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Purpose: KEAP1 and NFE2L2 mutations are associated with impaired prognosis in a variety of cancers and with squamous cell carcinoma formation in non–small cell lung cancer (NSCLC). However, little is known about frequency, histology dependence, molecular and clinical presentation as well as response to systemic treatment in NSCLC.Experimental Design: Tumor tissue of 1,391 patients with NSCLC was analyzed using next-generation sequencing (NGS). Clinical and pathologic characteristics, survival, and treatment outcome of patients with KEAP1 or NFE2L2 mutations were assessed.Results: KEAP1 mutations occurred with a frequency of 11.3% (n = 157) and NFE2L2 mutations with a frequency of 3.5% (n = 49) in NSCLC patients. In the vast majority of patients, both mutations did not occur simultaneously. KEAP1 mutations were found mainly in adenocarcinoma (AD; 72%), while NFE2L2 mutations were more common in squamous cell carcinoma (LSCC; 59%). KEAP1 mutations were spread over the whole protein, whereas NFE2L2 mutations were clustered in specific hotspot regions. In over 80% of the patients both mutations co-occurred with other cancer-related mutations, among them also targetable aberrations like activating EGFR mutations or MET amplification. Both patient groups showed different patterns of metastases, stage distribution and performance state. No patient with KEAP1 mutation had a response on systemic treatment in first-, second-, or third-line setting. Of NFE2L2-mutated patients, none responded to second- or third-line therapy.Conclusions: KEAP1- and NFE2L2-mutated NSCLC patients represent a highly heterogeneous patient cohort. Both are associated with different histologies and usually are found together with other cancer-related, partly targetable, genetic aberrations. In addition, both markers seem to be predictive for chemotherapy resistance. Clin Cancer Res; 24(13); 3087–96. ©2018 AACR.

Supplemental Table 1-7 Supplemental Table 1: Diagnostic panels used for Next-generation sequencing (NGS) Supplemental Table 2: KEAP1 mutations Supplemental Table 3: NFE2L2 mutations Supplemental Table 4: Co-aberrations of KEAP1 Supplemental Table 5: Co-aberrations of NFE2L2 Supplemental Table 6: Distribution on FISH finding depending on histology Supplemental Table 7: Therapeutic outcome of patients receiving systemic therapy.

Main characteristics of the control group.

During embryogenesis, the genome shifts from transcriptionally quiescent to extensively active in a process known as Zygotic Genome Activation (ZGA). In Drosophila, the pioneer factor Zelda is known to be essential for the progression of development; still, it regulates the activation of only a small subset of genes at ZGA. However, thousands of genes do not require Zelda, suggesting that other mechanisms exist. By conducting GRO-seq, HiC and ChIP-seq in Drosophila embryos, we demonstrate that up to 65% of zygotically activated genes are enriched for the histone variant H2A.Z. H2A.Z enrichment precedes ZGA and RNA Polymerase II loading onto chromatin. In vivo knockdown of maternally contributed Domino, a histone chaperone and ATPase, reduces H2A.Z deposition at transcription start sites, causes global downregulation of housekeeping genes at ZGA, and compromises the establishment of the 3D chromatin structure. We infer that H2A.Z is essential for the de novo establishment of transcriptional programs during ZGA via chromatin reorganization., Nature Communications, 12 (1), ISSN:2041-1723

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2022 are reviewed. An appendix describing temporary electrical contacting of large-area solar cells approaches and terminology is also included.

For measuring the current-voltage (I-V) characteristics of busbarless solar cells, there is a certain degree of freedom in the choice of the contacting configuration as none has been defined as standard yet. This leads to the question of how the energy conversion efficiency of a busbarless solar cell should be specified when there are different measured values for it and poses the risk of misinterpreting cell measurements: Designing the measurement system for highest cell efficiencies for example may be tempting but can lead to cell results disassociated from later module performance and reduced cell-to-module power factors. The loss in module efficiency can thereby significantly exceed 5 %rel. It is therefore recommended to always adapt the contacting system to the module interconnection to yield meaningful I-V results in cell measurements. As a remedy for non-adapted measurement conditions, it is shown that I-V results can be converted from various cell measurement configurations to the module configuration. An analytical approach for the conversion of I-V results between measurement systems with different numbers of current contact bars as well as different shading properties is proposed. The approach is validated experimentally on busbarless cells over a large grid resistivity range. For three measurement systems with very different contacting schemes, the differences in fill factor and efficiency between the systems before correction clearly exceeded 10 %rel for high grid resistivities. After correction, good agreement in I-V characteristics within typical measurement uncertainties were shown. Limitations to the analytical approach associated with finger interruptions are identified and discussed.

Summary The production of alternative RNA variants contributes to the tissue-specific regulation of gene expression. In the animal nervous system, a systematic shift toward distal sites of transcription termination produces transcript signatures that are crucial for neuron development and function. Here, we report that, in Drosophila, the highly conserved protein ELAV globally regulates all sites of neuronal 3′ end processing and directly binds to proximal polyadenylation sites of target mRNAs in vivo. We uncover an endogenous strategy of functional gene rescue that safeguards neuronal RNA signatures in an ELAV loss-of-function context. When not directly repressed by ELAV, the transcript encoding the ELAV paralog FNE acquires a mini-exon, generating a new protein able to translocate to the nucleus and rescue ELAV-mediated alternative polyadenylation and alternative splicing. We propose that exon-activated functional rescue is a more widespread mechanism that ensures robustness of processes regulated by a hierarchy, rather than redundancy, of effectors.

The production of alternative RNA variants contributes to the tissue-specific regulation of gene expression. In the animal nervous system, a systematic shift towards distal sites of transcription termination produces transcript signatures that are crucial for neuron development and function. Here, we report that the highly conserved protein ELAV globally regulates all events of neuronal 3’end processing by directly binding to proximal polyadenylation sites of target mRNAs. We uncover an endogenous strategy of functional gene rescue that safeguards neuronal RNA signatures in a loss-of-function context. When not directly repressed by ELAV, the transcript encoding the ELAV paralogue FNE acquires a mini-exon, generating a new protein able to translocate to the nucleus and rescue neuronal 3’end processing. We propose that EXon-Activated functional Rescue is a more widespread mechanism that ensures robustness of processes regulated by a hierarchy, rather than redundancy, of effectors.

Purpose: KEAP1 and NFE2L2 mutations are associated with impaired prognosis in a variety of cancers and with squamous cell carcinoma formation in non–small cell lung cancer (NSCLC). However, little is known about frequency, histology dependence, molecular and clinical presentation as well as response to systemic treatment in NSCLC. Experimental Design: Tumor tissue of 1,391 patients with NSCLC was analyzed using next-generation sequencing (NGS). Clinical and pathologic characteristics, survival, and treatment outcome of patients with KEAP1 or NFE2L2 mutations were assessed. Results: KEAP1 mutations occurred with a frequency of 11.3% (n = 157) and NFE2L2 mutations with a frequency of 3.5% (n = 49) in NSCLC patients. In the vast majority of patients, both mutations did not occur simultaneously. KEAP1 mutations were found mainly in adenocarcinoma (AD; 72%), while NFE2L2 mutations were more common in squamous cell carcinoma (LSCC; 59%). KEAP1 mutations were spread over the whole protein, whereas NFE2L2 mutations were clustered in specific hotspot regions. In over 80% of the patients both mutations co-occurred with other cancer-related mutations, among them also targetable aberrations like activating EGFR mutations or MET amplification. Both patient groups showed different patterns of metastases, stage distribution and performance state. No patient with KEAP1 mutation had a response on systemic treatment in first-, second-, or third-line setting. Of NFE2L2-mutated patients, none responded to second- or third-line therapy. Conclusions: KEAP1- and NFE2L2-mutated NSCLC patients represent a highly heterogeneous patient cohort. Both are associated with different histologies and usually are found together with other cancer-related, partly targetable, genetic aberrations. In addition, both markers seem to be predictive for chemotherapy resistance. Clin Cancer Res; 24(13); 3087–96. ©2018 AACR.

Summary Due to the rapidly increasing scale and diversity of epigenomic data, modular and scalable analysis workflows are of wide interest. Here we present snakePipes, a workflow package for processing and downstream analysis of data from common epigenomic assays: ChIP-seq, RNA-seq, Bisulfite-seq, ATAC-seq, Hi-C and single-cell RNA-seq. snakePipes enables users to assemble variants of each workflow and to easily install and upgrade the underlying tools, via its simple command-line wrappers and yaml files. Availability and implementation snakePipes can be installed via conda: `conda install -c mpi-ie -c bioconda -c conda-forge snakePipes’. Source code (https://github.com/maxplanck-ie/snakepipes) and documentation (https://snakepipes.readthedocs.io/en/latest/) are available online. Supplementary information Supplementary data are available at Bioinformatics online.

The scale and diversity of epigenomics data has been rapidly increasing and ever more studies now present analyses of data from multiple epigenomic techniques. Performing such integrative analysis is time-consuming, especially for exploratory research, since there are currently no pipelines available that allow fast processing of datasets from multiple epigenomic assays while also allow for flexibility in running or upgrading the workflows. Here we present a solution to this problem: snakePipes, which can process and perform downstream analysis of data from all common epigenomic techniques (ChIP-seq, RNA-seq, Bisulfite-seq, ATAC-seq, Hi-C and single-cell RNA-seq) in a single package. We demonstrate how snakePipes can simplify integrative analysis by reproducing and extending the results from a recently published large-scale epigenomics study with a few simple commands. snakePipes are available under an open-source license at https://github.com/maxplanck-ie/snakepipes.

In this study, we present detailed theoretical and experimental investigations on full-area alloying from screen-printed aluminum pastes on silicon surfaces for solar cell applications. We introduce a simple analytical model for the description of the alloying process derived from existing models for evaporated Al layers, which we adapt to printed Al pastes. Thereby, we particularly account for the recrystallization of Si within the paste particles, which we refer to as parasitic Si recrystallization. Applying our model, we demonstrate good accordance of calculated with measured eutectic layer thicknesses. We show that the model can be versatilely used to investigate screen-printed Al-alloyed contacts in detail: We demonstrate that the latent heat of the Al paste significantly influences the alloying process. Thus, the effective peak temperature of the alloying process can be several 100 °C below the set peak temperature of the firing furnace. By combining calculations of the effective peak temperature with measurements of the Al doping concentration, we determine a parameterization of the solid solubility of Al in Si down to the eutectic temperature of 577 °C. Our investigations therefore provide improved understanding of alloying from printed Al pastes and enable the specific optimization of Al-alloyed contacts.

We present a detailed study on aluminum-boron codoping of silicon by alloying from screen-printed aluminum pastes containing boron additives (Al–B pastes). We derive an analytical model for the formation of the Al–B acceptor profiles by quantitatively describing (i) the composition of the Al–B–Si melt and (ii) the incorporation of Al and B acceptor atoms into the recrystallizing Si lattice. We show that measured Al–B dopant profiles can be excellently described by this model, which therefore offers a straightforward method for the comprehensive investigation of alloying from Al–B pastes. The formation of a characteristic kink in the Al–B dopant profile curve can thus be ascribed to the exhaustion of the B additive dissolution during alloying. By intentionally adding elemental B powder to an Al paste, we demonstrate that only a low percentage of the B powder actually dissolves into the melt. We show that this incomplete dissolution of the B additive strongly affects the recombination characteristics of Al–B–p+ regions and, thus, is an important element of alloying from Al–B pastes. This study therefore provides improved understanding of aluminum-boron codoping of silicon. Copyright © 2015 John Wiley & Sons, Ltd.

Reducing wafer thickness while increasing power conversion efficiency is the most effective way to reduce cost per Watt of a silicon photovoltaic module. Within the European project 20 percent efficiency on less than 100-mu m-thick, industrially feasible crystalline silicon solar cells ("20pl mu s"), we study the whole process chain for thin wafers, from wafering to module integration and life-cycle analysis. We investigate three different solar cell fabrication routes, categorized according to the temperature of the junction formation process and the wafer doping type: p-type silicon high temperature, n-type silicon high temperature and n-type silicon low temperature. For each route, an efficiency of 19.5% or greater is achieved on wafers less than 100 mu m thick, with a maximum efficiency of 21.1% on an 80-mu m-thick wafer. The n-type high temperature route is then transferred to a pilot production line, and a median solar cell efficiency of 20.0% is demonstrated on 100-mu m-thick wafers. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We investigate the application of nickel-plated front contacts to front and rear emitter silicon solar cells. We compare identically processed p - and n -type Si solar cells featuring (i) a homogeneous phosphorus-diffused n + front, acting as emitter or front surface field and (ii) a full-area aluminum-alloyed p + rear, acting as back surface field or rear emitter. This results in an n + pp + front emitter and an n + np + rear emitter solar cell structure, respectively. We show that the contact annealing temperature for the thermal formation of the nickel silicide (NiSi x ) after the electroless Ni plating has a significant influence on the NiSi x layer thickness. Increasing the temperature from 300 to 450 °C shifts the average thickness to higher values and augments deep NiSi x spikes. The intensified penetration of the n + front by the NiSi x spikes leads to a strong degradation of the front emitter p -type Si solar cell performances due to (i) decreased shunt resistances and (ii) the contamination of the emitter space charge region. We demonstrate that the rear emitter n -type Si solar cells, in contrast, are explicitly more stable. Therefore, by applying n - instead of p -type Si as base material, an improved stability against the thermal Ni contact formation can be easily realized without significant changes in the solar cell fabrication process.

We present a detailed study on aluminum-boron doping profiles formed in silicon by alloying from screen-printed aluminum pastes containing boron additives. We show that an increase in the effective peak temperature Tpeak,eff (determined from phase diagram calculations) of the alloying process leads to higher concentrations of both Al and B atoms within the alloyed p+ region, resulting in (i) higher potential barriers for electrons, but also (ii) increased densities of recombination-active Al defects. While the improved potential barrier predominates for Tpeak,eff ≲ 770 °C, the increased defect density prevails for Tpeak,eff ≲ 800 °C, thus defining an optimal effective peak temperature. Furthermore, we show that, by increasing the amount of elemental B added to the paste, the acceptor concentration can be increased without affecting the defect density. Therefore, the optimal printing and firing conditions comprise high B amounts and low, adapted effective peak temperatures. For a B content of 0.9 wt% and Tpeak,eff = 765 °C, we have achieved a saturation current density of 253 fA/cm2, corresponding to an implied open-circuit voltage of 665 mV, which demonstrates the high potential of B additives within Al pastes to further improve the efficiency of Si solar cells with Al-alloyed p+ rear.

The firing of screen-printed aluminum pastes is well established for the formation of a back surface field (BSF) and back contacts since many years in silicon solar cell fabrication. In this paper we investigate the electrical and microstructural properties of Al-alloyed contacts and their layer system, consisting of (i) the Al-doped p+-layer (2–14 μm), the eutectic layer (1–15 μm) and the layer of paste residuals (20–100 μm). We show the influence of process parameters like the amount of printed paste, the alloying time and the peak temperature. Special emphasis is devoted to the properties of small alloyed screen-printed aluminum structures for the formation of local aluminum back contacts. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electrochemical capacitance voltage (ECV) and conductivity measurements have been applied to characterize the samples. A simple model is qualitatively augmented to describe all effects occurring in a technical alloying process. For example, for increasing aluminum amounts, a saturation of the p+-layer thickness was found in the range of 10 mg/cm2. For small screen-printed structures, the p+-layer is formed very homogenously and with a greater thickness compared to samples with a full-area Al metallization, which have been processed with similar alloying conditions. For the eutectic layer a high electrical conductivity of about 16×106 S/m, only 2–3 times below that of pure aluminum has been determined. This is advantageous for the lateral conductivity especially for high paste amounts and small structures, which feature a relatively thick eutectic layer.

We present a comprehensive study on the rear contact formation of rear surface-passivated silicon solar cells by full-area screen printing and alloying of aluminum pastes on the locally opened passivation layer. We show that the point contact distance has a significant influence on the local alloying process for the contact formation resulting in different structural and electrical contact properties when applying conventional Al pastes. Increasing the distance leads to 1) high contact depths resulting in an enlargement of the contact area and 2) severely reduced thicknesses of the Al-doped p+ regions in the contact points, leading to a strong increase in recombination within the contact points. This inadequate contact formation can be directly linked to the deficiently low percentage of silicon that dissolves into the Al-Si melt during alloying. We demonstrate that by intentionally adding Si to the Al paste, the contact point geometry can be significantly improved and particularly becomes independent of the contact distance. Further investigations on the internal reflectance and the specific resistivity of the rear contact suggest an upper limit for the Si content added to the Al paste. In summary, we present a simple way to significantly improve the rear contact formation of rear surface-passivated silicon solar cells.

Surface-passivated and surface-unpassivated aluminum-alloyed p+-layers are characterized. By varying the firing conditions and the thickness of the screen-printed aluminum paste, different sheet resistances Rsh of the p+-layer were fabricated. The emitter saturation current density J0e plotted versus Rsh follows distinctly different trends for the passivated and unpassivated samples. An aluminum paste with a boron additive achieves a much higher doping concentration and a lower sheet resistance but nevertheless follows the same J0e curves as the pure Al paste. The aluminum p+-layer was quantitatively analyzed with microphotoluminescence and Fano-Raman measurements. The latter shows an increased defect recombination at the interface between the p+-layer and the moderately doped Si bulk. The lower Shockley-Read-Hall lifetime in this region can be attributed to a high defect concentration in the most highly doped layer, represents an impediment to the reduction of J0e for Al-doped emitter regions, and needs to be optimized in future investigations.

The amount of incomplete ionization of aluminum-doped silicon is measured at room temperature by comparing electrochemical capacitance-voltage measurements with micro Raman spectroscopy. It is shown that commonly used parameterizations significantly underestimate the effect of incomplete ionization in Al doped Si. Based on the experimental data, we propose new parameter values for the parameterization of incomplete ionization given in Altermatt et al., J. Appl. Phys. 100, 113715 (2006). Using these new values, the saturation current density J0,p+ of the Al-alloyed region of a standard silicon solar cell is determined by means of numerical device modeling. It is shown that the parameterization influences J0,p+ significantly. Additionally, the weakening effect of incomplete ionization on band gap narrowing (BGN) should be taken into account in modeling that aims to predict device behavior after changes made to the Al-alloyed region.

We present a detailed study on surface-passivated screen-printed aluminium-alloyed emitters for back junction n-type silicon solar cells. We investigated (i) two different commercially available aluminium pastes and (ii) two passivation layers both well suited for highly doped p+ silicon: plasma-enhanced-chemical-vapour-deposited amorphous silicon (a-Si) and atomic-layer-deposited aluminium oxide (Al2O3). We show that for the formation of a homogeneous, non-shunted emitter, a careful choice of the alloying conditions is essential. Moreover, for a most effective surface passivation, low emitter thicknesses have to be used. Combining these two aspects, we have achieved extraordinary high implied open-circuit voltages of 673 mV for a-Si- and 685 mV for Al2O3-passivated Al-alloyed emitters, corresponding to emitter saturation current densities of 128 and 55 fA/cm2, respectively.

We present a detailed study on alloying from screen-printed aluminum pastes containing boron additives (Al-B pastes) to further enhance the efficiency of p- and n-type silicon solar cells with an Al-alloyed back-surface field and rear emitter, respectively. Due to the high B solubility in Si, the additional incorporation of B atoms as acceptors into the Al-alloyed p+ region-referred to as Al-B codoping of Si-provides improved shielding of electrons from the recombination-active surface. Thus, alloying from Al-B pastes allows for significantly thinner p + regions and leads to a considerable reduction of the p + saturation current densities. By comparing surface-passivated p+ regions alloyed from Al-B pastes or conventional Al pastes with each other, we show that a highly recombination-active defect limits the minority carrier lifetime in these p+ regions. We demonstrate that the acceptor concentration profiles of the p+ regions can easily be modified by adding different amounts of aluminum diboride or boron trioxide as B sources to the Al pastes.

We present a detailed analysis on the efficiency potential of n -type silicon solar cells with aluminum-doped rear p + emitter for industrial applications by means of 2-D and 3-D numerical simulations. Thereby, this study examines successively three different regions of the solar cell. First, the front side is investigated by discussing the influence of different uniform and selective front surface fields (FSFs). Additionally, the case of omitting a full-area FSF and only applying local heavily doped areas below the front contacts is analyzed. Second, we look into the base and how doping concentrations and finger distance variations influence each other. Finally, the back side of this solar cell concept is examined by 3-D simulations, demonstrating the effect of a surface-passivated and locally contacted aluminum-doped rear p + emitter on the cell performance. As a result of our considerations, we have determined an efficiency potential for this $n{+}np + cell concept close to 21%.

Broad range injection-dependent carrier lifetime measurements in crystalline silicon are most relevant for both defect level spectroscopy, and for the investigation of recombination properties of novel solar cell technologies. The approach presented in this paper combines a determination of the effective carrier lifetime via time-dependent (quasi-steady-state) photoluminescence with a steady-state photoluminescence lifetime scan over a broad range of excess carrier densities. Thereby, the power of a virtually artifact-free time-domain approach is combined with the high sensitivity of steady-state photoluminescence at extremely low injection conditions. Time-dependent fluctuations of dark photocurrent measurements are identified as the essential source of uncertainty under such low injection. A measurement design which eliminates this source of uncertainty is presented and tested. Lifetime measurements at excess carrier densities as low as 10 8 cm −3 are shown in detail.

The passivation mechanisms and qualities of Al2O3, SiNx, SiO2 and a-Si:H( i ) on p - and n -type silicon are investigated by quasi-steady-state photoluminescence measurements. This technique allows effective lifetime measurements in an extremely large injection range between 1010 cm-3 and 1017 cm-3. The measurements are discussed focusing on injections below 1012 cm-3 in order to determine the most effective passivation layer for solar cells arranged for indoor applications. Fixed negative charges in the passivation layer cause field-effect passivation due to band bending leading to either accumulation or inversion at the passivation layer/silicon interface. Accumulation causes a stable passivation quality at low level injection. Inversion leads to effective lifetime losses similar to the losses in the space charge region. On p -type silicon the most effective surface passivation at low injections is provided by Al2O3 or a-Si:H( i ). The n -type silicon samples passivated with a-Si:H( i ) show the best effective lifetimes. SiNx and SiO2 show lifetimes one order of magnitude below a-Si:H( i ). Al2O3 on n -type is the most effective passivation at high injections around 1015 cm-3. Due to inversion losses at low level injections the passivation quality decreases more than two orders of magnitude for injections around 1010 cm-3.

We present a detailed study on the rear contact formation of rear-surface-passivated silicon solar cells by full-area screen printing and alloying of aluminum pastes on the locally opened passivation layer. We demonstrate that applying conventional Al pastes exhibits two main problems: (1) high contact depths leading to an enlargement of the contact area and (2) low thicknesses of the Al-doped p+ Si regions in the contact points resulting in poor electron shielding. We show that this inadequate contact formation can be directly linked to the deficiently low percentage of silicon that dissolves into the Al-Si melt during alloying. Thus, by intentionally adding silicon to the Al paste, we could significantly improve the contact geometry by reducing the contact depth and enlarging the Al-p+ thickness in the contact points, enabling a simple industrially feasible way for the rear contact formation of silicon solar cells.

In the first part of this paper we estimate the efficiency potential of crystalline silicon solar cells on conventionally pulled p-type boron-doped Czochralski-grown silicon with typical oxygen concentrations. Taking into account an industrial high-efficiency cell structure featuring fine-line metallization, shallow and well-passivated emitter and a rear surface structure with dielectric passivation and local laser-fired point contacts, the maximum achievable efficiency is around 20%. The main limitation of such a cell is due to the rather low bulk lifetime after light-induced degradation. Even when avoiding the metastable boronoxygen defect by using Gallium-doped or magnetic Cz-silicon, it has to be kept in mind that the detrimental impact of metal contaminations on p-type silicon is greater than on n-type silicon. A potential strategy to reduce this loss is the use of n-type silicon. Therefore, the second part of the paper discusses different architectures for solar cells on n-type silicon substrates and shows the latest results achieved at Fraunhofer ISE in this field.

In this study we present an advanced method for precise modeling of highly aluminum-doped p+ silicon, leading to excellent agreement of numerical and experimental data within a broad range. We analyze the influence of different recombination mechanisms on the saturation current densities of Al-doped Si surfaces for different Al profiles. Lateral doping inhomogeneities and the effect of incomplete ionization have been examined in detail. We demonstrate that incomplete ionization affects the profile characteristics significantly and, therefore, has to be accounted for in accurate modeling of highly Al-doped silicon.

We present a detailed study on the formation of full-area screen-printed aluminum-alloyed p+ emitters and back surface fields for n- and p-type silicon solar cells, respectively. We have investigated the structural properties of agglomerated Al-doped p+ Si regions which exhibit serious lateral thickness inhomogeneities. We refined an existing simple model based on wetting phenomena for the formation of agglomerated Al-p+ regions. According to the model, the thickness inhomogeneities are caused by the contraction of the Al-Si melt during alloying, leading to enhanced and decelerated Si recrystallization in the regions of melt accumulation and depletion, respectively. Furthermore, we demonstrate that the melt contraction can be delayed by carefully choosing adequate alloying conditions. In particular, agglomerations are avoided by increasing the printed Al paste amount or decreasing the peak temperature time or peak temperature, thus enabling a more flexible fabrication of Si solar cells with Al-alloyed rear side.

We present a detailed study on accurate modeling of highly aluminum-doped p+ silicon. We have analyzed the influence of defect recombination and the effect of incomplete ionization on the saturation current densities of Al-p+ regions featuring different Al doping profiles. Very good agreement within a broad range of experimental data has been obtained. We demonstrate that incomplete ionization has a significant impact on the doping profile characteristics and, therefore, has to be accounted for in accurate modeling of highly aluminum-doped silicon.