Papers by Andreas Lambertz
Results in Physics, 2021
The extensive usage of X-ray spectroscopies in studying complex material systems is not only inte... more The extensive usage of X-ray spectroscopies in studying complex material systems is not only intended to reveal underlying mechanisms that govern physical phenomena, but also used in applied studies focused on an insightdriven performance improvement of a wide range of devices. However, the traditional analysis methods for X-ray spectroscopic data are rather time-consuming and sensitive to errors in data pre-processing (e.g., normalization or background subtraction). In this study, a method based on grey relational analysis, a multi-variable statistical method, is proposed to analyze and extract information from X-ray spectroscopic data. As a showcase, the valence bands of microcrystalline silicon suboxides probed by hard X-ray photoelectron spectroscopy (HAXPES) were investigated. The results obtained by the proposed method agree well with conventionally derived composition information (e.g., curve fit of Si 2p core level of the silicon suboxides). Furthermore, the uncertainty of chemical compositions derived by the proposed method is smaller than that of traditional analysis methods (e. g., the least square fit), when artificial linear functions are introduced to simulate the errors in data preprocessing. This suggests that the proposed method is capable of providing more reliable and accurate results, especially for data containing significant noise contributions or that is subject to inconsistent data pre-processing. Since the proposed method is less experience-driven and error-prone, it offers a novel approach for automate data analysis, which is of great interest for various applications, such as studying combinatorial material "libraries".
Impact of Periodicity of Inverted Pyramids on Anti-reflection and Light-trapping Properties in Silicon Heterojunction Solar Cells
Light, Energy and the Environment, 2017
The Impact of Reflectance Variation in Silicon Heterojunction Solar Cells and Modules on the Perception of Color Differences
IEEE Journal of Photovoltaics, 2021
The color produced by visible light that reflects from the photovoltaic modules can influence vis... more The color produced by visible light that reflects from the photovoltaic modules can influence visual aesthetics for colored photovoltaic applications, such as the building integrated photovoltaic and the vehicles integrated photovoltaic. How two colors lying close together can be perceived by the human eye is important for aesthetic design. In this article, we investigate the reflectance spectra variation caused by the variation of indium tin oxide thickness and incidence angle of sunlight based on the well-known silicon heterojunction solar cells and modules. By converting the reflectance spectra into the Delta E 2000 value, we quantify whether differences in color can be perceived. The colors are also predicted based on the standard red, green, and blue color space. The results show that the reflectance variation because of an ITO thickness deviation of 5 nm in SHJ solar cells leads to a perceptible color difference, which can be suppressed after encapsulation but is still percept...
Function Analysis of the Phosphine Gas Flow for n-Type Nanocrystalline Silicon Oxide Layer in Silicon Heterojunction Solar Cells
ACS Applied Energy Materials, 2021
Lambertz et al-2015-Progress in Photovoltaics Research and Applications
Totally twelve title compounds have been synthesized by Claisen-Schmidt condensation of (E)-methy... more Totally twelve title compounds have been synthesized by Claisen-Schmidt condensation of (E)-methyl 2-(2-(((1-acetylnaphthalen-2-yl)oxy)methyl)phenyl)-3-methoxy acrylate and substituted benzaldehydes in presence of catalytic quantity of LiOH.H 2 O catalyst under stirring in room temperature. The yields of the compounds are more than 92%. The synthesized titled compounds were characterized by their physical constants, IR, NMR and Mass spectral data. The spectral data such as infrared ν CO s-cis , s-trans , CO ester , NMR chemical shifts (δ, ppm) of H α , H β , C α , C β , CO of enone moiety, H βʹ and CO of acrylate moieties have been correlated with Hammett substituent constants, F and R parameters. The antimicrobial, antioxidant and insect antifeedant activities of all synthesized compounds have been evaluated using corresponding bacterial and fungal strains, DPPH radical scavenging and Disc diffusion bio-assay of 4 th instar larvae Achoea Janata L with castor-leaf discs.
Detailed Analysis of a-Si:H/μc-Si:H Tandem Solar Cell Characterization Data Using Numerical Simulation
We investigated the complex optoelelectronic processes taking place within silicon thin-film sola... more We investigated the complex optoelelectronic processes taking place within silicon thin-film solar cell devices by comparing experimental and simulated characteristics (external quantum efficiency, current voltage characteristic, overall reflection). To this end we measured, calibrated and optimized electrical and optical input parameters for the numerical device simulator ASA with experimental data, with which different silicon thin film solar cell types are reproduced consistently. We obtained a good correspondence between the experimental and simulated characteristics of a-Si:H/μc-Si:H tandem solar cells of various absorber thicknesses and on both Asahi Utype and Jülich ZnO substrates. Further we show that insight into not directly measurable properties like the spaceresolved absorptance, collection and losses is provided. Optical simulations show that the difference between tandem solar cells grown on Asahi U-type and Jülich ZnO substrate originates primarily from their optics. Using bias dependent EQE measurements combined with simulations we find that doped layers, except for the front p-layer, do not contribute to the photocurrent density. Simulated efficiency mapping for different combinations of a-Si:H and μc-Si:H absorber layer thicknesses predicts the highest efficiencies of 10.60% at 260 nm/1500 nm for Asahi U-type and 10.62% at 360 nm/850 nm for Jülich ZnO.
Light-induced performance of SHJ solar modules under 2000 h illumination
Solar Energy Materials and Solar Cells, 2022
Front contact optimization for rear-junction SHJ solar cells with ultra-thin n-type nanocrystalline silicon oxide
Solar Energy Materials and Solar Cells, 2020
Abstract In this work, ultra-thin n-type hydrogenated nanocrystalline silicon oxide [(nc-SiOx:H (... more Abstract In this work, ultra-thin n-type hydrogenated nanocrystalline silicon oxide [(nc-SiOx:H (n)] film was used to replace amorphous silicon [a-Si:H (n)] as electron transport layer (ETL) in rear-junction silicon heterojunction (SHJ) solar cell to reduce front parasitic absorption. The contact resistivity between the transparent conductive oxide (TCO) and ultra-thin ETL interface plays an important role on the cell performance. A nanocrystalline silicon (nc-Si:H) contact or seed layer was introduced in the solar cell with ultra-thin nc-SiOx:H and the impact of the nc-Si:H thickness on the cell performance was investigated. To demonstrate scalability, bifacial solar cells with 10 nm ETL were fabricated on the M2 (244 cm2) wafer. The best cell performance is obtained by the solar cell with 5 nm nc-SiOx:H (n) and 5 nm nc-Si:H (n) contact layer and it exhibits open-circuit voltage (Voc) of 738 mV, fill factor (FF) of 80.4%, short-circuit current density (Jsc) of 39.0 mA/cm2 and power conversion efficiency (η) of 23.1% on M2 wafer. Compared to the one with nc-SiOx:H (n), an increase of 3%abs of FF and 0.5%abs of η and lower front contact resistivity is demonstrated for the solar cells with nc-Si:H (n) / nc-SiOx:H (n) double layer, which is caused by the lower energy barrier for electrons, according to the band diagram calculated by the AFORS-HET simulator. A simulation on the solar cell optical and electrical losses was done by the Quokka 3 simulator and shows much lower electrical transport loss and a bit higher front surface transmission loss for the one with double layer than nc-SiOx:H (n) single layer.
Preparation and measurement of highly efficient a-Si:H single junction solar cells and the advantages of μ c-SiO x :H n -layers
Progress in Photovoltaics: Research and Applications, 2015
Reducing the optical losses and increasing the reflection while maintaining the function of doped... more Reducing the optical losses and increasing the reflection while maintaining the function of doped layers at the back contact in solar cells are important issues for many photovoltaic applications. One approach is to use doped microcrystalline silicon oxide (μc-SiOx:H) with lower optical absorption in the spectral range of interest (300 nm to 1100 nm). To investigate the advantages, we applied the μc-SiOx:H n-layers to a-Si:H single junction solar cells. We report on the comparison between amorphous silicon (a-Si:H) single junction solar cells with either μc-SiOx:H n-layers or non-alloyed silicon n-layers. The origin of the improved performance of a-Si:H single junction solar cells with the μc-SiOx:H n-layer is identified by distinguishing the contributions because of the increased transparency and the reduced refractive index of the μc-SiOx:H material. The solar cell parameters of a-Si:H solar cells with both types of n-layers were compared in the initial state and after 1000 h of light soaking in a series of solar cells with various absorber layer thicknesses. The measurement procedure for the determination of the solar cell performance is described in detail, and the measurement accuracy is evaluated and discussed. For an a-Si:H single junction solar cell with a μc-SiOx:H n-layer, a stabilized efficiency of 10.3% after 1000 h light soaking is demonstrated. Copyright © 2015 John Wiley & Sons, Ltd.
Development of P-Type µc-SiOx:H for Thin-Film Silicon Solar Cells on Sputtered ZnO:Al
Hydrogenated microcrystalline silicon oxide (μc-SiOx:H) was developed and implemented as a contac... more Hydrogenated microcrystalline silicon oxide (μc-SiOx:H) was developed and implemented as a contact layer in hydrogenated amorphous thin film silicon (a-Si:H) single junction solar cells. Higher transparency, sufficient electrical conductivity, low ohmic contact to sputtered ZnO:Al and tunable refractive index make p-type μc-SiOx:H a promising alternative to the commonly used p-type μc-Si:H contact layers. In this work p-type μc-SiOx:H layers were fabricated with a conductivity up to the order of 10-2 S/cm and over 60% Raman crystallinity. Furthermore, we present p-type μc-SiOx:H with a broad range over which the optical properties (band gap E04 and refractive index n) can be tuned (2.1 eV < E04 < 2.8 eV and 1.6 < n < 2.6) by adapting deposition parameters like CO2/SiH4 ratio in the gas mixture. a-Si:H solar cells were produced with an conversion efficiency improvement from 9.4 to 9.7% by using p-type μc-SiOx:H compared to standard p-type μc-Si:H contact layer.
A process for producing a solar cell and a solar cell
The invention relates to a solar cell having a first electrical contact layer on a substrate, and... more The invention relates to a solar cell having a first electrical contact layer on a substrate, and a pin structure on the first electrical contact layer, the p-layer is disposed on the first electrical contact layer and a second electrical contact layer on which the pin n-layer structure, wherein the i-type layer of the pin structure is microcrystalline marked by an n-doped layer having a total oxygen content of 10 to 25% and comprising two phases, a microcrystalline Si: H phase and an amorphous SiO A process for the preparation of the solar cell and the use of the solar cell is disclosed.
Microcrystalline silicon solar cells : relationship between material properties and device performance
Utilization of ultra-thin n-type Hydrogenated Nanocrystalline Silicon for Silicon Heterojunction Solar Cells
2021 IEEE 48th Photovoltaic Specialists Conference (PVSC), 2021
To optimize the electrical performance of silicon heterojunction solar cell devices, the electron... more To optimize the electrical performance of silicon heterojunction solar cell devices, the electronic properties and microstructure of n-type nc-Si:H were characterized and analyzed. It was found that higher conductivity and crystalline volume fraction (F<inf>c</inf>) of nc-Si:H can be obtained at lower silane gas fraction (f<inf>SiH4</inf>), lower power and higher phosphorous gas fraction (f<inf>PH3</inf>). In our case, there is a decline of the passivation for the devices with nc-Si:H after sputtering process. By increasing the phosphine flow fraction, the sputter damage can be reduced and 3%<inf>abs</inf> gain of FF as well as 0.7%<inf>abs</inf> gain of efficiency is reached compared with reference. The best solar cell exhibits the V<inf>oc</inf> of 733.3 mV, FF of 79.7%, J<inf>sc</inf> of 39.00 mA/cm<sup>2</sup> and η of 22.79% at the M2 size wafer.
Development of Doped Microcrystalline Silicon Oxide and its Application to Thin‑Film Silicon Solar Cells
The aim of the present study is the development of doped microcrystalline silicon oxide (µc‑SiOx:... more The aim of the present study is the development of doped microcrystalline silicon oxide (µc‑SiOx:H) alloys and its application in thin‑film silicon solar cells. The doped µc‑SiOx:H material was prepared from carbon dioxide (CO2), silane (SiH4), hydrogen (H2) gas mixtures using plasma enhanced chemical vapour deposition (PECVD) with process conditions which are fully compatible with the overall solar cell manufacturing processes. Doping was achieved by adding phosphine (PH3) or trimethyl boron B(CH3)3 to the process gas. Particular focus in the material development is to establish the relationship between the deposition process parameters and the material properties of doped µc‑SiOx:H such as optical band gap, refractive index, conductivity, and crystalline volume fraction. To understand the individual influences of the different structural phases of the composite material µc‑SiOx:H the link between the optoelectronic properties and the material structure as well as the material comp...
Low-resistivity p-type a-Si:H/AZO hole contact in high-efficiency silicon heterojunction solar cells
Applied Surface Science
How thin practical silicon heterojunction solar cells could be? Experimental study under one sun and under indoor illumination
Solar RRL
Achieving a high Short Circuit Current Density of 40.9 mA/cm² for Two-Side Contacted Silicon Heterojunction Solar Cells by using SiC-based Transparent Passivating Contacts
2021 IEEE 48th Photovoltaic Specialists Conference (PVSC)
A silicon heterojunction solar cell using silicon carbide as front contact is presented, which fe... more A silicon heterojunction solar cell using silicon carbide as front contact is presented, which features the main advantage of high transparency. To enhance this advantage, an optical loss analysis is performed. It is found that reflection losses play an important role for the solar cell, which can easily be reduced by applying an additional MgF2 coating. The deposition of the coating degrades the passivation quality of the contact but can be cured, eventually leading to a certified short circuit current density of 40.9 mA/cm² and efficiency of 23.99%. Afterwards, a roadmap to a theoretical efficiency of 25% is presented.
In order to compensate the insufficient conductance of heterojunction thin films, transparent con... more In order to compensate the insufficient conductance of heterojunction thin films, transparent conductive oxides (TCO) have been used for decades in both-sides contacted crystalline silicon heterojunction (SHJ) solar cells to provide lateral conduction for efficient carrier collection. In this work, we substitute the TCO layers by utilizing the lateral conduction of c-Si absorber, thereby enabling a TCO-free design. A series resistance of 0.32 Ωcm2 and a fill factor of 80.7% were measured for a TCO-free back-junction SHJ solar cell with a conventional finger pitch of 1.8 mm, thereby proving that relying on lateral conduction in the c-Si bulk is compatible with low series resistances. Achieving high efficiencies in SHJ solar cells with TCO-free front contacts requires suppressing deterioration of the passivation quality induced by direct metal-a-Si:H contacts and in-diffusion of metal into the a-Si:H layer. We show that an ozone treatment at the a-Si:H/metal interface suppresses the m...
Phosphorus Catalytic Doping on Intrinsic Silicon Thin Films for the Application in Silicon Heterojunction Solar Cells
ACS Applied Materials & Interfaces
Parasitic absorption and limited fill factor (FF) brought in by the use of amorphous silicon laye... more Parasitic absorption and limited fill factor (FF) brought in by the use of amorphous silicon layers are efficiency-limiting challenges for the silicon heterojunction (SHJ) solar cells. In this work, postdeposition phosphorus (P) catalytic doping (Cat-doping) on intrinsic amorphous silicon (a-Si:H(i)) at a low substrate temperature was carried out and a P concentration of up to 6 × 1021 cm-3 was reached. The influences of filament temperature, substrate temperature, and processing pressure on the P profiles were systemically studied by secondary-ion mass spectrometry. By replacing the a-Si:H(n+er with P Cat-doping of an a-Si:H(i) layer, the passivation quality was improved, reaching an iVOC of 741 mV, while the parasitic absorption was reduced, leading to an increase in JSC by ∼1 mA/cm2. On the other hand, the open-circuit voltage and the FF of a conventional SHJ solar cell (with the a-Si:H(n) layer) can be improved by adding a Cat-doping process on the a-Si:H(i) layer, resulting in an increase in FF by 4.7%abs and in efficiency by 1.5%abs.
Uploads
Papers by Andreas Lambertz