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 Cs_xFA_1-xPb(I_1-xBr_x)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.

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.

The monolithic integration of perovskite top cells on textured crystalline silicon affords efficient tandem devices with strong prospects for large-scale applications. Such integration has primarily relied on state-of-the-art recombination junctions, which typically comprise transparent conductive oxides and molecular self-assembled monolayer (SAM) contacts. However, the potential influence of bottom cell nanoroughness, which may vary based on specific processing routes and technologies, has received far less attention. Here, we systematically engineered the top surface nanoroughness of silicon heterojunction solar cells to examine its impact on monolithic perovskite–silicon tandem solar cells. We employed two approaches: (i) varying the thickness of (n)-type hydrogenated nanocrystalline silicon ((n)nc-Si:H) layers or (ii) applying a plasma treatment using a hydrogen and carbon dioxide gas mixture before the deposition of (n)nc-Si:H layers. Both methods enhanced the conductivity and crystallinity of (n)nc-Si:H layers and increased the surface nanoroughness, with plasma treatment enabling the efficient realization of distinct nanoroughness in thin (n)nc-Si:H (15-nm-thick) layers. Our results reveal that the surface nanoroughness imposed by (n)nc-Si:H layers influences the SAM anchoring, leading to increased work function shifts and improved SAM/perovskite interface quality, thereby impacting the overall tandem device performance. Notably, tandem devices incorporating higher-nanoroughness bottom cells achieved increased fill factors, dominating the observed tandem efficiency enhancements, with a peak efficiency of 32.6% enabled by a 30-second-long plasma treatment.

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-SiO_x) layers are developed. However, challenges persist in achieving excellent surface passivation for boron-doped poly-SiO_x 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 10-nm thick intrinsic hydrogenated amorphous silicon buffer layer with varying oxygen content (a-Si (O_x):H) deposited by plasma-enhanced chemical vapor deposition (PECVD), and placed between the tunneling silicon oxide (SiO_x) and the poly-SiO_x (p⁺). After the hydrogenation step, we obtain both high passivation quality with implied open circuit voltage (iV_oc) of 728.3 mV and low contact resistivity (ρ_c) of 59.18 mΩ 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 X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) results. At the device level, a front-side textured, rear-side flat, rear junction poly-SiO_x/poly-SiO_x 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.

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 MoO_x hole collectors with ultra-thin TCO layers is performed. Firstly, bifacial SHJ solar cells with MoO_x 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-SiO_x: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 MoO_x and n-contact side, respectively. Specifically, when illuminating from the MoO_x 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 MoO_x 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-SiO_x: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-SiO_x:H and the versatility of its applications in different types of solar cells. The review starts by introducing the growth principle of doped nc-SiO_x: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-SiO_x:H and hydrogenated amorphous silicon oxide (a-SiO_x:H) films for SHJ, passivating contacts, and perovskite/silicon tandem devices.

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 WO_x-based SHJ solar cells with 23.30 % conversion efficiency and V₂O_x-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.

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 (MoO_x) layer as an alternative to the (p)nc-Si:H blanket layer. We demonstrate that the use of such a thin MoO_x 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/MoO_x 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 mΩcm² 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 MoO_x blanket layer are fabricated, exhibiting efficiencies up to 21.14% with high shunt resistances above 150 kΩcm². 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.

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.

Nonequal current generation in the cells of a photovoltaic module, e.g., due to partial shading, leads to operation in reverse bias. This quickly causes a significant efficiency loss in perovskite solar cells. We report a more quantitative investigation of the reverse bias degradation. Various small reverse biases (negative voltages) were applied for different durations. After normalizing the applied voltages with the breakdown voltages, we found similar dependences of the reverse bias current and the degradation rate. We draw conclusions regarding possible degradation mechanisms and propose a way to increase the comparability of degradation rates for comparing different perovskite solar cells.

Multiple-source thermal evaporation is emerging as an excellent technique to obtain perovskite (PVK) materials for solar cell applications due to its solvent-free processing, accurate control of stoichiometric ratio, and potential for scalability. Nevertheless, the currently reported layer-by-layer deposition approach is afflicted by long processing times caused by the multiple repetitions of thin films, which hinder industrial uptake. On the other hand, the coevaporation entails higher complexity due to the challenges of controlling the sublimation of multiple sources simultaneously. In this work, we propose a simplified approach consisting of a single-cycle deposition (SCD) of three thick precursor layers to obtain high-quality Cs0.15FA0.85PbI2.85Br0.15 (CsFAPbIBr) films. After annealing, the optimized PVK film exhibits comparable properties to the one deposited by multicycle deposition in terms of crystal structure, in-depth uniformity, and optoelectrical properties. Also, the formation and evolution of SCD PVK during annealing are investigated. We found that, in the competitive processes of precursor diffusion and reaction, the presence of cesium bromide can assist precursor mixing driven by the annealing treatment, demonstrating a reaction-limited process in the PVK conversion. With this simplified SCD approach, a PVK film is obtained with expected optical and opto-electronic properties, providing an appealing way for future thermally evaporated PVK device preparation.

Silicon heterojunction (SHJ) solar cells have achieved a record efficiency of 26.81% in a front/back-contacted (FBC) configuration. Moreover, thanks to their advantageous high V_OC and good infrared response, SHJ solar cells can be further combined with wide bandgap perovskite cells forming tandem devices to enable efficiencies well above 33%. In this study, we present strategies to realize high-efficiency SHJ solar cells through combined theoretical and experimental studies, starting from the optimization of Si-based thin-film layers to the implementation of electrodes with reduced indium and silver usage. Advanced opto-electrical simulations, which enable comprehensive theoretical understandings of the main physical mechanisms governing carriers’ collection and light management, provide clear pathways for device designs and experimental optimizations. We present the fabricated FBC-SHJ solar cells in both monofacial and bifacial configurations with the best efficiencies of 24.18% and 23.25%, respectively. We point out that to achieve optimum device performance, the compositional materials should be holistically optimized and evaluated as part of the contact stacks with adjacent layers. As an outlook beyond the classical FBC-SHJ solar cell architecture, we propose various novel SHJ-based solar cell architectures. Their potential performance was assessed and compared via rigorous opto-electrical simulations and a maximal efficiency of 27.60% was simulated for FBC-SHJ solar cells featuring localized contacts.

Passivating contacts are crucial for realizing high-performance crystalline silicon solar cells. Herein, contact formation by plasma-enhanced chemical vapor deposition (PECVD) followed by an annealing step is focused on. Poly-SiO_x passivating contacts by combining plasma-assisted N₂O-based oxidation of silicon (PANO-SiO_x) with a thin film of phosphorus (n⁺) or boron (p⁺)-doped hydrogenated amorphous silicon oxide (a-SiO_x:H) are manufactured. Postannealing is conducted for transitioning a-SiO_x:H into poly-SiO_x. The aim is to achieve a contact with low absorption and high-quality passivation. It is demonstrated that by tuning the plasma oxidation process time and power, the PANO-SiO_x thickness and its passivation quality can be controlled. A higher SiO₂ content is observed in PANO-SiO_x than in the nitric acid oxidation of silicon (NAOS-SiO_x) counterpart. PANO-SiO_x acts as a stronger diffusion barrier for both boron and phosphorus atoms compared to NAOS-SiO_x, affecting the dopant distribution during annealing. Implied open-circuit voltages up to 751 and 710 mV for n⁺ and p⁺ flat symmetric samples, respectively, are demonstrated. With respect to standard thermally grown SiO₂ tunneling oxide combined with (in/ex)situ-doped low-pressure chemical vapor deposition poly-Si, this study presents a simple alternative for manufacturing passivating contact fully based on PECVD processes.