Roja Singh

Vapor phase deposition methods are readily able to achieve uniform coverage of large‐area substrates and are widely considered promising for industrial‐scale perovskite solar cell fabrication. However, as perovskite‐silicon tandem solar cells approach commercialization, practical considerations of manufacturing throughput come into play. Here, it is shown that the inherent sublimation characteristics of the organic precursor formamidinium iodide (FAI) make increasing the deposition rate of FA‐based co‐evaporated perovskites negatively impact replicability and lead to a substantial decrease in power conversion efficiency (PCE). These losses are linked to reduced film homogeneity and the emergence of carbon‐rich regions within the perovskite layer. To mitigate these rate‐induced effects, two approaches are explored: source layout optimization and material preconditioning. Utilizing dual FAI sources rather than a single FAI source reduces the relative PCE drop from ≈23% _rel to ≈9% _rel at a deposition rate of ≈18 nm min ⁻¹ (14.8% PCE @ maximum power point (MPP)) compared to the baseline rate of 5 nm min ⁻¹ (16.2% PCE @MPP). Alternatively, preconditioning a single FAI source reduces the performance losses from ≈31% _rel to ≈26% _rel at a deposition rate of ≈21 nm min ⁻¹ . These findings underscore the importance of tailored source strategies to enable high‐rate FA‐based co‐evaporated perovskites without compromising device performance.

Established sequential deposition of multilayer two-terminal (2T) all-perovskite tandem solar cells possesses challenges for fabrication and limits the choice of materials and device architecture. In response, this work represents a lamination process based on a transparent and conductive adhesive that interconnects the wide-bandgap (WBG) perovskite top solar cell and the narrow-bandgap (NBG) perovskite bottom solar cell in a monolithic 2T all-perovskite tandem solar cell. The transparent conductive adhesive (TCA) layer combines Ag-coated poly(methyl methacrylate) microspheres with an optical adhesive. The TCA is employed as a recombination junction, achieving self-encapsulation with high transparency and good conductivity. A high vertical electrical conductivity is realized by optimizing the distribution of microspheres using a novel solidification strategy that employs UV curing and drying at 85 °C at low pressure. In addition, uniform and dense bilayer hole transport layers are realized by vapor-phase evaporation, which facilitates the application of the TCA and achieves pinhole-free buried interfaces in both the WBG perovskite top solar cell and the NBG perovskite bottom solar cell. Using these two strategies, losses in fill factor (FF) and open-circuit voltage (V_OC) of the 2T all-perovskite tandem solar cell are reduced, achieving a respectable power conversion efficiency up to 18.2% for the lamination of the all-perovskite tandem solar cell. The laminated tandem solar cell retains ∼93% of initial efficiency after exposure in ambient air (30-70 RH% and 20-35 °C) for ∼30 days.

Enhancing reproducibility, repeatability, as well as facilitating transferability between laboratories will accelerate the progress in many material domains, wherein perovskite-based optoelectronics are a prime use case. This study presents fully automated perovskite thin film processing using a commercial spin-coating robot in an inert atmosphere. We successfully apply this novel processing method to antisolvent quenching. This process is typically difficult to reproduce and transfer and is now enhanced to exceptional repeatability in comparison to manual processing. Champion perovskite solar cells demonstrate power conversion efficiencies as high as 19.9%, proving the transferability of established manual spin-coating processes to automatic setups. Comparison with human experts reveals that the performance is already on par, while automated processing yields improved homogeneity across the substrate surface. This work demonstrates that fully automated perovskite thin film processing improves repeatability. Such systems bear the potential to become a foundation for autonomous optimization and greatly improve transferability between laboratories.

The long-term stability of perovskite solar cells (PSCs) remains a bottleneck for commercialization. While studies on the stoichiometry and morphology of PSCs with regard to performance are prevalent, understanding the influence of these factors on their long-term stability is lacking. In this work, we evaluate the impact of stoichiometry and morphology on the long-term stability of cesium formamidinium-based PSCs. We demonstrate that the lead iodide (PbI₂) to formamidinium iodide (FAI) ratio influences stability under various stress factors (elevated temperature and light). A high molar ratio (PbI₂/FAI > 1.1) in the perovskite precursor displays drastic degradation under ISOS-L1 (100 mW/cm², 25 °C, maximum power point tracking) conditions. However, postdegradation analysis contradicts these results. Devices with PbI₂/FAI ≤ 1.1 are stable under light, but intermittent current density-voltage characterizations indicate that device performance decreases during storage in the dark. Migration of iodide (I^-) ions to the electron-transport layer (ETL) and iodine vacancies (V_I-⁺) to the hole-transport layer (HTL) forms localized shunts in the absorber layer. Pinhole formation, surrounded by FA⁺-rich regions, explains the extent of damage in comparably aged films. In summary, this work emphasizes the importance of reporting stability under different stress conditions, coupled with postdegradation and dark recovery analyses of PSCs to better understand the complexities of perovskite instability under real-life conditions such as expected during outdoor operation.

Optical interference filters (OIFs) are vital components for a wide range of optical and photonic systems. They are pivotal in controlling spectral transmission and reflection upon demand. OIFs rely on optical interference of the incident wave at multilayers, which are fabricated with nanometer precision. Here, we demonstrate that these requirements can be fulfilled by inkjet printing. This versatile technology offers a high degree of freedom in manufacturing, as well as cost-affordable and rapid-prototyping features from the micron to the meter scale. In this work, via rational ink design and formulation, OIFs were fully inkjet printed in ambient conditions. Longpass, shortpass, bandpass, and dichroic OIFs were fabricated, and precise control of the spectral response in OIFs was realized. Subsequently, customized lateral patterning of OIFs by inkjet printing was achieved. Furthermore, upscaling of the printed OIFs to A4 size (29.7 × 21.0 cm²) was demonstrated.

Over the past decade, the impressive progress in power conversion efficiency (PCE) of organometallic halide perovskite solar cells (PSCs), coupled with their ready integration into tandem solar cells, has led them to approach PCEs of 30% for tandem solar cells with a silicon bottom subcell. However, the complementary technology of perovskite/copper indium gallium selenide (CIGS) tandem solar cells has been thus far unable to reach similar efficiency values. Herein, a further advance in the efficiency of 4T perovskite/CIGS tandems is demonstrated, increasing the PCE up to 27.3% via systematic optimization of the top semitransparent PSC. Improvements in light management through the optimization of anti‐reflection coatings, coupled with the development of transparent conductive oxides that incur very low parasitic absorption are reported. It is revealed that both are crucial for maximizing efficiency and, by utilizing additional optical simulations, a detailed loss analysis that enables us to outline a path toward approaching 30% PCE for 4T perovskite/CIGS tandem devices is developed.

Monolithic all-perovskite tandem photovoltaics promise to combine low-cost and high-efficiency solar energy harvesting with the advantages of all-thin-film technologies. To date, laboratory-scale all-perovskite tandem solar cells have only been fabricated using non-scalable fabrication techniques. In response, this work reports on laser-scribed all-perovskite tandem modules processed exclusively with scalable fabrication methods (blade coating and vacuum deposition), demonstrating power conversion efficiencies up to 19.1% (aperture area, 12.25 cm²; geometric fill factor, 94.7%) and stable power output. Compared to the performance of our spin-coated reference tandem solar cells (efficiency, 23.5%; area, 0.1 cm²), our prototypes demonstrate substantial advances in the technological readiness of all-perovskite tandem photovoltaics. By means of electroluminescence imaging and laser-beam-induced current mapping, we demonstrate the homogeneous current collection in both subcells over the entire module area, which explains low losses (rel) in open-circuit voltage and fill factor for our scalable modules.

Monolithic two-terminal (2T) perovskite/CuInSe₂ (CIS) tandem solar cells (TSCs) combine the promise of an efficient tandem photovoltaic (PV) technology with the simplicity of an all-thin-film device architecture that is compatible with flexible and lightweight PV. In this work, we present the first-ever 2T perovskite/CIS TSC with a power conversion efficiency (PCE) approaching 25% (23.5% certified, area 0.5 cm²). The relatively planar surface profile and narrow band gap (∼1.03 eV) of our CIS bottom cell allow us to exploit the optoelectronic properties and photostability of a low-Br-containing perovskite top cell as revealed by advanced characterization techniques. Current matching was attained by proper tuning of the thickness and bandgap of the perovskite, along with the optimization of an antireflective coating for improved light in-coupling. Our study sets the baseline for fabricating efficient perovskite/CIS TSCs, paving the way for future developments that might push the efficiencies to over 30%.