Interdigitated-back-contacted silicon heterojunction (IBC-SHJ) solar cells with molybdenum oxide (MoOx) as a hole transport layer and a novel (n)-type hydrogenated nanocrystalline silicon (nc-Si:H)/MoOx electron transport stack use ultra-thin MoOx as a full-area blanket layer. This solar cell architecture is realized with a simplified fabrication process and ensures high shunt resistances, attributed to the low lateral conductivity of the MoOx layer. Here we investigate the electron transport mechanisms through the electron collection contact to improve the understanding and performance of the IBC-SHJ solar cells. For this evaluation, we first introduce plasma treatments between (n)nc-Si:H and MoOx and assess their role in passivation, charge carrier transport and MoOx growth. Temperature-dependent current-voltage (I-V) measurements of front/back-contacted (FBC) solar cells with (n)nc-Si:H/MoOx stack, supported by high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDX) imaging and numerical simulations, reveal that plasma treatment (PT) and plasma treatment with boron (PTB) enable electron transport based on direct energy transitions. Next, we perform thickness sensitivity analysis to find the optimal layer thicknesses of (n)nc-Si:H and MoOx. While FBC-SHJ devices exhibit stable performance across a broad range of (n)nc-Si:H thicknesses (10-50 nm), IBC-SHJ devices are more sensitive to such a thickness variation, with thinner (n)-layers limiting final device efficiency. The combination of 50-nm thick (n)nc-Si:H, PTB, and 1.7-nm thick MoOx enables the best performance of IBC-SHJ solar cells. When metallized with electroplated Cu, our champion IBC-SHJ solar cell with MoOx blanket layer reaches an efficiency of 23.59%. Further advancements in (n)nc-Si:H properties, passivation, transparent conductive oxide selection, and front-side light management are expected to drive efficiencies well above 24%.

Hybrid organic-inorganic perovskites (PVKs) offer exceptional optoelectronic performance, yet reproducible and scalable co-evaporation remains challenging. This study examines the interplay of factors affecting compositional control during three-source PVK deposition. We identify chamber pressure, precursor cross-contamination, and flux instability - especially from organic salts such as formamidinium iodide (FAI) - as major sources of variability. A critical influence is the occurrence of cross-reading, where omnidirectional evaporation of FAI contributes to the reading on the quartz crystal microbalance (QCM) sensors monitoring the inorganic precursors like caesium bromide (CsBr) and lead iodide (PbI2) even though shielding is present. This effect, strongly dependent on FAI load, deposition rate, and QCM sensor position, erroneously inflates measured fluxes, leading to inaccurate rate control and unintentional compositional drift. Maintaining A-, B- and X-site stoichiometry therefore requires dynamic adjustment of precursor rates, particularly at higher deposition speeds where mean free path limitations come into play. We demonstrate the successful deposition of perovskite layers at a deposition speed of 27.8 nm min-1 as the practical ceiling for the investigated CsxFA1-xPb(I1-xBrx)3 composition within our experimental framework. These findings highlight the delicate balance between deposition speed, precursor stability, and film quality, underscoring the need for improved delivery systems - such as continuous precursor feedthrough, multiple organic sources, alternative vapor transport or flash evaporation methods - to achieve reproducible, fast and large-scale fabrication of high-performance PVK films.

Partial shading remains a critical challenge for perovskite photovoltaics, as shaded cells in otherwise illuminated modules operate in reverse bias, which can accelerate degradation. In other solar cell technologies, reverse bias electroluminescence (ReBEL) imaging has been successfully employed to investigate the reverse bias breakdown mechanism. Here, ReBEL imaging is proposed as technique for imaging the local reverse bias current flow on perovskite solar cells. To that end, the ReBEL signal is affirmed to originate from radiative recombination in the absorber layer. ReBEL imaging is compared to established thermal current imaging techniques and reveals superior sensitivity and spatial resolution while showing similar features in the investigated samples. Further experiments reveal a dependence on the reverse bias current: The spatial distribution of the ReBEL signal differs significantly between small and large current injection levels. This could point towards two different breakdown mechanisms. These results show that, despite some open questions, ReBEL imaging could help understand the reverse bias behavior of perovskite solar cells better.

The degradation of perovskite solar cells due to reverse bias (RB) is one of the remaining challenges hindering the commercialization of the technology. To overcome this challenge, a thorough understanding of and control over the breakdown (BD) voltage are crucial. A prerequisite for this is that the community "speaks the same language," that is, that the reported BD voltages are comparable. A review of literature data shows that the impact of measurement parameters is often unknown and seems to depend strongly on sample properties. It follows that standardization is the only way to reach comparability. Here, a set of measurement parameters to fill this gap is proposed. Additionally, various definitions of a "BD voltage" are used in parallel without any way of relating them to each other; this metric and its determination need to be considered as well. After a thorough discussion of the available definitions, the use of the point of maximum curvature is introduced. Its main advantage is the possible connection to an analytical description of the BD mechanism. In this way, a starting point for scientists new to the field of RB stability is provided, and the ground for a broader discussion in the community is prepared.

Low bandgap (LBG) Pb–Sn perovskites (PVKs) are key absorber materials for high-efficiency all-perovskite tandem solar cells. Yet, their fabrication at device-relevant thicknesses with high structural and optoelectronic quality remains challenging. Here, we demonstrate the scalable deposition of formamidinium lead tin triiodide (FAPb0.5Sn0.5I3) films up to 700 nm thick using a single cycle of sequential thermal evaporation (1c-sTE). The process relies on vacuum deposition of a PbSnI4 alloy followed by FAI, without the need for additives typically used in solution processing. Optical spectroscopy, XRD, solid-state NMR, and TRMC measurements reveal that FAI readily diffuses into the inorganic precursor layer even at room temperature. Independent of the precursor mixing time, annealing is required to achieve films with increased local homogeneity, large grains, and high crystallinity, leading to reduced defect density, increased carrier mobility up to 80 cm2 (Vs−1), and lifetimes close to a microsecond. The resulting films are stoichiometrically uniform across their thickness and exhibit dense, columnar grain morphologies. A device with the architecture ITO/PEDOT:PSS/FAPb0.5Sn0.5I3/C60/BCP/Ag, shows power conversion efficiencies of 10%, with voltage losses mainly at the PEDOT:PSS/PVK interface. This work demonstrates that 1c-sTE is a feasible method for producing LBG Pb–Sn PVK films suitable for PV applications.

Tuning the nanoroughness of ( n )nc-Si:H in bottom cells controls SAM anchoring and work function shifts in monolithic perovskite–silicon tandems. Enhanced nanoroughness improves interface quality and fill factor, enabling efficiencies up to 32.6%.

The integration of self-assembled monolayers (SAMs) in perovskite (PVK) solar cells often presents processing challenges that can hinder their industrial uptake. To address these limitations and enhance the manufacturability of the SAMs/PVK interface, a co-deposition strategy was recently developed, wherein both SAMs and PVK films are formed simultaneously in a single step. As the fundamental principles governing the SAM/PVK co-deposition process remain insufficiently explored, here we selected four commercially available SAMs molecules─MeO-4PACz, Me-4PACz, Me-2PACz, and 2PACz─and we mixed them based on their molecular size, polarity, and hydrophobicity, forming pairs. The co-deposition process of mixed-SAMs with MAPbI3 precursor solutions was studied, and corresponding solar cell devices were fabricated. Among the three combinations tested, the MeO-4PACz + Me-4PACz one yields the most promising results, and a power conversion efficiency of approximately 19% was achieved without any additional passivation strategies. Our findings reveal that the co-deposition process of mixed-SAMs is primarily influenced by the interplay between molecular size and polarity. The binding strength of co-deposited mixed SAMs to the In2O3:Sn (ITO) substrate is largely dictated by their solvation behavior in the PVK precursor-DMF:DMSO solvent system. This conclusion is supported by quantum chemistry calculations and further corroborated by surface, structural, and compositional analysis.

Throughout the development of silicon heterojunction (SHJ) solar cells, the transparent conductive oxide has been regarded as an essential component of their front electrode, facilitating lateral charge transport of photogenerated carriers toward the front metal grid fingers. In rear junction (RJ)‐SHJ solar cells, the ( n )c‐Si bulk is known to support the lateral electron transport at maximum power point injection level, provided that the contact resistance of the front contact stack is sufficiently low. This enables experimental RJ‐SHJ solar cell architectures featuring a localized front carrier‐selective passivating contact exclusively covering the area contacted by the metal grid. Herein, a top‐down approach to the synthesis of this type of architecture is studied and its optical and electrical performance applied to different ( n )‐type contacts are investigated. Additionally, the potential of the localized contact architecture through Cu‐plated RJ‐SHJ solar cells is demonstrated. These solar cell demonstrators feature high short‐circuit current density of 40.5 mA cm −2 , without significantly compromising their open‐circuit voltage or fill factor, enabling efficiencies well above 23%, a 2% abs improvement compared to their state before localization of the front contact.

Polycrystalline silicon (poly-Si) carrier-selective passivating contacts (CSPCs), featuring high photoconversion efficiency (PCE) and cost-effectiveness, have emerged as a promising approach for high-efficiency crystalline silicon (c-Si) solar cells. To minimize parasitic absorption losses induced by doped poly-Si window layers, wide bandgap oxygen-alloyed poly-Si (poly-SiOx) layers are developed. However, challenges persist in achieving excellent surface passivation for boron-doped poly-SiOx contact stacks, likely caused by boron diffusion during annealing and the reduced doping concentration resulting from lower crystallinity as oxygen content increases. In this study, we investigate the impact on the passivating contact structure and solar cell performance of a 10nm thick intrinsic hydrogenated amorphous silicon buffer layer with varying oxygen content (a-Si (Ox):H) deposited by plasma-enhanced chemical vapor deposition (PECVD), and placed between the tunneling silicon oxide (SiOx) and the poly-SiOx (p+). After the hydrogenation step, we obtain both high passivation quality with implied open circuit voltage (iVoc) of 728.3 mV and low contact resistivity (rho c) of 59.18 m Omega cm2 on polished surface for oxygen-free a-Si:H buffer layer. These improvements can be attributed to the appropriate thickness of the tunnel oxide and confirmed by transmission electron microscopy (TEM) images, to higher crystallinity of the buffer layer, which facilitates more efficient doping in the buffer layer. This is evidenced by energy dispersive Xray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) results. At the device level, a front-side textured, rear-side flat, rear junction poly-SiOx/poly-SiOx solar cell on n-type c-Si wafer, an efficiency improvement can be observed from 3.55 % without a PECVD buffer layer to 18.9 % with an oxygen-free a-Si:H PECVD buffer layer. The impact of the buffer layer crystallinity on cell performance is further demonstrated by deploying a 10-nm thick LPCVD buffer layer, which facilitates an efficiency of 21.15 % for the same device structure.

Sequential thermally evaporated perovskite films with high carrier mobility for efficient p–i–n cell preparation and film scaling-up.

The progress in research and development in the bilateral collaboration between Delft University of Technology and HyET Solar on lightweight and flexible thin-film photovoltaic (PV) foils, will be presented. The PV technologies under development are based on thin-film silicon, perovskites or a hybrid combination of both materials. Advances in terms of performance, reliability and processing of thin film PV foils and materials will be presented. In this contribution we will focus on i) the development of textured substrates to enhance the optical performance of thin-film PV devices, ii) development of bi-layered indium-free transparent conductive oxide (TCOs) to decouple the optical and electrical functionality of the transparent front contact-window layers in thin-film PV devices, iii) volume-deficiency and defect engineering of germanium alloys to realize a low band gap p-i-n junction for multi-junction PV architectures; iv) upscaling the deposition rates of perovskites absorber layers using co-evaporation processing, and v) development of in-house ElectroLuminescence and IR analyses on PV foils as a helpful feedback loop to quickly start up a module production line and optimize its processing steps.

The fabrication process of interdigitated-back-contacted silicon heterojunction (IBC-SHJ) solar cells has been significantly simplified with the development of the so-called tunnel-IBC architecture. This architecture utilizes a highly conductive (p)-type nanocrystalline silicon (nc-Si:H) layer deposited over the full substrate area comprising pre-patterned (n)-type nc-Si:H fingers. In this context, the (p)-type nc-Si:H layer is referred to as blanket layer. As both electrodes are connected to the same blanket layer, the high lateral conductivity of (p)nc-Si:H layer can potentially lead to relatively low shunt resistance in the device, thus limiting the performance of such solar cells. To overcome such limitation, we introduce a thin (<2 nm) full-area molybdenum oxide (MoOx) layer as an alternative to the (p)nc-Si:H blanket layer. We demonstrate that the use of such a thin MoOx minimizes the shunting losses thanks to its low lateral conductivity while preserving the simplified fabrication process. In this process, a novel (n)-type nc-Si:H/MoOx electron collection contact stack is implemented within the proposed solar cell architecture. We assess its transport mechanisms via electrical simulations showing that electron transport, unlike in the case of tunnel-IBC, occurs in the conduction band fully. Moreover, the proposed contact stack is evaluated in terms of contact resistivity and integrated into a proof-of-concept front/back-contacted (FBC) SHJ solar cells. Contact resistivity as low as 100 m Omega cm(2) is achieved, and fabricated FBC-SHJ solar cells obtain a fill factor above 81.5% and open-circuit voltage above 705 mV. Lastly, the IBC-SHJ solar cells featuring the MoOx blanket layer are fabricated, exhibiting efficiencies up to 21.14% with high shunt resistances above 150 k Omega cm(2). Further optimizations in terms of layer properties and fabrication process are proposed to improve device performance and realize the efficiency potential of our novel IBC-SHJ solar cell architecture.

Transition metal oxide (TMO) thin films exhibit large bandgap and hold great potential for enhancing the performance of silicon heterojunction (SHJ) solar cells by increasing the short-circuit current density significantly. On the other hand, achieving precise control over the electrical properties of TMO layers is crucial for optimizing their function as efficient carrier-selective layer. This study demonstrates a general and feasible approach for manipulating the quality of several TMO films, aimed at enhancing their applicability in silicon heterojunction (SHJ) solar cells. The core of our method involves precise engineering of the interface between the TMO film and the underlying hydrogenated intrinsic amorphous silicon passivation layer by managing the reaction of the TMO on the surface. X-ray photoelectron spectroscopy spectra demonstrate that our methods can modify the oxygen content in TMO films, thereby adjusting their electronic properties. By applying this method, we have successfully fabricated WOx-based SHJ solar cells with 23.30 % conversion efficiency and V2Ox-based SHJ solar cells with 22.04 % conversion efficiency, while keeping n-type silicon-based electron-transport layer at the rear side. This research paves the way for extending such interface engineering methods to other TMO materials used as hole-transport layers in SHJ solar cells.

Reducing indium consumption in transparent conductive oxide (TCO) layers is crucial for mass production of silicon heterojunction (SHJ) solar cells. In this contribution, optical simulation‐assisted design and optimization of SHJ solar cells featuring MoOx hole collectors with ultra‐thin TCO layers is performed. Firstly, bifacial SHJ solar cells with MoOx as the hole transport layer (HTL) and three types of n‐contact as electron transport layer (ETL) are fabricated with 50 nm thick ITO on both sides. It is found that bilayer (nc‐Si:H/a‐Si:H) and trilayer (nc‐SiOx:H/nc‐Si:H/a‐Si:H) as n‐contacts performed electronically and optically better than monolayer (a‐Si:H) in bifacial SHJ cells, respectively. Then, as suggested by optical simulations, the same stack of tungsten‐doped indium oxide (IWO) and optimized MgF2 layers are applied on both sides of front/back‐contacted SHJ solar cells. Devices endowed with 10 nm thick IWO and bilayer n‐contact exhibit a certified efficiency of 21.66% and 20.66% when measured from MoOx and n‐contact side, respectively. Specifically, when illuminating from the MoOx side, the short‐circuit current density and the fill factor remain well above 40 mA cm−2 and 77%, respectively. Compared to standard front/rear TCO thicknesses (75 nm/150 nm) deployed in monofacial SHJ solar cells, this represents over 90% TCO reduction. As for bifacial cells featuring 50 nm thick IWO layers, a champion device with a bilayer n‐contact as ETL is obtained, which exhibits certified conversion efficiency of 23.25% and 22.75% when characterized from the MoOx side and the n‐layer side, respectively, with a bifaciality factor of 0.98. In general, by utilizing a n‐type bilayer stack, bifaciality factor is above 0.96 and it can be further enhanced up to 0.99 by switching to a n‐type trilayer stack. Again, compared to the aforementioned standard front/rear TCO thicknesses, this translates to a TCO reduction of more than 67%.

Due to the unique microstructure of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H), the optoelectronic properties of this material can be tuned over a wide range, which makes it adaptable to different solar cell applications. In this work, the authors review the material properties of nc-SiOx:H and the versatility of its applications in different types of solar cells. The review starts by introducing the growth principle of doped nc-SiOx:H layers, the effect of oxygen content on the material properties, and the relationship between optoelectronic properties and its microstructure. A theoretical analysis of charge carrier transport mechanisms in silicon heterojunction (SHJ) solar cells with wide band gap layers is then presented. Afterwards, the authors focus on the recent developments in the implementation of nc-SiOx:H and hydrogenated amorphous silicon oxide (a-SiOx:H) films for SHJ, passivating contacts, and perovskite/silicon tandem devices.

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.

Excellent surface passivation induced by ( i )a‐Si:H is critical to achieve high‐efficiency silicon heterojunction (SHJ) solar cells. This is key for conventional single‐junction cell applications but also for bottom cell application in tandem devices. In this study, we investigated the effects of ( i )a‐Si:H deposition temperature on passivation quality and SHJ solar cell performance. At the lower end of temperatures ranging from 140°C to 200°C, it was observed with Fourier‐transform infrared spectroscopy (FTIR) that ( i )a‐Si:H films are less dense, thus hindering their surface passivation capabilities. However, with additional hydrogen plasma treatments (HPTs), those ( i )a‐Si:H layers deposited at lower temperatures exhibited significant improvements and better passivation qualities than their counterparts deposited at higher temperatures. On the other hand, even though we observed the highest V OC s for cells with ( i )a‐Si:H deposited at the lowest temperature (140°C), the related FFs are poorer as compared to their higher temperature counterparts. The optimum trade‐off between V OC and FF for the SHJ cells was found with temperatures ranging from 160°C to 180°C, which delivered independently certified efficiencies of 23.71%. With a further improved p ‐layer that enables a FF of 83.3%, an efficiency of 24.18% was achieved. Thus, our study reveals two critical requirements for optimizing the ( i )a‐Si:H layers in high‐efficiency SHJ solar cells: (i) excellent surface passivation quality to reduce losses induced by interface recombination and simultaneously (ii) less‐defective ( i )a‐Si:H bulk to not disrupt the charge carrier collections.

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.