Noncontact inkjet printing offers rapid and digital deposition combined with excellent control over the layer formation for printed perovskite solar cells. In this work, inkjet printing is used to deposit triple cation perovskite layers with 10% cesium in a mixed formamidinium/methylammonium lead iodide/bromide composite for solar cells with high temperature and moisture stability. A reliable process control over a wide range of perovskite layer thickness from 175 to 780 nm and corresponding grain sizes is achieved by adjusting the drop spacing of the inkjet printer cartridge. A continuous power output at constant voltage, resulting in a power conversion efficiency of 12.9%, is demonstrated, representing a major improvement from previously reported inkjet-printed methylammonium lead triiodide perovskite solar cells. Moreover, this work highlights the extended resistance of triple cation perovskite solar cells against heat and moisture for our ambient inkjet printing approach. The presented results are a proof of concept for the processability of high efficiency perovskite solar cells using digital inkjet printing for next generation photovoltaic applications.

Transferring the high power conversion efficiencies (PCEs) of spin‐coated perovskite solar cells (PSCs) on the laboratory scale to large‐area photovoltaic modules requires a significant advance in scalable fabrication methods. Digital inkjet printing promises scalable, material, and cost‐efficient deposition of perovskite thin films on a wide range of substrates and in arbitrary shapes. In this work, high‐quality inkjet‐printed triple‐cation (methylammonium, formamidinium, and cesium) perovskite layers with exceptional thicknesses of >1 µm are demonstrated, enabling unprecedentedly high PCEs > 21% and stabilized power output efficiencies > 18% for inkjet‐printed PSCs. In‐depth characterization shows that the thick inkjet‐printed perovskite thin films deposited using the process developed herein exhibit a columnar crystal structure, free of horizontal grain boundaries, which extend over the entire thickness. A thin film thickness of around 1.5 µm is determined as optimal for PSC for this process. Up to this layer thickness X‐ray photoemission spectroscopy analysis confirms the expected stoichiometric perovskite composition at the surface and shows strong deviations and inhomogeneities for thicker thin films. The micrometer‐thick perovskite thin films exhibit remarkably long charge carrier lifetimes, highlighting their excellent optoelectronic characteristics. They are particularly promising for next‐generation inkjet‐printed perovskite solar cells, photodetectors, and X‐ray detectors.

application-oriented research like process engineering and upscaling is observed. [1][2][3][4][5] Even though other optoelectronic devices like light emitting diodes and lasers are being researched, [6][7][8][9][10][11][12][13] perovskite-based photovoltaics (PV) is the key technology driving the fast emergence of perovskitebased optoelectronics. Recently, power conversion efficiencies (PCEs) close to 24% were demonstrated for perovskite PV, exceeding the PCEs of established thinfilm technologies. [14] Despite the rapid progress in terms of PCE, one key challenge of perovskite-based PV is still its low stability under realistic outdoor stress conditions-temperature, humidity, and ultraviolet (UV) radiation. A significant advance toward more stable devices was demonstrated by engineering the composition of the large cation site of the perovskite crystal structure and by including low-dimensional perovskite interlayers and passivation layers. [15][16][17][18][19][20] Further advances in stability are based on the charge extracting materials and their interfaces with the perovskite absorber layers. [21][22][23] Most reported record PCEs are still based on highly expensive organic hole transport layer (HTL) materials like 2,2′,7,7′-tetrakis[N,N-di (4methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-MeOTAD) or poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). [20,24,25] Although these materials result in good performance on short High-quality charge carrier transport materials are of key importance for stable and efficient perovskite-based photovoltaics. This work reports on electron-beam-evaporated nickel oxide (NiO x ) layers, resulting in stable power conversion efficiencies (PCEs) of up to 18.5% when integrated into solar cells employing inkjet-printed perovskite absorbers. By adding oxygen as a process gas and optimizing the layer thickness, transparent and efficient NiOx hole transport layers (HTLs) are fabricated, exhibiting an average absorptance of only 1%. The versatility of the material is demonstrated for different absorber compositions and deposition techniques. As another highlight of this work, all-evaporated perovskite solar cells employing an inorganic NiO x HTL are presented, achieving stable PCEs of up to 15.4%. Along with good PCEs, devices with electron-beam-evaporated NiO x show improved stability under realistic operating conditions with negligible degradation after 40 h of maximum power point tracking at 75 °C. Additionally, a strong improvement in device stability under ultraviolet radiation is found if compared to conventional perovskite solar cell architectures employing other metal oxide charge transport layers (e.g., titanium dioxide). Finally, an all-evaporated perovskite solar mini-module with a NiO x HTL is presented, reaching a PCE of 12.4% on an active device area of 2.3 cm 2 .

optoelectronic devices, a novel lowcost and highly efficient photovoltaic (PV) material emerged. Only 10 years after the first reported perovskite solar cells (PSCs), power conversion efficiencies (PCEs) above 23% were certified, exceeding those of much longer established thin-film PV technologies, including organic photovoltaics (OPV) and inorganic thin-film PV based on copper indium gallium selenide (CIGS) or cadmium telluride (CdTe). [1] The material class of hybrid organic-inorganic perovskites combines excellent optoelectronic properties, such as long diffusion lengths [2] and short absorption lengths, [3] with the ease of solution processing, low energy payback times, and low-cost precursor materials. [4] Moreover, the optoelectronic properties and the material stability can be engineered by varying the constituents in the perovskite crystal structure ABX 3 . For example, the bandgap (E G ) can be tuned by changing the stoichiometric ratio of Br and I at the halogen anion site X. [5][6][7] In order to improve the stability of hybrid organic-inorganic perovskites, compositional engineering of the cation site A was demonstrated to be successful via combining methylammonium (CH 3 NH 3 + or MA + ), formamidinium (CH 5 N 2 + or FA + ), Cs + , and Rb + ions in the so-called multi-cation perovskites. [8][9][10][11] Three key challenges hinder today the economical breakthrough of PSCs:Stability: First, the instability of PSCs against moisture, oxygen, light, and temperature limits the lifetime of PSCs to a fraction of the warranty lifetime (often >25 years) of the market dominating crystalline silicon (c-Si) PV. [12] Very respectable progress has been made over recent years to enhance the stability of PSCs by demonstrating stability over 1000 h, but significant further advances in terms of stability are needed to lift the technology to a level where it is ready to compete with, or be a bolt-on tandem companion to the current PV heavyweight of c-Si. A number of reviews cover recent developments on the topic of stability. [13][14][15][16][17] Toxicity: Second, highly efficient PSCs still contain lead, the toxicity of which hampers the acceptance of the technology and could conflict with legislative barriers. [18] Other recent reviews present progress with respect to this challenge. [19,20] Upscaling: Third, the upscaling of perovskite PV devices to commercial PV module sizes (>1 m 2 ) must be achieved. To date, the vast majority of research and development of PSCs is still Hybrid organic-inorganic metal halide perovskite semiconductors provide opportunities and challenges for the fabrication of low-cost thin-film photovoltaic devices. The opportunities are clear: the power conversion efficiency (PCE) of small-area perovskite photovoltaics has surpassed many established thin-film technologies. However, the large-scale solution-based deposition of perovskite layers introduces challenges. To form perovskite layers, precursor solutions are coated or printed and these must then be crystallized into the perovskite structur...