@article{Schulte-Huxel2024,

title = {Novel busbar design for screen-printed front side Al metallization of high-efficiency solar cell},

author = {H Schulte-Huxel and T Daschinger and B Min and T Brendemühl and R Brendel},

doi = {10.1016/j.solmat.2023.112601},

issn = {0927-0248},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Solar Energy Materials and Solar Cells},

volume = {264},

pages = {112601},

abstract = {The need to reduce the silver consumption for future global PV production requires novel approaches for cell metallization and module integration. A screen-printed aluminum cell metallization on the front side could contribute here, but requires a redesign of the solder pads and busbars. A compromise between shading and resistive losses is needed. We investigate the inclusion of Ag solder pads in high-aspect-ratio Al finger grids on the front side of p-type back junction solar cells featuring passivating polysilicon on oxide (POLO) contacts on the rear side. In order to determine the optimal geometric dimensions of the solder pads, we characterize the resistance at the interface between the Ag solder pads and the Al finger grid in dependence on the size of the overlap between the two paste. A contact resistance of 285 mΩ is determined for 200 μm-narrow Al busbars and small solder pads of 750 μm in length. This would require tens of solder pads per busbar for acceptable power losses below 0.5 % coming along with significant shading. Therefore, a new metallization design is developed. We use narrow Ag busbars with a widened intersection to the Al fingers in order to reduce the contact resistance caused by the Ag–Al alloy. Thereby, the shading losses of the solderable busbars and pads are less than 1.5 %.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Herz2023,

title = {Identify, analyse and mitigate—Quantification of technical risks in PV power systems},

author = {M Herz and G Friesen and U Jahn and M Koentges and S Lindig and D Moser},

doi = {10.1002/pip.3633},

year  = {2023},

date = {2023-12-01},

urldate = {2023-01-01},

journal = {Progress in Photovoltaics: Research and Applications},

volume = {31},

number = {12},

pages = {1285-1298},

abstract = {Technical risks are important criteria to consider when investing in new and existing PV installations. Quantitative knowledge of these risks is one of the key factors for the different stakeholders, such as asset managers, banks or project developers, to make reliable business decisions before and during the operation of their PV assets. Within the IEA PVPS Task 13 Expert Group, we aim to increase the knowledge on methodologies to assess technical risks and mitigation measures in terms of economic impact and effectiveness. The developed outline provides a reproducible and transparent technique to manage the complexity of risk analysis and processing in order to establish a common practice for professional risk assessment. Semi-quantitative and quantitative methodologies are introduced to assess technical risks in PV power systems and provide examples of common technical risks described and rated in the new created PV failure fact sheets (PVFS). Besides the PVFS based on expert knowledge and expert opinion, an update on the statistics of the PV failure degradation survey is given. With the knowledge acquired and data collected, the risk and cost–benefit analysis is demonstrated in a case study that shows methods for prioritising decisions from an economic perspective and provided important results for risk managing strategies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tous2023,

title = {Overview of key results achieved in H2020 HighLite project helping to raise the EU PV industries' competitiveness},

author = {Loic Tous and Jonathan Govaert and Samuel Harrison and Carolyn Carrière and Vincent Barth and Valentin Giglia and Florian Buchholz and Ning Chen and Andreas Halm and Antonin Faes and Gizem Nogay and Hugo Quest and Torsten Roessler and Tobias Fellmeth and Dirk Reinwand and Hannah Stolzenburg and Florian Schindler and Max Mittag and Arnaud Morlier and Matevz Bokalic and Kristijan Brecl and Miha Kikelj and Marko Topic and Josco Kester and Stefan Wendlandt and Marco Galiazzo and Alessandro Voltan and Giuseppe Galbiati and Marc Estruga Ortiga and Frank Torregrosa and Michael Grimm and Julius Denafas and Tadas Radavicius and Povilas Lukinskas and Tuukka Savisalo and Thomas Regrettier and Ivan Gordon},

doi = {10.1002/pip.3667},

year  = {2023},

date = {2023-12-01},

urldate = {2023-01-12},

journal = {Progress in Photovoltaics: Research and Applications},

volume = {31},

issue = {12},

pages = {1409-1427},

abstract = {The EU crystalline silicon (c-Si) PV manufacturing industry has faced strong foreign competition in the last decade. To strive in this competitive environment and differentiate itself from the competition, the EU c-Si PV manufacturing industry needs to (1) focus on highly performing c-Si PV technologies, (2) include sustainability by design, and (3) develop differentiated PV module designs for a broad range of PV applications to tap into rapidly growing existing and new markets. This is precisely the aim of the 3.5 years long H2020 funded HighLite project, which started in October 2019 under the work program LC-SC3-RES-15-2019: Increase the competitiveness of the EU PV manufacturing industry. To achieve this goal, the HighLite project focuses on bringing two advanced PV module designs and the related manufacturing solutions to higher technology readiness levels (TRL). The first module design aims to combine the benefits of n-type silicon heterojunction (SHJ) cells (high efficiency and bifaciality potential, improved sustainability, rapidly growing supply chain in the EU) with the ones of shingle assembly (higher packing density, improved modularity, and excellent aesthetics). The second module design is based on the assembly of low-cost industrial interdigitated back-contact (IBC) cells cut in half or smaller, which is interesting to improve module efficiencies and increase modularity (key for application in buildings, vehicles, etc.). This contribution provides an overview of the key results achieved so far by the HighLite project partners and discusses their relevance to help raise the EU PV industries' competitiveness. We report on promising high-efficiency industrial cell results (24.1% SHJ cell with a shingle layout and 23.9% IBC cell with passivated contacts), novel approaches for high-throughput laser cutting and edge re-passivation, module designs for BAPV, BIPV, and VIPV applications passing extended testing, and first 1-year outdoor monitoring results compared with benchmark products.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Schulte-Huxel2022c,

title = {Optimal interconnection of three-terminal tandem solar cells},

author = {H Schulte-Huxel and R Witteck and S Blankemeyer and M Köntges},

doi = {10.1002/pip.3643},

year  = {2023},

date = {2023-12-01},

urldate = {2022-11-13},

journal = {Progress in Photovoltaics: Research and Applications},

volume = {31},

issue = {12},

pages = {1350-1359},

abstract = {Three-terminal (3T) tandem solar cells require an adapted module integration scheme in order to explore their full efficiency potential. The three terminals allow to extract the power of the top and bottom cell separately. In a cell string, the wide bandgap top cells are interconnected in parallel to multiple bottom cells resulting in a parallel/series interconnection. This interconnection scheme affects the operation of the subcells, the resulting current path between the subcells, the layout of the cell interconnects, and the system level. Here, we analyze by simulations and experiments the aspects of the module integration of series- and reverse-connected 3T cells with their practical impact on module processes and performance as well as the effect of varying voltage ratios on the string-end losses. If the subcells are connected in series, the module integration requires insulation layers and significantly longer interconnects compared to devices with reverse-connected subcells. Tandem devices with a reverse connection and a voltage ratio between top and bottom cell of 2:1 allow a lean interconnection design and low integration losses. We present an approach for the integration of bypass diodes for the protection against shading effects that allow to minimize string-end and shading losses for a system of modules featuring 3T cells.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bothe2023b,

title = {Extended FF and VOC Parameterizations for Silicon Solar Cells},

author = {K Bothe and D Hinken and R Brendel},

doi = {10.1109/JPHOTOV.2023.3309932},

year  = {2023},

date = {2023-11-01},

urldate = {2023-09-14},

journal = {IEEE Journal of Photovoltaics},

volume = {13},

issue = {6},

pages = {787-792},

abstract = {This work is concerned with maximal and currently obtained fill factors of crystalline silicon solar cells. Recent research activities have led to a drastically decreased recombination in the volume as well as at the surfaces and interfaces of crystalline silicon solar cells. As a result, open-circuit voltages (VOC) and fill factor (FF) values increased significantly. In order to classify how good the achieved improvements are, it is necessary to know the maximum achievable values. Unfortunately, there is no explicit expression for the FF in terms of other characteristic solar cell parameters. For this reason, the empirical FF0 -relation by Green is widely used to predict upper FF bounds for a given VOC . In order to evaluate to what extent Green's relation is a good approximation to recently obtained values, we study FF – VOC relations for ideal resistance-free single junction silicon solar cells limited by intrinsic recombination using state-of-the-art analytical models. The obtained upper bounds are compared with recently published record values showing that all values stay below the intrinsic limit. We provide parameterizations of VOC and FF as a function of sample thickness w and base dopant density Ndop .},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Winter2023b,

title = {Impact of Fast-Firing Conditions on Light- and Elevated-Temperature-Induced Degradation (LeTID) in Ga-Doped Cz–Si},

author = {M Winter and D C Walter and J Schmidt},

doi = {10.1109/JPHOTOV.2023.3304118},

year  = {2023},

date = {2023-11-01},

urldate = {2023-08-30},

journal = {IEEE Journal of Photovoltaics},

volume = {13},

issue = {6},

pages = {849-857},

abstract = {The fast-firing step commonly applied at the end of solar cell production lines triggers ``Light- and elevated-Temperature-Induced Degradation” (LeTID) effects of the carrier lifetime in Ga-doped Cz–Si wafers and solar cells made thereof. As far as the defect formation within the silicon bulk is concerned, the key parameters of the fast-firing step are the peak firing temperature ( FT ) and the band velocity v band of the conveyor belt, where the latter mainly defines the cooling ramp after the firing peak. In this contribution, we show that the extent of LeTID and the dependence on the applied temperature during degradation increase strongly with increasing measured FT (from 680 °C to 800 °C), v band (from 2.8 to 7.2 m/min), and the refractive index n of the hydrogen-rich silicon nitride layer deposited on the wafer surfaces (from 2.07 to 2.37). Through temperature-dependent degradation experiments, we determine an activation energy of E A = (0.55 ± 0.10) eV of the LeTID mechanism in Ga-doped Cz–Si, which is independent of FT and v band . From this observation we conclude that a single defect activation mechanism is most likely responsible for the examined LeTID effect, independent of the firing conditions. However, the concentration of recombination-active defect centers after LeTID depends critically on FT , v band , and n , which we attribute to variations of the in-diffused hydrogen concentrations from the silicon nitride layers during firing. Our experiments hence point towards an involvement of hydrogen in the LeTID mechanism observed in Ga-doped Cz–Si.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Liu2023,

title = {Influence of site characteristics on the performance of shallow borehole heat exchanger arrays: A sensitivity analysis},

author = {Q Liu and F Weiland and P Pärisch and N Kracht and M Huang and T Ptak},

doi = {10.1016/j.geothermics.2023.102785},

issn = {0375-6505},

year  = {2023},

date = {2023-11-01},

urldate = {2023-01-01},

journal = {Geothermics},

volume = {114},

pages = {102785},

abstract = {Using borehole heat exchangers (BHE) to extract shallow geothermal energy has grown rapidly in recent years. How to maintain a long-term balanced, sustainable operation of the BHE arrays becomes a key issue. Site characteristics, including hydrogeological and geothermal conditions as well as spatial distribution of subsurface physical parameters, are generally idealized or partly neglected in practice. To investigate the consequences of such simplifications, a 3D model, based on data from a planned real site, is established to consider groundwater flow, subsurface heterogeneity, and various hydrogeothermal boundary conditions. After verifying the model, a sensitivity analysis is conducted. Nine factors regarding site characteristics are selected, including Darcy flux in the aquifer, thermal conductivity and volumetric heat capacity of the ground, groundwater depth, thermal and hydraulic heterogeneity, geothermal gradient, heat transfer coefficient on the ground surface and seasonal rainfall. Sensitivity results indicate that the annual total heat production is most sensitive to geothermal gradient, followed by Darcy flux, both of which have positive effects. Groundwater depth and heat transfer coefficient have negative effects on annual heat production. Compared to thermal heterogeneity and rainfall, the influence of hydraulic heterogeneity is higher. Uncertainty of annual heat production due to various Peclet numbers is quantified through regression analysis.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}