@article{Haase2017b,

title = {Printable liquid silicon for local doping of solar cells},

author = {F Haase and B Lim and A Merkle and T Dullweber and R Brendel and C Günther and M H Holthausen and C Mader and O Wunnicke and R Peibst},

doi = {10.1016/j.solmat.2017.11.003},

issn = {0927-0248},

year  = {2018},

date = {2018-06-01},

journal = {Solar Energy Materials and Solar Cells},

volume = {179},

pages = {129-135},

abstract = {We demonstrate the application of a liquid-processed doped silicon precursor as a doping source for the fabrication of interdigitated back contact solar cells. We integrate phosphorus- as well as boron-doped liquid silicon in our n-type interdigitated back contact cell process based on laser-structuring. The cell with the phosphorus back surface field from liquid silicon has an efficiency of 20.9% and the cell with the boron emitter from liquid silicon has an efficiency of 21.9%. We measure saturation current densities of 34fAcm−2 on phosphorus-doped layers with a sheet resistance of 108Ω/sq and 18fAcm−2 on boron-doped layers with a sheet resistance of 140Ω/sq using passivated test samples.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Peibst2018,

title = {Building Blocks for Industrial, Screen-Printed Double-Side Contacted POLO Cells With Highly Transparent ZnO:Al Layers},

author = {R Peibst and Y Larionova and S Reiter and T F Wietler and N Orlowski and S Schäfer and B Min and M Stratmann and D Tetzlaff and J Krügener and U Höhne and J D Kähler and H Mehlich and S Frigge and R Brendel},

doi = {10.1109/JPHOTOV.2018.2813427},

issn = {2156-3381},

year  = {2018},

date = {2018-05-01},

journal = {IEEE Journal of Photovoltaics},

volume = {8},

number = {3},

pages = {719-725},

abstract = {We report on an industrial large area, screen-printed, double-side contacted cell with polysilicon on oxide (POLO) junctions on both sides and an energy conversion efficiency of 22.3% (A = 244.15 cm 2},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kruse2018,

title = {Comparison of Free Energy Loss Analysis and Synergistic Efficiency Gain Analysis for PERC Solar Cells},

author = {C N Kruse and K Bothe and R Brendel},

doi = {10.1109/JPHOTOV.2018.2802779},

issn = {2156-3381},

year  = {2018},

date = {2018-05-01},

journal = {IEEE Journal of Photovoltaics},

volume = {8},

number = {3},

pages = {683-688},

abstract = {The optimization of a solar cell requires a detailed knowledge of the efficiency limiting power losses. The free energy loss analysis (FELA) and the synergistic efficiency gain analysis (SEGA) both allow for studying these power losses. We compare both approaches for industrial passivated emitter and rear solar cells. The resistive losses calculated with both approaches are in good agreement with each other. In contrast, we find deviations of more than 20% for losses because of charge carrier recombination. From an analytical description of both methods, we conclude that these deviations are caused by a shift of the maximum power point voltage in an improved cell which is not considered in the FELA. The deviation of the losses critically depends on the specific loss channel investigated. In contrast with implied front-side power gains which are usually underestimated, rear-side or absorber gains can be over or underestimated by the FELA depending on the magnitude of the power loss. These differences follow from the Fermi level splitting which is affected differently by recombination currents at different locations. For an accurate determination of the efficiency improvement potential of individual recombination loss channels, we therefore recommend to perform a SEGA.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gemmel2018,

title = {Kerfless epitaxial silicon wafers with 7 ms carrier lifetimes and a wide lift-off process window},

author = {C Gemmel and J Hensen and L David and S Kajari-Schröder and R Brendel},

doi = {10.7567/JJAP.57.041301},

year  = {2018},

date = {2018-04-01},

journal = {Japanese Journal of Applied Physics},

volume = {57},

number = {4},

pages = {041301},

abstract = {Silicon wafers contribute significantly to the photovoltaic module cost. Kerfless silicon wafers that grow epitaxially on porous silicon (PSI) and are subsequently detached from the growth substrate are a promising lower cost drop-in replacement for standard Czochralski (Cz) wafers. However, a wide technological processing window appears to be a challenge for this process. This holds in particularly for the etching current density of the separation layer that leads to lift-off failures if it is too large or too low. Here we present kerfless PSI wafers of high electronic quality that we fabricate on weakly reorganized porous Si with etch current densities varying in a wide process window from 110 to 150 mA/cm 2 . We are able to detach all 17 out of 17 epitaxial wafers. All wafers exhibit charge carrier lifetimes in the range of 1.9 to 4.3 ms at an injection level of 10^15 cm−3 without additional high-temperature treatment. We find even higher lifetimes in the range of 4.6 to 7.0 ms after applying phosphorous gettering. These results indicate that a weak reorganization of the porous layer can be beneficial for a large lift-off process window while still allowing for high carrier lifetimes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Steinweg2018,

title = {Neues Sonnenhauskonzept mit Bauteilaktivierung statt großem Speicher},

author = {J Steinweg and S Helbig},

issn = {2195-643X},

year  = {2018},

date = {2018-03-01},

journal = {GI - Gebäudetechnik in Wissenschaft & Praxis},

volume = {2018},

number = {03},

pages = {210-221},

abstract = {Ein vom ISFH neu entwickeltes Sonnenhauskonzept (neues Sonnenhaus) hat nur noch einen kleinen Pufferspeicher, aber zusätzlich eine direkt solar beladene thermische Bauteilaktivierung. Damit wird die Gebäudemasse zum Speicher. Die Nachheizung erfolgt über eine Wärmepumpe, deren Quelle ein Erdwärmekollektor ist. Durch solare Regeneration mit sommerlichen Kollektorüberschüssen kann dieser viermal kleiner dimensioniert werden als üblich. Zudem wird hierdurch die sommerliche Stagnation der solarthermischen Kollektoren vermieden. Der Beitrag zeigt die über zwei Jahre gemessene Systemperformance eines Experimentalgebäudes in Hannover. Der spezifische Gesamtstromverbrauch liegt bei etwa qEE = 8 kWh/m²a für die vollständige Wärmeversorgung. Ein System- und Kostenvergleich zeigt, dass der Systemprototyp bereits 28 % günstiger ist als Standard-Sonnenhauskonzepte. Weitere Systemvereinfachungen erreichen – bei gleicher Endenergieeinsparung – eine Kostenersparnis von bis zu 35 %.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pazidis2018b,

title = {Magnetron sputtered TiOx layers: Structural, electrical, optical and thermochromic aspects},

author = {A Pazidis and R Reineke-Koch},

doi = {10.1016/j.tsf.2017.12.019},

issn = {0040-6090},

year  = {2018},

date = {2018-03-01},

journal = {Thin Solid Films},

volume = {649},

pages = {43-50},

abstract = {Titanium oxide layers were prepared by sputter deposition with plasma emission monitoring in the whole stoichiometry range between Ti and TiO2 without and with substrate heating to 240 °C. The layers were characterized with regard to their crystal structure and specific resistance. Optical constants were determined in the spectral range between 240 nm and 38 μm. The thermochromic behavior of a prepared Ti2O3 layer was measured and compared to calculations for bulk material.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bothe2018,

title = {Accuracy of Simplifications for Spectral Responsivity Measurements of Solar Cells},

author = {K Bothe and D Hinken and B Min and C Schinke},

doi = {10.1109/JPHOTOV.2018.2793758},

issn = {2156-3381},

year  = {2018},

date = {2018-03-01},

journal = {IEEE Journal of Photovoltaics},

volume = {8},

number = {2},

pages = {611-620},

abstract = {The determination of the spectral responsivity is an essential part of solar cell characterization. Since solar simulators only approximate the reference spectrum, a spectral mismatch correction has to be performed. This correction procedure requires spectral responsivity data. Apart from the complete differential spectral responsivity procedure, the IEC 60904-8 standard defines four simplifications. In this paper, we provide information on the variations in the spectral responsivity curves for these simplifications. We show that for nonlinear front junction cells, deviations predominantly occur at wavelengths above 700 nm and become largest around 1000 nm. While we found a maximum deviation of 30% for the simplification with lowest requirements in bias irradiance, all other simplifications yield deviations below 10%. For a nonlinear cell measured relative to a world photovoltaic scale reference cell using a class A solar simulator, this transfers to a deviation below 0.01% in the spectral mismatch factor. If one depends on the use of a simplification, we recommend using the multicolor approach. Even though the singlecolor approach might yield lower deviations, this approach requires knowledge about the maximum in the spectral responsivity, which is not generally known in advance of the measurement. Accepting a slightly higher deviation, the white bias approach is a recommendable alternative.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zielke2018,

title = {Large-Area PEDOT:PSS/c-Si Heterojunction Solar Cells With Screen-Printed Metal Contacts},

author = {D Zielke and R Gogolin and M -U Halbich and C Marquardt and W Lövenich and R Sauer and J Schmidt},

doi = {10.1002/solr.201700191},

issn = {2367-198X},

year  = {2018},

date = {2018-03-01},

journal = {Solar RRL},

volume = {2},

number = {3},

pages = {1700191},

abstract = {A large‐area BackPEDOT solar cell with a phosphorus‐diffused emitter and a high‐temperature‐fired screen‐printed Ag grid on the front surface and PEDOT:PSS as hole‐collecting and passivating layer at the cell rear is developed. As base material, 15.6 × 15.6 cm2 pseudo‐square industrial‐type boron‐doped p‐type Czochralski‐grown silicon wafers are used. The set‐peak firing temperature (Tset) is varied from 850 to 870 °C with a total number of 32 processed solar cells. The optimum Tset of 870 °C results in a median solar cell efficiency of 19.0%. The best large‐area BackPEDOT solar cell achieves an efficiency of 20.2%. Based on external quantum efficiency measurements, a rear surface recombination velocity Srear < 70 cm s−1 is determined, a value which is on a par with today's industrial high‐efficiency solar cells. Furthermore, a low‐temperature metal paste is introduced, which is shown to be capable of metalizing the PEDOT:PSS‐covered rear surface of the solar cells without damaging the rear surface passivation. The principle feasibility of such a rear metallization scheme is demonstrated. The parasitic absorption of infrared light within the PEDOT:PSS layer is identified as the major loss mechanism in the current cells, which might be overcome in the future by adding infrared‐transparent additives to the PEDOT:PSS dispersion.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Haase2018,

title = {Perimeter Recombination in 25%-Efficient IBC Solar Cells With Passivating POLO Contacts for Both Polarities},

author = {F Haase and S Schäfer and C Klamt and F Kiefer and J Krügener and R Brendel and R Peibst},

doi = {10.1109/JPHOTOV.2017.2762592},

issn = {2156-3381},

year  = {2018},

date = {2018-01-01},

journal = {IEEE Journal of Photovoltaics},

volume = {8},

number = {1},

pages = {23-29},

abstract = {We introduce a method for the quantification of perimeter recombination in solar cells based on infrared lifetime measurements. We apply this method at a 25.0%-efficient interdigitated back contact (IBC) silicon solar cell with passivating contacts. The implied pseudo-efficiency determined by infrared lifetime mapping is 26.2% at an intermediate process step. The 1.2%abs loss is attributed to a process-related reduction in surface passivation quality, recombination in the perimeter area, and series resistance. The 2 × 2 cm2 -sized cell is processed on a 100 mm wafer. We determine the implied pseudo-efficiency with illuminated and with shaded perimeter area during infrared lifetime mapping. The difference between both implied pseudo-efficiencies yields the efficiency loss by perimeter recombination, which is determined to be 0.4%abs for a wafer resistivity of 1.3 Ω cm and even 0.9%abs for a wafer resistivity of 80 Ω cm.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bredemeier2018,

title = {Possible Candidates for Impurities in mc-Si Wafers Responsible for Light-Induced Lifetime Degradation and Regeneration},

author = {D Bredemeier and D C Walter and J Schmidt},

doi = {10.1002/solr.201700159},

issn = {2367-198X},

year  = {2018},

date = {2018-01-01},

journal = {Solar RRL},

volume = {2},

number = {1},

pages = {1700159},

abstract = {We examine the light‐induced carrier lifetime degradation and regeneration at elevated temperature in multicrystalline silicon (mc‐Si) wafers of different thicknesses. The experimental results show that the thinner the wafer the less pronounced the degradation is and the faster the regeneration takes place. We interpret this result in the framework of a recently proposed defect model, where the lifetime regeneration is attributed to the diffusion of the recombination‐active impurity to the wafer surfaces, where it is permanently trapped. Modeling the measured thickness‐dependent lifetime evolutions enables us to determine the diffusion coefficient of the impurity to be in the range (5 ± 2) × 10−11 cm2 s−1 at a temperature of 75 °C. Comparing the diffusion coefficient extracted from our measurements with data published in the literature allows us to exclude most impurities. Despite the large uncertainties in the diffusion coefficient data reported in the literature, reasonable agreement is only obtained for nickel, cobalt, and hydrogen. One important practical implication of our study is that mc‐Si wafers thinner than 120 μm do not suffer from pronounced light‐induced lifetime degradation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Veith-Wolf2018,

title = {Spectra-Dependent Stability of the Passivation Quality of Al2O3/c-Si Interfaces},

author = {B Veith-Wolf and R Witteck and A Morlier and H Schulte-Huxel and M R Vogt and J Schmidt},

doi = {10.1109/JPHOTOV.2017.2775147},

issn = {2156-3381},

year  = {2018},

date = {2018-01-01},

journal = {IEEE Journal of Photovoltaics},

volume = {8},

number = {1},

pages = {96-102},

abstract = {We examine the stability of the c-Si surface passivation quality by spatial atomic-layer-deposited aluminum oxide (Al2O3), plasma-enhanced chemical vapor deposited silicon nitride (SiNx), and Al2O3/SiNx stacks under illumination with two different spectra. The Al2O3-passivated c-Si surfaces annealed at 350 °C show a weak degradation due to UV illumination, with surface recombination velocities (SRVs) of 122 cm/s after receiving a ultraviolet (UV) dose of 275 kWh/m2. Silicon samples passivated with Al2O3 layers that received a fast-firing step show an improvement due to UV illumination with a reduction of the SRVs initially from 14 to 5 cm/s for single Al2O3 layers. For the fired Al2O3 layers the negative fixed charge density increases from -6×1012 cm-2 up to -1.2×1013 cm-2 during UV illumination. We demonstrate that for the SiNx and the fired Al2O3 single layers, photons with energy greater than 3.4 eV are necessary to reduce the passivation quality. In contrast, low-temperature-annealed Al2O3 single layers and nonfired Al2O3/SiNx stacks showed a degradation already under illumination with a halogen lamp. Importantly, we observe a perfectly stable passivation on boron-diffused p+ emitter for fired Al2O3/SiNx stacks featuring a stable saturation current density of 18 fA/cm2 for a p+ sheet resistance of 90 Ω/sq.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Walter2017b,

title = {On the equilibrium concentration of boron-oxygen defects in crystalline silicon},

author = {D C Walter and R Falster and V V Voronkov and J Schmidt},

doi = {10.1016/j.solmat.2017.06.036},

isbn = {0927-0248},

year  = {2017},

date = {2017-12-01},

journal = {Solar Energy Materials and Solar Cells},

volume = {173},

pages = {33-36},

abstract = {We determine the equilibrium concentration of the BO defect in boron-doped Czochralski-grown silicon after prolonged (up to 150 h) annealing at relatively low temperatures between 200 and 300 °C. We show that after sample processing, the BO concentration has not necessarily reached the equilibrium state. The actually reached state depends on the detailed temperature profile of the last temperature treatment before the light-induced degradation (LID) is performed. For the investigated Cz-Si materials with base resistivities ranging between 0.5 and 2.5 Ω cm, we observe that an annealing step at 200 °C for 50 h establishes the equilibrium, independent of the base resistivity. Experiments performed at different temperatures reveal that the equilibrium defect concentration decreases with increasing annealing temperature. This observation can be understood, assuming a mobile species which is distributed between at least two different sinks. A possible defect model is discussed.},

note = {Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Krügener2017b,

title = {Improvement of the SRH bulk lifetime upon formation of n-type POLO junctions for 25% efficient Si solar cells},

author = {J Krügener and F Haase and M Rienäcker and R Brendel and H J Osten and R Peibst},

doi = {10.1016/j.solmat.2017.05.055},

issn = {0927-0248},

year  = {2017},

date = {2017-12-01},

journal = {Solar Energy Materials and Solar Cells},

volume = {173},

pages = {85-91},

abstract = {Carrier-selective contact schemes, like polysilicon on oxide (POLO), provide low contact resistivities while preserving an excellent passivation quality. These junctions offer an important additional feature compared to a-Si/c-Si heterojunctions. We find that the formation of n-type POLO junctions lead to a huge increase of the Shockley-Read-Hall (SRH) lifetime of the substrate, a prerequisite for highly efficient solar cells. The SRH lifetime improvement can be observed for both bulk polarities and for a variety of bulk resistivities. Thus we suggest that the highly doped POLO junction getters impurities that have more or less symmetric SRH capture cross sections. We are able to achieve SRH lifetimes of > 50 ms. By applying POLO junctions to interdigitated back contact cells, we achieve cells with an efficiency of 25%.},

note = {Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tetzlaff2017c,

title = {A simple method for pinhole detection in carrier selective POLO-junctions for high efficiency silicon solar cells},

author = {D Tetzlaff and J Krügener and Y Larionova and S Reiter and M Turcu and F Haase and R Brendel and R Peibst and U Höhne and J -D Kähler and T F Wietler},

doi = {10.1016/j.solmat.2017.05.041},

issn = {0927-0248},

year  = {2017},

date = {2017-12-01},

journal = {Solar Energy Materials and Solar Cells},

volume = {173},

pages = {106-110},

abstract = {Polycrystalline silicon (poly-Si) layers on thin silicon oxide films have received strong research interest as they form excellent carrier selective junctions on crystalline silicon substrates after appropriate thermal processing. Recently, we presented a new method to determine the pinhole density in interfacial oxide films of poly-Si on oxide (POLO)-junctions with excellent electrical properties. The concept of magnification of nanometer-size pinholes in the interfacial oxide by selective etching of the underlying crystalline silicon is used to investigate the influence of annealing temperature on pinhole densities. Eventually, the pinholes are detected by optical microscopy and scanning electron microscopy. We present results on the pinhole density in POLO-junctions with J0 values as low as 1.4 fA/cm2. The stability of this method is demonstrated by proving that no new holes are introduced to the oxide during the etching procedure for a wide range of etching times. Finally, we show the applicability to multiple oxide types and thickness values, differently doped poly-Si layers as well as several types of wafer surface morphologies. For wet chemically grown oxides, we verified the existence of pinholes with an areal density of 2×10^7 cm−2 even already after annealing at a temperature of 750 °C (lower than the optimum annealing temperature for these junctions).},

note = {Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics},

keywords = {},

pubstate = {published},

tppubtype = {article}

}