@article{Helmich2021c,

title = {Impact of hydrogen on the boron-oxygen-related lifetime degradation and regeneration kinetics in crystalline silicon},

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

doi = {10.1016/j.solmat.2021.111340},

issn = {0927-0248},

year  = {2021},

date = {2021-10-01},

journal = {Solar Energy Materials and Solar Cells},

volume = {232},

pages = {111340},

abstract = {We examine the impact of hydrogen on the boron-oxygen-related lifetime degradation and regeneration kinetics in boron-doped p-type Czochralski-grown silicon wafers. We introduce the hydrogen into the silicon bulk by rapid thermal annealing. The hydrogen source are hydrogen-rich silicon nitride (SiNx:H) layers. Aluminum oxide (Al2O3) layers of varying thickness are placed in-between the silicon wafer surfaces and the SiNx:H layers. By varying the Al2O3 thickness, which acts as an effective hydrogen diffusion barrier, the hydrogen bulk content is varied over more than one order of magnitude. The hydrogen content is determined from measured wafer resistivity changes. In order to examine the impact of hydrogen on the degradation kinetics, all samples are illuminated at a light intensity of 0.1 suns near room temperature. We observe no impact of the in-diffused hydrogen content on the degradation rate constant, confirming that hydrogen is not involved in the boron-oxygen degradation mechanism. The regeneration experiments at 160°C and 1 sun, however, show a clear dependence on the hydrogen content with a linear increase of the regeneration rate constant with increasing bulk hydrogen concentration. However, extrapolation of our measurements toward a zero in-diffused hydrogen content shows that the regeneration is still working even without any in-diffused hydrogen. Hence, our measurements demonstrate that there are two distinct regeneration processes taking place. This is in good agreement with a recently proposed defect reaction model and is also in agreement with the finding that the permanent boron-oxygen deactivation also works on non-fired solar cells, though at a lower rate.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hollemann2021c,

title = {Changes in hydrogen concentration and defect state density at the poly-Si/SiOx/c-Si interface due to firing},

author = {C Hollemann and N Folchert and S P Harvey and P Stradins and D L Young and C Lima Salles Souza and M Rienäcker and F Haase and R Brendel and R Peibst},

doi = {10.1016/j.solmat.2021.111297},

issn = {0927-0248},

year  = {2021},

date = {2021-10-01},

journal = {Solar Energy Materials and Solar Cells},

volume = {231},

pages = {111297},

abstract = {We determined the density of defect states of poly-Si/SiOx/c-Si junctions featuring a wet chemical interfacial oxide from lifetime measurements using the MarcoPOLO model to calculate recombination and contact resistance in poly-Si/SiOx/c-Si-junctions. In samples that did not receive any hydrogen treatment, the Dit,cSi is about 2 × 1012 cm−2 eV⁻1 before firing and rises to 3–7 × 1012 cm⁻2 eV⁻1 during firing at measured peak temperatures between 620 °C and 863 °C. To address the question of why AlOx/SiNy stacks in contrast to pure SiNy layers for hydrogenation during firing provides better passivation quality, we have measured the hydrogen concentrations at the poly-Si/SiOx/c-Si interface as a function of AlOx layer thickness and compared these to J0 and calculated Dit,c-Si values. We observe an increase of the hydrogen concentration at the SiOx/c-Si interface upon firing as a function of the firing temperature that exceeds the defect concentrations at the interface several times. However, the AlOx layer thickness appears to cause an increase in hydrogen concentration at the SiOx/c-Si interface in these samples rather than exhibiting a hydrogen blocking property.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gewohn2021b,

title = {Predicting color and short-circuit current of colored BIPV modules},

author = {T Gewohn and C Schinke and B Lim and R Brendel},

doi = {10.1063/5.0063140},

year  = {2021},

date = {2021-09-01},

journal = {AIP Advances},

volume = {11},

number = {9},

pages = {095104},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wehmeier2021b,

title = {Inkjet-Printed In Situ Structured and Doped Polysilicon on Oxide Junctions},

author = {N Wehmeier and F Kiefer and T Brendemühl and L Mettner and S J Wolter and F Haase and R Peibst and M Holthausen and D Mispelkamp and C Mader and C Daeschlein and O Wunnicke and S Kajari-Schröder},

doi = {10.1109/JPHOTOV.2021.3094131},

year  = {2021},

date = {2021-09-01},

journal = {IEEE Journal of Photovoltaics},

pages = {1-9},

abstract = {We investigate the inkjet printing of liquid silicon ink to form in situ doped and structured passivating contacts. The ink consists of neopentasilane oligomers in solvents and decomposes into amorphous silicon with a short anneal. By printing boron- and phosphorus-doped ink on silicon oxide, polycrystalline silicon on oxide (POLO) junctions for both p-type and n-type polarities (POLO²) are formed and the saturation current densities as low as 5 fA/cm2 are achieved for n+-POLO junctions. We perform a structured printing in interdigitated back contact (IBC) geometry achieving emitter and base fingers with an average finger height of up to 103 nm. The application of inkjet printing allows for a simplification of POLO and POLO2 solar cell processing. In particular, for POLO2-IBC cells, a lean process flow is facilitated.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hollemann2021cb,

title = {Firing stability of tube furnace-annealed n-type poly-Si on oxide junctions},

author = {C Hollemann and M Rienäcker and A Soeriyadi and C Madumelu and F Haase and J Krügener and B Hallam and R Brendel and R Peibst},

doi = {10.1002/pip.3459},

year  = {2021},

date = {2021-08-22},

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

abstract = {Stability of the passivation quality of poly-Si on oxide junctions against the conventional mainstream high-temperature screen-print firing processes is highly desirable and also expected since the poly-Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities (J0) and interface state densities (Dit) of symmetrical samples with n-type poly-Si contacts before and after firing. Samples without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The Dit values are (3 ± 0.2) × 1011 and (8 ± 2) × 1011 eV/cm2 when fired at 620°C and 900°C, respectively. The activation energy in an Arrhenius fit of Dit versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from SiH bonds at the poly-Si/SiOx interface is not the root cause of depassivation. Postfiring annealing at 425°C can improve the passivation again. Samples with SiNx capping layers show an increase in J0 up to about 100 fA/cm2 by firing, which can be attributed to blistering and is not reversed by annealing at 425°C. On the other hand, blistering does not occur in poly-Si samples capped with AlOx layers or AlOx/SiNy stacks, and J0 values of 2–5 fA/cm2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J0 and Dit: thermal stress at the SiOz interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.},

keywords = {},

pubstate = {forthcoming},

tppubtype = {article}

}

@article{Bayerl2021,

title = {Contacting a single nanometer-sized pinhole in the interfacial oxide of a poly-silicon on oxide (POLO) solar cell junction},

author = {P Bayerl and N Folchert and J Bayer and M Dzinnik and C Hollemann and R Brendel and R Peibst and R J Haug},

doi = {10.1002/pip.3417},

year  = {2021},

date = {2021-08-01},

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

volume = {29},

number = {8},

pages = {936-942},

abstract = {The electrical current through poly-Si on oxide (POLO) solar cells is mediated by tunneling and by nanometer-sized pinholes in the interfacial oxide. To distinguish the two processes, a POLO junction with a measured pinhole density of 1 × 107 cm−2 is contacted by different contact areas ranging from 1 μm2 to 2.5 × 105 μm2, and the temperature-dependent current–voltage curves are measured for the different devices. Model regressions to the measured curves, their temperature dependence, and the quantized value of contact resistances indicate average numbers of pinholes per device corresponding to the expected pinhole density. For the small contacts, the different transport processes can be studied separately, which facilitates further improvements in respect to the present-day POLO junctions. Single-pinhole transport is found for one of the contacts with an area of 1 μm2. Random telegraph noise observed for this device in the current–voltage characteristics shows a high sensitivity to single charges.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wehmeier2021,

title = {Kinetics of the Light and Elevated Temperature Induced Degradation and Regeneration of Quasi-Monocrystalline Silicon Solar Cells},

author = {N Wehmeier and G Fischer and S Herlufsen and F Wolny and M Wagner and K Bothe and M Müller},

doi = {10.1109/JPHOTOV.2021.3066239},

issn = {2156-3403},

year  = {2021},

date = {2021-07-01},

journal = {IEEE Journal of Photovoltaics},

volume = {11},

number = {4},

pages = {890-896},

abstract = {We investigate the degradation and regeneration behavior of quasi-monocrystalline silicon passivated emitter and rear cells under illumination at elevated temperatures. The decrease and increase of the solar cell efficiencies over time is accelerated under increased temperature or illumination intensity. We examine the defect activation kinetics and determine rate constants both for the degradation and regeneration. We apply temperatures in the range of 37–140 °C and illumination intensities in the range of 0.1–1.4 suns. These conditions typically occur when operating solar modules in the field. The rate constants are strongly increased with increasing temperature and increasing illumination intensity. We perform multiple regressions fits of the degradation and regeneration data with different approaches for the illumination intensity dependence. A linear illumination intensity dependence on the rates of degradation and regeneration is found. Activation energies for the degradation and regeneration of (0.89 ± 0.04) eV and (1.07 ± 0.07) eV, respectively, are extracted that allow for identification of the defect activation and deactivation mechanisms.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{McMahon2021,

title = {Homogenous Voltage-Matched Strings Using Three-Terminal Tandem Solar Cells: Fundamentals and End Losses},

author = {W E McMahon and H Schulte-Huxel and J Buencuerpo and J F Geisz and M S Young and T R Klein and A C Tamboli and E L Warren},

doi = {10.1109/JPHOTOV.2021.3068325},

year  = {2021},

date = {2021-07-01},

journal = {IEEE Journal of Photovoltaics},

volume = {11},

number = {4},

pages = {1078-1086},

abstract = {Strings constructed from three-terminal tandem (3TT) solar cells offer the performance benefits of voltage-matching (which reduces sensitivity to spectral variation), but without the subcell voltage isolation required by four-terminal cells. However, the circuitry for a 3TT string can become complex, making circuit analysis more challenging. Here, we illustrate the essential features of “homogenous” voltage-matched (VM) 3TT strings, for which all 3TT cells in the string are nominally identical (with the same design/doping sequence, such that they can be fabricated on the same manufacturing line). Several representative VM string configurations are explicitly considered, and used to describe the general construction of string I(V) curves. End losses intrinsic to these strings are discussed in detail, along with mitigation strategies to minimize their impact. Our analysis agrees with experimental results for eight-cell strings constructed from GaInP/GaAs 3TT devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Winter2021b,

title = {Carrier Lifetime Degradation and Regeneration in Gallium- and Boron-Doped Monocrystalline Silicon Materials},

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

doi = {10.1109/JPHOTOV.2021.3070474},

year  = {2021},

date = {2021-07-01},

journal = {IEEE Journal of Photovoltaics},

volume = {11},

number = {4},

pages = {866-872},

abstract = {In this article, carrier lifetime degradation phenomena on fired gallium-doped Czochralski-grown silicon (Cz-Si:Ga) and boron-doped float-zone silicon (FZ-Si:B) are observed. We examine lifetime degradation and regeneration as a function of illumination intensity and temperature and observe qualitatively similar degradation effects in both material classes, which are triggered by a fast-firing high-temperature step. Charge carrier injection, e.g., through illumination, is required to activate the defects responsible for degradation. The extent of degradation increases with increasing temperature, which is untypical for degradation effects reported before. Despite different degradation time constants are measured for Cz-Si:Ga and FZ-Si:B, the activation energies are for both materials in the narrow range (0.58±0.04) eV . The extracted activation energy is quite different compared with other degradation effects in silicon, suggesting a novel defect formation mechanism. Since the lifetime degradation is triggered by the fast-firing of the silicon wafers during the presence of a hydrogen-rich dielectric at the surface, the involvement of hydrogen in the defect reaction is very likely. During prolonged illumination at elevated temperature (135 °C), we observe a permanent regeneration of the lifetime, whereas at temperatures close to room temperature (36 °C), the defect deactivation is only temporary.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Min2021,

title = {Impact of Local Back-Surface-Field Thickness Variation on Performance of PERC Solar Cells},

author = {B Min and M Müller and B Wolpensinger and G Fischer and P Palinginis and D H Neuhaus and R Brendel},

doi = {10.1109/JPHOTOV.2021.3068603},

issn = {2156-3403},

year  = {2021},

date = {2021-07-01},

journal = {IEEE Journal of Photovoltaics},

volume = {11},

number = {4},

pages = {908-913},

abstract = {This article investigates the impact of the back-surface-field (BSF) thickness variation within a local aluminum contact on the performance of passivated emitter and rear contact solar cells. A significant difference of BSF thickness between contact endings and the center of dash-shaped contacts is verified experimentally by a comprehensive statistical analysis using scanning electron microscopy. The impact of local BSF thickness differences on the cell performance is studied with 3-D technology computer-aided design (TCAD) device simulations. Several device parameters such as BSF thicknesses, the doping concentration in the BSF profile at rear contacts, or the metallized area fraction at the cell rear side are varied. Our simulation study shows that the open-circuit voltage is mainly affected by locally reduced BSF thicknesses, resulting in an efficiency loss up to 0.14%$_abs$ or 0.84%$_abs$, respectively, if an area fraction of 1% or 20% within a local contact has reduced BSF thicknesses. This effect can be minimized either by reducing the metallized area fraction at the cell rear side or by increasing the doping concentration in the BSF profile at aluminum rear contacts. In addition, we demonstrate that the 3-D simulations can be approximated with 2-D simulations by applying a single doping profile with an average BSF thickness, calculated with the harmonic mean.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}