The fullerene C60 is the prevalent electron transport material (ETM) in high-efficiency perovskite/silicon tandem solar cells. However, it introduces intrinsic limitations, including high interfacial non-radiative recombination losses, the formation of mechanically weak interfaces, and high parasitic absorption. Here, we report a non-fullerene ETM based on a meta-carborane core and 9-fluorenylidene malononitrile functional groups (mCB-FMN) that addresses these challenges while maintaining the processing advantages of C60. Thermally evaporated mCB-FMN forms uniform, conformal thin films that enable efficient electron extraction and strongly suppress interfacial non-radiative recombination losses compared to C60. The introduction of this novel ETM further reduces oxygen-induced degradation of the perovskite/ETM interface, improves the nucleation of the SnOx buffer layer grown by atomic layer deposition and enhances interfacial adhesion within the perovskite/ETM/SnOx stack. Its wide optical bandgap is another key advantage, as it minimizes parasitic absorption losses in tandem solar cells. Replacing C60 with mCB-FMN in opaque p-i-n perovskite single-junction devices improves the power conversion efficiency (PCE) by 1.5% (absolute), driven by a 110 meV increase in open-circuit voltage (VOC). Proof-of-concept perovskite/silicon tandem integration of mCB-FMN yields a PCE of 31.3%, surpassing the C60-based reference by 2.4% (absolute) through simultaneous improvements in VOC and short-circuit current density. These results establish mCB-FMN as a novel non-fullerene ETM for perovskite/silicon tandem solar cells that overcomes the performance limitations of conventional C60 and highlight carborane-based compounds as a promising new class of materials for high-efficiency perovskite photovoltaics.

Nickel sulphides have emerged as promising electrocatalysts due to their cost-effectiveness, abundance, and excellent catalytic activity for the hydrogen evolution reaction (HER). Their performance is largely affected by their crystallographic properties, which are intertwined with their electronic structure, electrochemical surface area (ECSA), and catalytic activity. In parallel with a major research interest in nickel sulphide catalysts, there is also the need for a straightforward, simple synthesis approach, such as gas-phase sulphurization, that enables tuning of both crystallographic phases and ECSA. The present study systematically investigates the role of sulphurization process parameters, including the temperature of the sulphurization oven, H2S flow rate, and sulphurization time, in steering phase formation, crystallite growth, and electrochemical surface area, while establishing correlations with HER activity. Utilizing a controlled sulphurization oven with H2S, commercially available nickel electrodes were modified, leading to variations in nickel sulphide phase composition, crystallite size, and thickness. Our findings reveal a simultaneous phase composition and microstructure evolution in response to sulphurization process parameters. The highest HER activity was associated with a combination of Ni3S2 and Ni3S4 phases, which exhibited the highest ECSA among all tested samples, yielding a current density of -210 mAcm-2 at -0.4 V vs RHE. This performance significantly surpasses that of the pristine micropillar-based Ni electrode (-18 mAcm-2) and approaches that of the Pt-coated counterpart (-250 mAcm-2) under the same conditions.

Nickel-based electrodes are widely recognized for their cost-effectiveness and efficiency in the alkaline oxygen evolution reaction (OER), yet further advancements in surface engineering of these electrodes are essential to fully unlock their catalytic potential. This study explores the electrocatalytic performance of several topologies of 3D-structured nickel electrodes decorated by atomic layer deposited (ALD) NiO films for water oxidation. While pristine Ni electrodes already exhibit good performance due to their 3D structure, their native NiO layer is limited by its fixed thickness, chemical composition, and crystallinity. Adopting ALD for surface modification allows to unravel the role of these properties on the OER performance and electrochemical activation. Among the investigated structures in this work, the 3D Ni electrode based on regularly shaped pillars and holes (Ni Veco), stands out as the most promising OER electrocatalyst, both in its pristine state and after ALD NiO modification, surpassing the performance of Ni felt and Ni foam. Moreover, the presence of ALD NiO is demonstrated to significantly alter the surface chemistry and surface energy of Ni electrodes, leading to a notable enhancement of the OER performance. Upon electrochemical activation, thermal and plasma-assisted ALD NiO on Ni Veco demonstrated overpotentials of 470 and 560 mV, respectively, at 500 mA & sdot;cm-2, outperforming pristine Ni Veco (640 mV).

Heterostacks of nickel oxide (NiO) and cobalt oxide (Co3O4) are promising, nonprecious oxygen evolution reaction (OER) catalysts. NiO is particularly notable for its ability to form the active (oxy)hydroxide phase and its ability to scavenge highly active electrolyte-based iron, while Co3O4 is renowned for its high activity and stability. However, the nanoscale design of the investigated structures, typically composites and nanohybrids, hampers their optimization toward efficient OER, as it is challenging to discern contributions from Co3O4, NiO, and their interface. In this respect, atomic layer deposition (ALD) offers the opportunity to systematically investigate the synergy between these materials by enabling subnanometer thickness control of thin-film heterostacks. These heterostacks demonstrate a strong interfacial coupling associated with the epitaxial growth of NiO on polycrystalline Co3O4. Electrochemical analysis in 1 M KOH of stacks with variable NiO thickness, between 0.2 and 13 nm NiO on Co3O4, reveals two distinctive OER activity regimes, with similar to 2 nm NiO as the tipping point. Stacks consisting of less than 2 nm NiO completely transform into an electrolyte-permeable, flaky nickel (oxy)hydroxide film, enhancing the electrochemically active surface area (ECSA) and enabling Co3O4 to contribute to the OER activity. In contrast, stacks consisting of more than a 2 nm-thick NiO overlayer on Co3O4 exhibit incomplete conversion to the (oxy)hydroxide phase, thereby preventing exposure of Co3O4 to the electrolyte. Nevertheless, the underlying Co3O4 promotes enhanced nickel (oxy)hydroxide formation compared to a NiO thin film, resulting in all stacks outperforming NiO. These results underscore the added value of ALD model systems for the design and understanding of ternary oxides' OER electrocatalysts.

The production of green hydrogen heavily depends on the development of cost-effective and efficient electrolyzers for water splitting that are compatible with the intermittent nature of solar and wind energy. Due to the sluggish kinetics of the oxygen evolution reaction (OER), research in the field of earth-abundant OER electrocatalysts is flourishing. In particular, first-row transition metal-based electrocatalysts, such as oxides, phosphates, and sulfides, are promising, and efforts are focused on understanding and enhancing their OER performance by tailoring the electrocatalysts' bulk and surface properties. Atomic layer deposition (ALD) is already an established technology for the deposition of (electro-)catalytically active metal nanoparticles for OER, and it is also gaining traction for the deposition of thin film transition metal-based electrocatalysts. In this review, we showcase how the merits of ALD—such as film conformality, accurate control over film bulk properties (including thickness, chemical composition, and crystallographic phase), and film surface/interface engineering—have accelerated the synthesis of these electrocatalysts and enabled insights into their OER activation mechanisms. While this review focuses on transition metal-based thin films for the OER in mild alkaline environment, it can be anticipated that the highlighted ALD merits will permeate toward other electrocatalytic reactions.

Nickel Sulfides have emerged as promising electrocatalysts for alkaline hydrogen evolution reaction (HER) due to their cost-effectiveness and high catalytic activity. While growing research has focused on the initial catalyst design, less attention has been paid to structural and electrochemical modifications during prolonged HER operation. Understanding these transformations is essential for developing more active and stable nickel sulphide-based HER catalysts. This study investigated the post-HER evolution of various nickel sulphide crystalline catalysts, including NiS, NiS2, Ni3S2, and Ni3S4, after prolonged cyclic voltammetry (CV) cycling and constant current polarization. Upon 500 CV sweeps, Raman spectroscopy confirmed structural phase transformation of all nickel Sulfides toward Ni3S2, i.e., the most HER-active phase, irrespective of their initial chemical composition. This electrochemical activation process led to an improvement in electrochemical surface area and charge-transfer properties. Moreover, the kinetic analysis indicated a shift in the rate-determining step from a Volmer-limited mechanism to a mixed Volmer-Heyrovsky pathway, contributing to enhanced HER kinetics. Sulfur leaching was identified as a key factor in this transformation, facilitating surface restructuring and exposure of active Ni sites to the electrolyte. Importantly, post-stability characterization confirmed that leaching occurs predominantly during initial activation and ceases thereafter, with no further structural changes over prolonged operation.

Nickel oxide (NiO) is a promising p-type semiconductor extensively investigated for applications in photovoltaics, electrochemical energy storage, and gas sensors. Several deposition techniques, including solution processing, sputtering, chemical vapor deposition, and atomic layer deposition (ALD), are adopted for the synthesis of NiO films. Among these techniques, ALD is recognized for the merit of delivering pinhole-free and conformal films, relevant for processing on textured surfaces. In the present study, we have adopted three ALD NiO processes to deliver films differing in stoichiometry, crystallographic, and optoelectrical properties. To this purpose, the Ni(Bu-t-MeAMD)(2)-based thermal ALD process ("NiOBu-MeAMD"), the Ni(MeCp)(2)-based plasma-assisted ALD (PA-ALD) process ("NiOMeCp"), and the newly developed PA-ALD process, based on the novel Alanis (TM) precursor ("NiOAlanis"), are compared. The NiOAlanis-based process exhibits a linear growth on c-Si/ native oxide with a growth per cycle (GPC) of 0.27 +/- 0.02 & Aring;/cycle at 150 degrees C, similar to the NiOMeCp process, whereas the NiOBu-MeAMD process is characterized by a higher GPC of 0.43 +/- 0.01 & Aring;/cycle. The NiOAlanis films have the lowest Ni-to-O ratio (0.82 +/- 0.04) compared to NiOMeCp (0.96 +/- 0.05) and NiOBu-MeAMD (0.93 +/- 0.05). The excess oxygen in the NiOAlanis films points to a larger relative content of Ni3+ acceptor states. The presence of Ni3+ states contributes to sub-bandgap absorption, leading to a lower transmittance of the NiOAlanis films (similar to 79%) as compared to the NiOMeCp (similar to 84%) and NiOBu-MeAMD films (similar to 90%) in the visible range. In parallel, the resistivity of the (similar to 9 nm) NiOAlanis films (6 +/- 2 Omega cm) is lower than NiOMeCp (66 +/- 33 Omega cm) and NiOBu-MeAMD films [(1.7 +/- 0.1) x 10(4) Omega cm], supporting the observation of the presence of a larger Ni3+ content. Transmission electron microscopy images reveal the presence of a relatively higher density of grain boundaries in NiOBu-MeAMD films that can affect carrier mobility. Furthermore, the PA-ALD NiO films exhibit a higher density (6.9 +/- 0.8 g/cm(3)) than the thermal ALD NiOBu-MeAMD films (5.1 +/- 0.5 g/cm(3)) due to the ion flux impinging on the surface during the O-2 plasma half-cycle. Our study demonstrates that the ALD process influences the stoichiometry and microstructure of the NiO film, ultimately impacting its electrical and optical properties. Additionally, we reflect on the selection of ALD processes for specific application areas. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

The development of a sustainable energy system relies on the production of green hydrogen. One of the major challenges for water splitting is the synthesis of platinum group metal-free oxygen evolution reaction (OER) electrocatalysts. Spinel nickel cobalt oxides (NCOs) have attracted particular interest due to their stable electrocatalytic performance. The less researched rock-salt NCOs, however, are also promising due to their ability to convert to the OER-active hydroxide phase1. Further development of NCO electrocatalysts requires fundamental understanding of their crystallographic structure-OER performance relationship. This work addresses ~20 nm atomic layer deposited (ALD) NCO thin film systems with a broad composition range to unravel the above-mentioned relationship. Our previously developed ALD supercycle process2 based on Ni(MeCp)2, CoCp2 and O2 plasma is employed to generate a full range of chemical compositions, such that the phase transition from Ni-rich rock-salt films to Co-rich films at ~55 at.% Co can be observed. Extensive material characterisation reveals that the phase transition is accompanied by an increase in the +3/+2 ratio of the oxidation state of both Ni and Co. Electrochemical analysis in 1M KOH shows an optimal performance for the 30 at.% Co rock-salt film after 500 CV cycles and a synergistic effect between cobalt and nickel such that NCO films are more OER active than Co3O4 and NiO. The films show a composition-dependent activation during CV cycling, where a decrease in activation is observed for increasing Co at.%. No activation is observed for the spinel films. The activation is driven by bulk transformation to the active (oxy)hydroxide phase and is accompanied by an increase in electrochemical surface area (ECSA) up to a factor 8 for rock-salt films. The overpotential after cycling is corrected for the increase in ECSA using an original method, which reveals that Ni-rich spinel structure films are intrinsically more active3. The use of model systems in combination with extensive material characterisation and prolonged electrochemical testing allows us to distinguish two classes of NCO catalysts, the instantly active and highly stable Co-rich spinel films and the high surface area Ni-rich rock-salt phase which develops upon extensive activation . Placing these results in perspective, we conclude that application of these catalysts on high surface area 3D electrodes would benefit from the more intrinsically active spinel NCO films, whilst activated rock-salt films would be the preferred choice for thin film electrocatalysis studies. These results also show that rock-salt NCO films (<40 at.% Co) could be a more sustainable alternative to the more commonly used spinel NCO films. 1Gebreslase et al. J. Energy Chem. 2022, 67, 101-137 2van Limpt et al. JVSTA, 2023, 41, 032407 3van Limpt et al. Adv. Energy Mat. under review Figure 1

Nickel cobalt oxides (NCOs) are promising, non-precious oxygen evolution reaction (OER) electrocatalysts. However, the stoichiometry-dependent electrochemical behavior makes it crucial to understand the structure-OER relationship. In this work, NCO thin film model systems are prepared using atomic layer deposition. In-depth film characterization shows the phase transition from Ni-rich rock-salt films to Co-rich spinel films. Electrochemical analysis in 1 m KOH reveals a synergistic effect between Co and Ni with optimal performance for the 30 at.% Co film after 500 CV cycles. Electrochemical activation correlates with film composition, specifically increasing activation is observed for more Ni-rich films as its bulk transitions to the active (oxy)hydroxide phase. In parallel to this transition, the electrochemical surface area (ECSA) increases up to a factor 8. Using an original approach, the changes in ECSA are decoupled from intrinsic OER activity, leading to the conclusion that 70 at.% Co spinel phase NCO films are intrinsically the most active. The studies point to a chemical composition dependent OER mechanism: Co-rich spinel films show instantly high activities, while the more sustainable Ni-rich rock-salt films require extended activation to increase the ECSA and OER performance. The results highlight the added value of working with model systems to disclose structure-performance mechanisms.

Locally controlling the position of electrodes in 3D can open new avenues to collect electrochemical signals in complex sensing environments. Implementing such electrodes via an electrical network requires advanced fabrication approaches. This work uses corner lithography and Pt ALD to produce electrochemical 3D electrodes. The approach allows the fabrication of (sub)micrometer size Pt octahedra electrodes spatially supported over 3D fractal-like structures. As a proof of concept, electrochemical sensing of ferrocyanide in biofouling environments, e.g., bovine serum albumin (BSA) and Pseudomonas aeruginosa (P. aeruginosa), is assessed. Differences between before and after BSA addition show a reduction in the active electrode surface area (Delta Aeff) approximate to 49% +/- 7% for the flat electrode. In comparison, a Delta Aeff reduction of 25% +/- 2% for the 3D electrode has been found. The results are accompanied by a 24% +/- 16% decrease in peak current for the flat Pt substrate and a 14% +/- 5% decrease in peak current for the 3D electrode 24 h after adding BSA. In the case of P. aeruginosa, the 3D electrode retains electrochemical signals, while the flat electrode does not. The results demonstrate that the 3D Pt electrodes are more stable than their flat counterparts under biofouling conditions. A fabrication method for the spatial patterning of Pt octahedra is introduced. Electrochemical sensing is carried out to demonstrate the electrochemical readout capabilities of the Pt octahedra under biofouling conditions. In the near future, the technology can habilitate local electrochemical sensing over a Pt octahedron in more complex cellular environments.image

Two terminal (2T) perovskite /copper-indium-gallium-selenide (CIGS) tandem solar cells combine high conversion efficiency with lightweight flexible substrates which can decrease manufacturing and installation costs. In order to improve the power conversion efficiency of these tandem solar cells, the use of advanced simulation tools is crucial to estimate the loss mechanisms. In this regard, most of the available simulation works on tandem solar cells are oriented to minimize optical losses and assuming simplifications for the electrical simulations in particular in the top and bottom cell interconnection at the so-called tunnel recombination junction (TRJ) neglecting the inner physics of the complete tandem device. Therefore, the effect of charge exchange mechanism between top and bottom soler cells on the external parameters of a tandem devices is not fully understood yet. In this work, we present an experimentally validated opto-electrical model based on the fundamental semiconductor equations for the study of loss mechanisms of a reference perovskite/CIGS solar cell. Different from other numerical works, because our simulation platform includes the fundamental working mechanisms of the layers comprising the TRJ, we can properly calculate the losses related to it. We firstly present the calibration and validation of our opto-electrical model with respect to three fabricated reference solar cells: top cell only, bottom cell only and tandem device. Then, we use the calibrated model to evaluate main loss mechanisms affecting the baseline tandem device. Finally, we use the model to propose a roadmap for the optimization of monolithic perovskite/CIGS tandem solar cells.

Atomic layer deposition (ALD) of Li-containing thin films is deemed as highly relevant for the development of next-generation Li-ion batteries. Lithium hexamethyldisilazide (LiHMDS), as Li-containing precursor, is preferred over the widely used lithium tert-butoxide because of its lower melting point of 70 °C. However, the presence of silyl groups in the LiHMDS chemical structure can result in the undesired incorporation of Si in the film. Therefore, understanding the reaction mechanism of LiHMDS is required to control its dual-source behavior and grow Si-free Li-containing thin films. For this purpose LiHMDS was combined with O2 plasma or water as coreactant. In situ spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) revealed that using O2 plasma as coreactant results in linear growth and Si-containing films, whereas using H2O as coreactant leads to fast, nonsurface-reaction-limited growth and Si-free films. To shed light on the role of the coreactant on the reaction mechanism of LiHMDS, in situ studies by time-resolved quadrupole mass spectrometry (QMS) were performed on the O2 plasma and H2O-based ALD processes. Measurements taken during full ALD cycles and half-cycles were carefully compared to identify which half-cycle surface reaction products lead to silicon incorporation in the film. The QMS results of the LiHMDS + H2O process showed that LiHMDS both chemisorbs and physisorbs. Furthermore, it is concluded that Si incorporation occurs during the O2 plasma step, when the physisorbed ligands are combusted and Si-containing products are redeposited. This work also demonstrates that the incorporated Si can be abstracted from the film by means of a H2 plasma step following the O2 plasma step. These insights on the role of the coreactant in the synthesis of Li-containing films contribute to the development of LiHMDS-based ALD processes for Li-ion battery applications.

Recent reports have shown that nickel oxide (NiO) when adopted as a hole transport layer (HTL) in combination with organic layers, such as PTAA or self-assembled monolayers (SAMs), leads to a higher device yield for both single junction as well as tandem devices. Nevertheless, implementing NiO in devices without PTAA or SAM is seldom reported to lead to high-performance devices. In this work, we assess the effect of key NiO properties deemed relevant in literature, namely- resistivity and surface energy, on the device performance and systematically compare the NiO-based devices with those based on PTAA. To this purpose, (thermal) atomic layer deposited (ALD) NiO (NiOBu-MeAMD), Al-doped NiO (Al:NiOBu-MeAMD), and plasma-assisted ALD NiO (NiOMeCp) films, characterized by a wide range of resistivity, are investigated. Although Al:NiOBu-MeAMD (similar to 400 Omega cm) and NiOMeCp(similar to 80 Omega cm) films have a lower resistivity than NiOBu-MeAMD (similar to 10 k Omega cm), the Al:NiOBu-MeAMD and NiOMeCp-based devices are found to have a modest open circuit voltage (V-OC) gain of similar to 30 mV compared to NiOBu-MeAMD-based devices. Overall, the best-performing NiO-based devices (similar to 14.8% power conversion efficiency (PCE)) still lag behind the PTAA-based devices (similar to 17.5%), primarily due to a V-OC loss of similar to 100 mV. Further investigation based on light intensity analysis of the V-OC and FF and the decrease in V-OC compared to the quasi-Fermi level splitting (QFLS) indicates that the V-OC is limited by trap-assisted recombination at the NiO/perovskite interface. Additionally, SCAPS simulations show that the presence of a high interfacial trap density leads to a V-OC loss in NiO-based devices. Upon passivation of the NiO/perovskite interface with Me-4PACz, the V-OC increases by 170-200 mV and is similar for NiOBu-MeAMD and Al:NiOBu-MeAMD, leading to the conclusion that there is no influence of the NiO resistivity on the V-OC once interface passivation is realized. Finally, our work highlights the necessity of comparing NiO-based devices with state-of-the-art HTL-based devices to draw conclusion about the influence of specific material properties on device performance.

On the VOC Loss in NiO-based Inverted Metal Halide Perovskite Solar CellsKousumi Mukherjee a, Denise Kreugel a, Nga Phung a, Cristian van Helvoirt a, Valerio Zardetto b, Mariadriana Creatore a, ca Department of Applied Physics, Eindhoven University of Technology, partner in Solliance, P.O. Box 513, 5600 MB Eindhoven, The Netherlandsb TNO, partner in Solliance, High Tech Campus 21, 5656 AE Eindhoven, The Netherlandsc Eindhoven Institute of Renewable Energy Systems (EIRES), PO Box 513, 5600 MB Eindhoven, The NetherlandsInternational Conference on Hybrid and Organic PhotovoltaicsProceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV24)València, Spain, 2024 May 12th - 15thOrganizer: Bruno EhrlerOral, Kousumi Mukherjee, presentation 054DOI: https://doi.org/10.29363/nanoge.hopv.2024.054Publication date: 6th February 2024A perovskite p-i-n architecture PV device generally adopts solution-processed organic hole transport layers (HTLs), like PTAA or self-assembled monolayers (SAMs). However, this approach can result in an inhomogeneous HTL surface coverage, especially when processed on textured substrates [1-2]. Recent reports have shown that the adoption of atomic layer deposited (ALD) nickel oxide (NiO) in combination with organic layers, such as PTAA or SAM, addresses the above-mentioned issue and leads to higher device yield, for both single junction [3] as well as tandem (in combination with c-Si or CIGS) devices [1-2]. Nevertheless, implementing NiO in devices without PTAA or SAM is seldom reported to lead to highly performing devices. In the present contribution, we systematically assess the effect of key properties of NiO deemed relevant in literature, namely- resistivity and surface energy, on the device performance and compare the ALD NiO-based devices to those based on PTAA. To this purpose, (thermal) atomic layer deposited (ALD) NiO, Al-doped NiO, and plasma-assisted ALD (PA-ALD) NiO films are investigated as HTLs in a single junction mid-bandgap perovskite solar cell. The resistivity of Al-doped NiO and PA-ALD NiO films are 400 Ω∙cm and 80 Ω∙cm respectively and they are lower than that of thermal ALD NiO (10 kΩ∙cm). However, the devices implementing Al-doped and PA-ALD NiO HTLs exhibit only a modest VOC gain of ~30 mV compared to thermal ALD NiO-based devices. Overall, the best-performing NiO-based devices (~14.8% PCE) still lag behind the PTAA-based devices (~17.5%) primarily due to a VOC loss of ~100 mV. Moreover, we observe that the average grain size and the overall crystal quality of the perovskite absorber, which can impact the VOC, is not affected by the surface energy of the different NiO HTLs. Further investigation based on the light intensity analysis of the VOC and FF and the decrease in VOC compared to the quasi-Fermi level splitting (QFLS), indicate that the VOC is limited by trap-assisted recombination at the NiO/ perovskite interface and that a better charge extraction occurs when PTAA is adopted. Additionally, SCAPS simulations show that the VOC of the NiO-based devices decreases when trap states are present at the NiO/ perovskite interface. Whilst tuning the resistivity of NiO has a negligible impact on the device performance, we also show that passivating the NiO/ perovskite interface with Me-4PACz SAM recovers this VOC loss with an increase of ~200 mV. Our study shows that the potential positive effect of decreasing NiO bulk resistivity on the device performance is shadowed by the high recombination at the NiO/perovskite interface. Lastly, our work highlights the necessity of comparing devices based on emerging transport layers, such as NiO, with state-of-the-art transport layers-based devices, which is often neglected in the literature, in order to draw conclusion about the influence of specific material properties on the device performance. References:[1] Phung, N.; Zhang, D.; van Helvoirt, C.; Verhage, M.; Verheijen, M.; Zardetto, V.; Bens, F.; Weijtens, C. H. L.; Geerligs, L. J. (Bart); Kessels, W. M. M.; Macco, B.; Creatore, M. Atomic Layer Deposition of NiO Applied in a Monolithic Perovskite/PERC Tandem Cell. Solar Energy Materials and Solar Cells 2023, 261, 112498[2] Jošt, M.; Bertram, T.; Koushik, D.; Marquez, J. A.; Verheijen, M. A.; Heinemann, M. D.; Köhnen, E.; Al-Ashouri, A.; Braunger, S.; Lang, F.; Rech, B.; Unold, T.; Creatore, M.; Lauermann, I.; Kaufmann, C. A.; Schlatmann, R.; Albrecht, S. 21.6%-Efficient Monolithic Perovskite/Cu(In,Ga)Se 2 Tandem Solar Cells with Thin Conformal Hole Transport Layers for Integration on Rough Bottom Cell Surfaces. ACS Energy Lett. 2019, 4 (2), 583–590.[3] Phung, N.; Verheijen, M.; Todinova, A.; Datta, K.; Verhage, M.; Al-Ashouri, A.; Köbler, H.; Li, X.; Abate, A.; Albrecht, S.; Creatore, M. Enhanced Self-Assembled Monolayer Surface Coverage by ALD NiO in p-i-n Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2022, 14 (1), 2166–2176.Acknowledgements:This work is carried out under the "New Energy and Mobility Outlook for the Netherlands" (NEON) project with project number 17628 of the research programme NWO Crossover which is (partly) financed by the Dutch Research Council (NWO). The authors would like to thank Dr. Christ H.L. Weijtens for carrying out the UPS measurements, Wim Arnold Bik (from Detect 99) for carrying out the RBS measurement and Caspar O. van Bommel, Joris J. I. M. Meulendijks, and Janneke J. A. Zeebregts for their technical support. K.M. acknowledges Wouter Vereijssen for his contribution in the surface energy studies. K.M. thanks Dr. Sinclair Ryley Ratnasingham for his insightful comments and help in the SCAPS simulation. M.C. acknowledges the NWO Aspasia program. 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Anion exchange membrane water electrolysis (AEMWE) is a promising technology for renewable electricity-driven water splitting toward hydrogen production. However, application of AEMWE at industrial scale requires the development of oxygen evolution reaction (OER) electrocatalysts showing long-term stability under mild alkaline conditions. Among these, nickel cobalt oxide thin films are considered promising candidates. The ideal chemical composition of these oxides remains debatable, with recent literature indicating that rock-salt NiCoO2 may exhibit similar OER activity as the traditional spinel NiCo2O4. In this work, we present the development of a plasma-enhanced atomic layer deposition (ALD) process of nickel cobalt oxide thin films (∼20 nm) with focus on the role of their chemical composition and crystal structure on the OER activity. The film composition is tuned using a supercycle approach built upon CoOx cycles with CoCp2 as a precursor and O2 plasma as a co-reactant and NiOx cycles with Ni(MeCp)2 as a precursor and O2 plasma as a co-reactant. The films exhibit a change in the crystallographic phase from the rock-salt to spinel structure for increasing cobalt at. %. This change is accompanied by an increase in the Ni3+-to-Ni2+ ratio. Interestingly, an increase in electrical conductivity is observed for mixed oxides, with an optimum of (2.4 ± 0.2) × 102 S/cm at 64 at. % Co, outperforming both NiO and Co3O4 by several orders of magnitude. An optimal electrocatalytic performance is observed for 80 at. % Co films. Cyclic voltammetry measurements simultaneously show a strong dependence of the OER-catalytic performance on the electrical conductivity. The present study highlights the merit of ALD in controlling the nickel cobalt oxide chemical composition and crystal structure to gain insight into its electrocatalytic performance. Moreover, these results suggest that it is important to disentangle conductivity effects from the electrocatalytic activity in future work.

NiO-based electrocatalysts, known for their high activity, stability, and low cost in alkaline media, are recognized as promising candidates for the oxygen evolution reaction (OER). In parallel, atomic layer deposition (ALD) is actively researched for its ability to provide precise control over the synthesis of ultrathin electrocatalytic films, including film thickness, conformality, and chemical composition. This study examines how NiO bulk and surface properties affect the electrocatalytic performance for the OER while focusing on the prolonged electrochemical activation process. Two ALD methods, namely, plasma-assisted and thermal ALD, are employed as tools to deposit NiO films. Cyclic voltammetry analysis of ∼10 nm films in 1.0 M KOH solution reveals a multistep electrochemical activation process accompanied by phase transformation and delamination of activated nanostructures. The plasma-assisted ALD NiO film exhibits three times higher current density at 1.8 V vs RHE than its thermal ALD counterpart due to enhanced β-NiOOH formation during activation, thereby improving the OER activity. Additionally, the rougher surface formed during activation enhanced the overall catalytic activity of the films. The goal is to unravel the relationship between material properties and the performance of the resulting OER, specifically focusing on how the design of the material by ALD can lead to the enhancement of its electrocatalytic performance.

The metal halide perovskite absorbers are prone to surface defects, which severely limit the power conversion efficiencies (PCEs) and the operational stability of the perovskite solar cells (PSCs). Herein, trace amounts of bithiophene propylammonium iodide (bi-TPAI) are applied to modulate the surface properties of the gas-quenched perovskite. It is found that the bi-TPAI surface treatment has negligible impact on the perovskite morphology, but it can induce a defect passivation effect and facilitate the charge carrier extraction, contributing to the gain in the open-circuit voltage (V oc) and fill factor. As a result, the PCE of the gas-quenched sputtered NiO x -based inverted PSCs is enhanced from the initial 20.0% to 22.0%. Most importantly, the bi-TPAI treatment can largely alleviate or even eliminate the burn-in process during the maximum power point tracking measurement, improving the operational stability of the devices.

Perovskite photovoltaics has achieved conversion efficiencies of 26.0% by optimizing the optoelectronic properties of the absorber and its interfaces with charge transport layers (CTLs). However, commonly adopted organic CTLs can lead to parasitic absorption and device instability. Therefore, metal oxides like atomic layer-deposited (ALD) SnO2 in combination with fullerene-based electron transport layers have been introduced to enhance mechanical and thermal stability. Instead, when ALD SnO2 is directly processed on the absorber, i.e., without the fullerene layer, chemical modifications of the inorganic fraction of the perovskite occur, compromising the device performance. This study focuses on the organic fraction, particularly the formamidinium cation (FA+), in a CsFAPb(I,Br)3 perovskite. By employing in situ infrared spectroscopy, we investigate the impact of ALD processing on the perovskite, such as vacuum level, temperature, and exposure to half and full ALD cycles using tetrakis(dimethylamido)-Sn(IV) (TDMA-Sn) and H2O. We observe that exposing the absorber to vacuum conditions or water half-cycles has a negligible effect on the chemistry of the perovskite. However, prolonged exposure at 100 °C for 90 min results in a loss of 0.7% of the total formamidinium-related vibrational features compared to the pristine perovskite. Supported by density functional theory calculations, we speculate that FA+ deprotonates and that formamidine desorbs from the perovskite surface. Furthermore, the interaction between TDMA-Sn and FA+ induces more decomposition of the perovskite surface compared to vacuum, temperature, or H2O exposure. During the exposure to 10 ALD half-cycles of TDMA-Sn, 4% of the total FA+-related infrared features are lost compared to the pristine perovskite. Additionally, IR spectroscopy suggests the formation and trapping of sym-triazine, i.e., a decomposition product of FA+. These studies enable to decouple the effects occurring during direct ALD processing on the perovskite and highlight the crucial role of the Sn precursor in affecting the perovskite surface chemistry and compromising the device performance.

Monolithic perovskite/c-Si tandem solar cells have attracted enormous research attention and have achieved efficiencies above 30%. This work describes the development of monolithic tandem solar cells based on silicon heterojunction (SHJ) bottom-and perovskite top-cells and highlights light management techniques assisted by optical simulation. We first engineered (i)a-Si:H passivating layers for (100)-oriented flat c-Si surfaces and combined them with various (n)a-Si:H, (n)nc-Si:H, and (n)nc-SiOx:H interfacial layers for SHJ bottom-cells. In a symmetrical configuration, a long minority carrier lifetime of 16.9 ms was achieved when combining (i)a-Si:H bilayers with (n)nc-Si:H (extracted at the minority carrier density of 1015 cm-3). The perovskite sub-cell uses a photostable mixed-halide composition and surface passivation strategies to minimize energetic losses at charge-transport interfaces. This allows tandem efficiencies above 23% (a maximum of 24.6%) to be achieved using all three types of (n)-layers. Observations from experimentally prepared devices and optical simulations indicate that both (n)nc-SiOx:H and (n)nc-Si:H are promising for use in high-efficiency tandem solar cells. This is possible due to minimized reflection at the interfaces between the perovskite and SHJ sub-cells by optimized interference effects, demonstrating the applicability of such light management techniques to various tandem structures.