversion efficiency of OPV technologies, their field stability is rarely studied. This work investigates the field performance and reliability of a large-area OPV module designed for BIPV application in the tropical region of Singapore for 4.5 years. The device suffered more than 14% degradation in power at the standard testing conditions from the initial performance, largely due to losses in fill factor (-12% relative). During the monitoring period, it exhibited comparable performance to more conventional silicon PV technologies, with an average specific energy yield of about 4 kWh/kWp/day and an average performance ratio of 0.96. Excellent performance at low light conditions was also observed. However, its field performance was heavily impacted by soiling, which typically led to a 5 to 10% loss in the current output after several months. Further, the device’s outdoor performance also showed a three-stage degradation process, including (1) an initial slow degradation in the first two years (about -1%/year), (2) a stable period with negligible performance loss from year 2 to year 3.5 and (3) a rapid degradation in the last year (about -5%/year).
With the improvement of surface passivation, bulk recombination is becoming an indispensable and decisive factor to assess the limiting efficiency ( η lim ) of crystalline silicon (c-Si) solar cells. In simultaneous consideration of surface and bulk recombination, a modified model of η lim evaluation is developed. Surface recombination is directly depicted with contact selectivity while bulk recombination is revised on the aspects of ideality factor and wafer thickness. The η lim of cutting-edge photovoltaic technologies, double-side tunneling-oxide passivating contact (TOPCon) and silicon heterojunction (SHJ) solar cells, are numerically simulated using the new model as 28.73% and 29.00%, respectively. Hybrid solar cells consisting of n-type TOPCon contact and p-type SHJ contact can approach an η lim as high as 29.18% at the optimal wafer thickness ( W opt ) of 103 μm . Our results are instructive in accurately assessing efficiency potential and accordingly optimizing design strategies of c-Si solar cells.