A. N. Tiwari

A. N. Tiwari
Empa - Swiss Federal Laboratories for Materials Science and Technology | Empa · Laboratory for Thin Films and Photovoltaics

PhD

About

396
Publications
93,454
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16,787
Citations
Citations since 2016
129 Research Items
10376 Citations
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201620172018201920202021202205001,0001,500
201620172018201920202021202205001,0001,500
201620172018201920202021202205001,0001,500

Publications

Publications (396)
Article
Full-text available
Bifacial Cu(In,Ga)Se2 (CIGS) solar cells are attractive for a range of applications, but their low power conversion efficiency is a limitation. To improve their efficiency, the formation of GaOx at the CIGS/transparent-conducting-oxide interface and charge recombination near this interface under rear illumination need to be suppressed. In the study...
Preprint
Full-text available
Tin fluoride (SnF2) is an indispensable additive for high-efficiency Pb-Sn perovskite solar cells (PSCs). However, the spatial distribution of SnF2 in the perovskite absorber is seldom investigated while essential for a comprehensive understanding of the exact role of the SnF2 additive. Herein, we revealed the spatial distribution of SnF2 additive...
Article
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Among various types of perovskite‐based tandem solar cells (TSCs), all‐perovskite TSCs are of particular attractiveness for building‐ and vehicle‐integrated photovoltaics, or space energy areas as they can be fabricated on flexible and lightweight substrates with a very high power‐to‐weight ratio. However, the efficiency of flexible all‐perovskite...
Preprint
Full-text available
Among various types of perovskite-based tandem solar cells (TSCs), all-perovskite TSCs are of particular attractiveness for building- and vehicle-integrated photovoltaics, or space energy areas as they can be fabricated on flexible and lightweight substrates with a very high power-to-weight ratio. However, the efficiency of flexible all-perovskite...
Article
Perovskite‐Cu(In,Ga)Se2 (CIGS) thin‐film tandem technology provides an exciting prospect to achieve low‐cost high‐efficiency photovoltaic devices by high throughput roll‐to‐roll processing on flexible substrates. However, no report on flexible perovskite‐CIGS mini‐modules has been published due to scribing related challenges in realizing NIR‐transp...
Article
Carbon-based perovskite solar cells (C-PSCs) are recognized as low-cost stable photovoltaics. However, currently most highly efficient C-PSCs are optically opaque, which means that they can only utilize direct illumination but...
Article
The open-circuit voltage (VOC) is the main limitation to higher efficiencies of Cu(In,Ga)Se2 solar cells. One of the most critical parameters directly affecting VOC is the charge carrier lifetime. Therefore, it is essential to evaluate the extent to which inhomogeneities in material properties limit the carrier lifetime and how postdeposition treat...
Article
Full-text available
The scalability of highly efficient organic-inorganic perovskite solar cells (PSCs) is one of the major challenges of solar module manufacturing. Various scalable methods have been explored to strive for uniform perovskite films of high crystal quality on large-area substrates, but each of these methods has individual limitations on the potential o...
Article
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Two key strategies for enhancing the efficiency of Cu(In,Ga)Se2 solar cells are the bandgap gradient across the absorber and the incorporation of alkali atoms. The combined incorporation of Na and Rb into the absorber has brought large efficiency gains compared to Na-containing or alkali-free layers. Here, transient absorption spectroscopy is emplo...
Preprint
Full-text available
The scalability of highly efficient organic-inorganic perovskite solar cells (PSCs) is one of the remaining challenges of solar module manufacturing. Various scalable methods have been explored to strive for uniform perovskite films of high crystal quality on large-area substrates. However, each of these methods have individual drawbacks, limiting...
Article
Full-text available
Lithium dendrites have become a roadblock in the realization of solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk defects in crystalline electrolytes such as the garnet Li 7 La 3 Zr 2 O 12 (LLZO) facilitates the growth of these hazardous lithium filaments. Here we explore the amorphous phase of LLZO a...
Article
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Electronic transport in a semiconductor is key for the development of more efficient devices. In particular, the electronic transport parameters carrier lifetime and mobility are of paramount importance for the modeling, characterization and development of new designs for solar cells and optoelectronic devices. In this work, we use time-resolved ph...
Article
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Passivation and interlayer engineering are important approaches to increase the efficiency and stability of perovskite solar cells. Thin insulating dielectric films at the interface between the perovskite and the charge carrier transport layers have been suggested to passivate surface defects. Here, we analyze the effect of depositing poly(methyl m...
Article
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The rear interface of kesterite absorbers with Mo back contact represents one of the possible sources of nonradiative voltage losses (ΔVoc,nrad) because of the reported decomposition reactions, an uncontrolled growth of MoSe2, or a nonoptimal electrical contact with high recombination. Several intermediate layers (IL), such as MoO3, TiN, and ZnO, h...
Article
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Protective coatings applied to cathodes help to overcome interface stability issues and extend the cycle life of Li-ion batteries. However, within 3D cathode composites it is difficult to isolate the effect of the coating because of additives and non-ideal interfaces. In this study we investigate niobium oxide (NbO x ) as cathode coating in a thin-...
Article
Full-text available
The performance of Cu(In,Ga)Se2 (CIGS) solar cells is limited by the presence of the highly recombinative CIGS/Mo interface. The recombination at the CIGS/Mo interface is influential for the open circuit voltage (VOC) in high quality CIGS absorbers with increased charge carriers diffusion length. A quantitative understanding of the role of the Ga b...
Article
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The sintering of alumina (Al2O3) traditionally occurs at high temperatures (up to ca. 1700 °C) and in significantly long times (up to several hours), which are required for the consolidation of the material by diffusion processes. Here we investigate the photonic sintering of alumina particles using millisecond flash lamp irradiation with extreme h...
Preprint
Full-text available
Lithium metal dendrites have become a roadblock in the realization of next-generation solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk inhomogeneities with non-negligible electronic conductivity in crystalline electrolytes such as the lithium garnet Li 7 La 3 Zr 2 O 12 (LLZO) facilitates the growth o...
Article
The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recom...
Preprint
Protective coatings applied to cathodes help to overcome interface stability issues and extend the cycle life of Li-ion batteries. However, it is difficult to isolate the effect of the coating because of the additives and non-ideal interfaces within 3D cathode composites. In this study we investigate niobium oxide (NbO<sub>x</sub>) as cathode coati...
Article
Full-text available
Cu(In,Ga)Se2 solar cells have markedly increased their efficiency over the last decades currently reaching a record power conversion efficiency of 23.3%. Key aspects to this efficiency progress are the engineered bandgap gradient profile across the absorber depth, along with controlled incorporation of alkali atoms via post‐deposition treatments. W...
Preprint
Lithium metal dendrites have become a roadblock in the realization of next-generation solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk inhomogeneities with non-negligible electronic conductivity in crystalline electrolytes such as the lithium garnet Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12<...
Article
Thin film deposition of solid electrolytes can be useful for the fabrication of better solid-state batteries by reducing the thickness of the electrolyte material to a few hundred nanometers. This facilitates ionic conductance for faster charge-discharge and reduces the total volume of inactive material, therefore increasing energy and power densit...
Article
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The rapid evolution of the neuromorphic computing stimulates the search for novel brain-inspired electronic devices. Synaptic transistors are three-terminal devices that can mimic the chemical synapses while consuming low power, whereby an insulating dielectric layer physically separates output and input signals from each other. Appropriate choice...
Article
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Metal halide perovskite solar cells (PSCs) have gained tremendous attention due to their high power conversion efficiencies (PCEs) and potential for low‐cost manufacturing. Their wide and tunable bandgap makes perovskites an ideal candidate for tandem solar cells (TSCs) with well‐established narrow bandgap photovoltaic technologies, such as crystal...
Article
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Lithium garnet Li7La3Zr2O12 (LLZO) is being investigated as a potential solid electrolyte for next-generation solid-state batteries, owing to its high ionic conductivity and electrochemical stability against metallic lithium and high potential cathodes. While the LLZO / Li metal anode interface has been thoroughly investigated to achieve almost neg...
Article
Full-text available
The high ionic conductivity and wide electrochemical stability of the lithium garnet Li7La3Zr2O12 (LLZO) make it a viable solid electrolyte for all‐solid‐state lithium batteries with superior capacity and power densities. Contrary to common ceramic processing routes of bulk pellets, thin film solid electrolytes could enable large‐area fabrication,...
Article
Full-text available
Indium tin oxide (ITO) is a transparent conducting material that is widely used in devices where high transparency of the electrodes is required, such as flat panel and liquid crystal displays, touch panels, smart windows, and many others. ITO layers are deposited on a large scale by magnetron sputtering and then structured by lithography to define...
Article
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Four-terminal (4-T) tandem solar cells (e.g., perovskite/CuInSe2 (CIS)) rely on three transparent conduc-tive oxide (TCO) electrodes with high mobility and low free carrier absorption in near-infrared (NIR) re-gion. In this work, a reproducible In2O3:H (IO:H) film deposition process is developed by independently controlling H2 and O2 gas flows duri...
Article
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In the original article, one of the texts was missing in the Acknowledgment section.
Article
High specific power, high stowed packing efficiency, low processing cost, and high tolerance against environmental threats (high energy and charged particle radiation) make perovskite solar cell (PSC) a promising candidate for power generation in space. However, vacuum, as encountered in space, causes perovskite outgassing, raising concern for its...
Article
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Direct nano-scale microanalysis is important for photovoltaic functional thin films to characterize their homogeneity and purity. This demands combining spatial resolution in the micro/nano-scale and sensitivity in the trace-level range, which is at the moment beyond state-of-the-art. As dictated by counting statistics, the reduction of the spot si...
Article
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High efficiency chalcopyrite thin film solar cells generally use chemical bath deposited CdS as buffer layer. The transition to Cd-free buffer layers, ideally by dry deposition methods is required to decrease Cd waste, enable all vacuum processing and circumvent optical parasitic absorption losses. In this study, Zn 1−x Mg x O thin films were depos...
Article
Full-text available
We explore the feasibility of Ag fiber meshes as electron transport layer for high-efficiency flexible Cu(In,Ga)Se2 (CIGS) solar cells. Woven meshes of Ag fibers after UV illumination and millisecond flash-lamp treatment results in a sheet resistance of 17 Ω/sq and a visible transmittance above 85%. Conductive Ag meshes are integrated into flexible...
Article
Full-text available
The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recom...
Article
Full-text available
Garnet Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte due to its wide electrochemical stability window and high Li-ion conductivity. This electrolyte has potential to be employed in the form of thin films for solid-state batteries, a promising approach in the quest for safer batteries with higher energy densities at lower fabrication co...
Article
Full-text available
We reveal an iodine vapor-induced degradation mechanism in formamidinium–lead-iodide-based perovskite solar cells stressed under combined heat and light illumination.
Article
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State‐of‐the‐art Cu(In,Ga)Se2 (CIGS) solar cells are grown with considerably substoichiometric Cu concentrations. The resulting defects, as well as potential improvements through increasing the Cu concentration, have been known in the field for many years. However, so far, cells with high Cu concentrations show decreased photovoltaic parameters. In...
Preprint
Full-text available
We report a proof-of-concept two-terminal perovskite/Cu(In, Ga)Se2 (CIGS) monolithic thin-film tandem solar cell grown on ultra-thin (30-microns thick), light-weight, and flexible polyimide foil with a steady-state power conversion efficiency of 13.2% and a high open-circuit voltage over 1.75 V under standard test condition.
Article
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We report on the use of a high bandgap metal-oxide at the front interface of Cu(In,Ga)Se 2 (CIGS) solar cells in a point contact concept for reduced interface recombination. Highly resistive HfO 2 is applied on the CIGS surface by atomic layer deposition (ALD). Aspects of the surface passivating effect of HfO 2 on CIGS were investigated by time-res...
Article
Recent developments in inkjet printing have shown it to be a viable method for low‐cost and large‐area coating of oxide materials. In article 1800843, S. Bolat et al. report the low‐temperature synthesis of yttrium aluminum oxide (YAlOx) dielectric layers through a combination of inkjet printing of sol–gel precursors and heat‐assisted deep ultravio...
Article
Full-text available
The performance of kesterite (Cu2ZnSn(S,Se)4 ,CZTSSe)) solar cells is hindered by relatively low open circuit voltage (Voc).A reliable quantification of the voltage deficit would be useful to improve kesterite absorbers. The conventional subtraction of qVoc from the absorber band gap is too inaccurate for compositionally complex absorbers like kest...
Article
Full-text available
Flexible, lightweight Cu(In,Ga)Se2 (CIGS) solar cells grown on polymer substrates are a promising technology with fast growing market prospects. However, power conversion efficiencies of solar cells grown at low temperatures (≈450 °C) remain below the efficiencies of cells grown at high temperature on glass substrates. This contribution discusses t...
Article
Full-text available
Time-resolved photoluminescence (TRPL) is applied to determine an effective lifetime of minority charge carriers in semiconductors. Such effective lifetimes include recombination channels in the bulk as well as at the surfaces and interfaces of the device. In the case of Cu(In,Ga)Se2 absorbers used for solar cell applications, trapping of minority...
Article
Full-text available
The knowledge of minority carrier lifetime of a semiconductor is important for the assessment of its quality and design of electronic devices. Time-resolved photoluminescence (TRPL) measurements offer the possibility to extract effective lifetimes in the nanosecond range. However, it is difficult to discriminate between surface and bulk recombinati...