@misc{Ohrdes2020b,

title = {Wind-Solar-Wärmepumpen-Quartier – Erneuerbar betriebene Wärmepumpen zur Minimierung des Primärenergiebedarfs},

author = {T Ohrdes and M Knoop and E Schneider and A-K Fries and O Bast and L Franzen and J Behnisch},

year  = {2020},

date = {2020-02-14},

address = {Nordhausen, Germany},

note = {3. Regenerative Energietechnik Konferenz (RET.Con)},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Mercker2020,

title = {Simulationsstudie zum Potenzial netzdienlicher Betriebsweisen von Biomasse-Einzelraumfeuerstätten in TRNSYS - Methodik, Randbedingungen und Modelle},

author = {O Mercker and P Pärisch and D Büchner},

year  = {2020},

date = {2020-02-13},

address = {Nordhausen, Germany},

note = {3. Regenerative Energietechnik Konferenz (RET.Con)},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{VanSant2019b,

title = {Performance Comparison of III-V//Si Tandem Solar Cells in the Three-Terminal Configuration},

author = {K VanSant and E Warren and M Rienäcker and H Schulte-Huxel and R Peibst and J Geisz and P Stradins and A Tamboli},

year  = {2019},

date = {2019-12-04},

address = {Boston, USA},

abstract = {Multi-junction solar cells are a key pathway towards achieving higher photovoltaic efficiencies.The theoretical efficiency limit of a single-junction (1J) Si solar cell is 29.6%1, whereas efficiencies >32% have already been achieved for 1J III-V top cells stacked on Si bottom cells in both the two terminal (2T) and four terminal (4T) configurations.2,3 We will present a third path towards achieving efficiencies >32% with mechanically-stacked III-V-on-Si (III-V//Si) tandem solar cells using a three terminal (3T) configuration. The typical tandem device architectures either connect the sub-cells in series in a 2T configuration, or operate the stacked sub-cells independently, which requires four terminals (4T). Both configurations, however, have considerable drawbacks. The 2T configuration requires that the sub-cells are current matched to operate efficiently and so this narrowly constrains the choice of the sub-cell materials. The 4T configuration does not require sub-cell current matching but this design prohibits the possibility of monolithic growth and necessitates the inclusion of gridlines or a lateral conduction layer at the back of the top cell which reduces the transmission of light to the bottom cell.4The 3T configuration is a hybrid approach devised to address the constraints of the other two. The additional contact associated with the interdigitated back contact (IBC) Si bottom cell enables extraction or injection of current which circumvents the need for current matching between the sub-cells. The 3T design does not require an intermediate grid and is potentially compatible with both mechanical stacking, if a transparent conductive adhesive (TCA) is used, or monolithic growth. Moreover, simulations predict that 3T tandem cells could achieve efficiencies over 32%, comparable to record 4T tandem cell efficiencies.3,4We have fabricated and measured 3T mechanically-stacked III-V-on-Si (III-V//Si) tandem solar cells and will present an overview of how a 3T tandem solar cell operates. We will compare the JV and QE characteristics of a GaInP//Si tandem cell to a GaAs//Si tandem cell and analyze how the performance between these two 3T tandem solar cells differ, depending on which sub-cell is current limiting.},

note = {2019 MRS Fall Meeting & Exhibit},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Whitehead2019,

title = {Optimizing the top cell absorbing layer thickness in 4T GaAs on Si tandem solar cells},

author = {R Whitehead and K VanSant and M Rienäcker and J Geisz and A Tamboli},

year  = {2019},

date = {2019-12-03},

address = {Boston, USA},

abstract = {One method to improve silicon solar cell efficiency is to stack a silicon cell beneath a wide-bandgap top cell. To improve the overall tandem cell efficiency from that of silicon alone, the top cell material should have a higher spectral efficiency than silicon for the wavelengths of light within the top cell’s bandgap. GaAs is currently the material with the highest recorded cell efficiency for a single junction cell, at 29.1% efficiency. GaAs also has a theoretical and realized spectral efficiency higher than that of silicon between the wavelengths of 360-860 nm. Our team was able to exploit these GaAs attributes to obtain a record efficiency of 32.8% for a mechanically-stacked rear heterojunction (RHJ) GaAs-on-Si (GaAs//Si) tandem cell designed to operate in the 4-terminal (4T) (i.e. optically coupled but electrically independent) configuration. The purpose of this study is to further optimize the GaAs emitter layer thickness to maximize the efficiency of the 4T GaAs//Si tandem cells. Our record 4T GaAs//Si tandem solar cell was achieved using a 2 μm GaAs emitter layer but subsequent optical modeling of the 4T GaAs//Si tandem solar cells suggests that a slightly thicker emitter could potentially lead to even better top cell efficiencies. In addition, NREL began a collaboration with ISFH that provides high-efficiency interdigitated back contact (IBC) solar cells that could further improve the tandem cell efficiencies, when used as the Si bottom cell in the 4T GaAs//Si cell. Our un-certified current-voltage (I-V) results show an efficiency increase of 0.43% (absolute) by increasing the emitter thickness from 2.0 μm to 2.8 μm. The tandem cells are currently pending cell certification but the results for the GaAs//Si tandem cell with an emitter thickness of 2.8 μm is expected to be >32% and could potentially exceed the existing record efficiency. We will present the results of modeling the GaAs emitter thickness using modified Hovel equations that estimates the Jsc, based upon light absorption and carrier recombination. We will compare these modeled predictions to the NREL-certified I-V and external quantum efficiency (EQE) results obtained from 4T GaAs//Si tandem cells fabricated with absorber layer thicknesses varying from 1.5 to 3.5 μm. We will also compare the performance of our 4T GaAs//Si tandem cells to the record 4T GaAs//Si tandem cell efficiency of 32.8%.},

note = {2019 MRS Fall Meeting & Exhibit},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Kajari-Schroder2019b,

title = {High-Quality Kerfless Wafers from the Porous Silicon Layer Transfer Process},

author = {S Kajari-Schroder and C Gemmel and J Hensen and J Strey and R Brendel},

year  = {2019},

date = {2019-12-02},

address = {Boston, USA},

abstract = {Silicon wafers constitute a significant cost factor in solar cell and module manufacturing. The porous silicon (PSI) layer transfer process is a kerfless wafering technique that allows for a drastically reduced material and energy consumption per wafer and thus has great potential to reduce the wafer cost. In this process, a thick, highly p-doped substrate is electrochemically porosified, reorganized at high temperature and used as a growth substrate for silicon epitaxy. The epitaxial layer can subsequently be lifted off and the substrate wafer is reused. Key requirements for the realization of this potential in PV industry are, amongst others, a high lift-off yield of the epitaxial wafers from the porosified growth substrate, a robust process sequence, and a high electronic quality at the level of wire-cut Cz wafers. Furthermore, the kerfless wafers should be readily usable in standard solar cell manufacturing equipment, providing drop-in replacement wafers for PV industry. Here, we summarize the recent progress demonstrating several of these key aspects: first, we show that the PSI process is robust with respect to a moderate variation of processing parameters. In high-volume production, it is desirable to use e.g. a typical range of growth substrate resistivities and to use an electrolyte for the porosification process for an extended time. Both conditions would lead to a varying porosity of the growth substrate. We simulate this by a controlled variation of etching parameters, which also results in a variation of porosities in the growth substrate. We find a) that the lifetime of the PSI wafers is independent of the growth substrate separation layer porosities and b) that a reasonable process window in terms of the etching current density can be found. Second, we discuss the statistical evaluation of a large set of epitaxial runs with respect to the process yield: we are able to achieve lift-off of 59 out of 62 PSI wafers, which demonstrates a lift-off yield of the PSI process within our rigorously defined process window of at least 88 % with an error probability of 5 %. Finally, we show that high minority carrier lifetimes of up to 4.3 ms on n-type PSI wafers are achievable right after the epitaxy process, and that these lifetimes can be increased either by phosphorous diffusion gettering or by gettering with a n-type polysilicon on oxide (POLO) junction to up to 8 ms. With this, the PSI wafers are on par with standard PV wafers regarding the electronic quality.},

note = {2019 MRS Fall Meeting & Exhibit},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Reineke-Koch2019,

title = {Überhitzungsschutz für Solarkollektoren – neue Lösungswege},

author = {R Reineke-Koch},

year  = {2019},

date = {2019-11-29},

address = {Bern, Switzerland},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Schulte-Huxel2019d,

title = {Interconnect-shingling: Maximizing the active module area to surpass 22% module efficiency with bifacial contacted solar cells},

author = {H Schulte-Huxel},

year  = {2019},

date = {2019-11-07},

address = {Xi'an, China},

note = {29th International PV Science and Engineering Conference (PVSEC-29)},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Dullweber2019,

title = {PERC+POLO solar cells minimizing carrier recombination at the Ag front contact with simulated efficiency potential up to 23.8%},

author = {T Dullweber and M Stöhr and C Kruse and F Haase and M Rudolph and B Beier and P Jaeger and V Mertens and R Peibst and R Brendel},

year  = {2019},

date = {2019-11-06},

address = {Xi'an, China},

note = {29th International PV Science and Engineering Conference (PVSEC-29)},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Giovannetti2019c,

title = {Experimental Investigations on Photovoltaic-Thermal Arrays Designed for the Use as Heat Pump Source},

author = {F Giovannetti},

year  = {2019},

date = {2019-11-04},

address = {Santiago, Chile},

note = {ISES Solar World Congress and IEA Solar Heating and Cooling (SHC) Conference},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}

@misc{Giovannetti2019d,

title = {Improved flat plate collector with heat pipes for overheating prevention in solar thermal systems},

author = {F Giovannetti},

year  = {2019},

date = {2019-11-04},

address = {Santiago, Chile},

note = {ISES Solar World Congress and IEA Solar Heating and Cooling (SHC) Conference},

keywords = {},

pubstate = {published},

tppubtype = {presentation}

}