Large area inkjet-printed metal halide perovskite LEDs enabled by gas flow assisted drying and crystallization

We demonstrate the upscaling of inkjet-printed metal halide perovskite light-emitting diodes. To achieve this, the drying process, critical for controlling the crystallization of the perovskite layer, was optimized with an airblade-like slit nozzle in a gas flow assisted vacuum drying step. This yields large, continuous perovskite layers in light-emitting diodes with an active area up to 1600 mm2.Peer Reviewe

The Electronic Properties of a 2D Ruddlesden‐Popper Perovskite and its Energy Level Alignment with a 3D Perovskite Enable Interfacial Energy Transfer

The success of using 2D Ruddlesden-Popper metal halide perovskites (MHPs) in optoelectronic devices has ignited great interest as means for energy level tuning at the interface with 3D MHPs. Inter alia, the application of 2D phenylethylammonium lead quaternary iodide (PEA2PbI4)/3D MHPs interfaces has improved various optoelectronic devices, where a staggered type-II energy level alignment is often assumed. However, a type-II heterojunction seems to contradict the enhanced photoluminescence observed for 2D PEA2PbI4/3D MHP interfaces, which raises fundamental questions about the electronic properties of such junctions. In this study, using direct and inverse photoelectron spectroscopy, it is revealed that a straddling type-I energy level alignment is present at 2D PEA2PbI4/3D methylammonium lead triiodide (MAPbI3) interfaces, thus explaining that the photoluminescence enhancement of the 3D perovskite is induced by energy transfer from the 2D perovskite. These results provide a reliable fundamental understanding of the electronic properties at the investigated 2D/3D MHP interfaces and suggest careful (re)consideration of the electronic properties of other 2D/3D MHP heterostructures.Peer Reviewe

Electrospun Electroluminescent CsPbBr3 Fibers as Flexible Perovskite Networks for Light‐Emitting Application

Thin-film perovskite light-emitting diodes have gained increasing attention in the last 6 years. With the possibility to process the emitting layer from solution, the way for 1D morphology of the semiconductor for flexible devices is paved. Herein, for the first time single-step fabrication of CsPbBr3@PVP nanofibers in a customized electrospinning process performed under ambient conditions from a water-based precursor solution is reported. The water-based approach allows the incorporation of a conductive polymer into the compound fiber by blending the perovskite precursor ink with commercially available PEDOT:PSS dispersion. The results demonstrate electrospun fiber mats which are stable at ambient conditions for at least 5 months and can be utilized in electroluminescence devices. Photoluminescence studies on the perovskite fibers reveal a blueshift of the emission peak compared to thin films possibly due to the generation of nanocrystals of ≈12 nm by in situ nanocrystal pinning as confirmed by transmission electron microscopy. A proof-of-concept electrically pumped light-emitting device is built with the obtained fiber mat. The perovskite nanofibers offer promising applications in flexible and stretchable optoelectronics.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Universität zu Köln http://dx.doi.org/10.13039/501100008001Peer Reviewe

Metal Halide Perovskites: Photophysics and Inkjet Printing of Solar Cells

Metallhalogenid-Perowskite (MHPs) sind Halbleiter, die einzigartige photophysikalische Eigenschaften aufweisen, die sie ideal für photovoltaische Anwendungen machen. Techniken werden kontinuierlich entwickelt, um die Leistungsgrenzen der Perowskite weiter zu verschieben. Dennoch weisen diese Materialien verschiedene Herausforderungen auf. Zu diesen gehören eine geringe Stabilität unter einer Vielzahl von äußeren Bedingungen, sowie eine große Diskrepanz zwischen den Wirkungsgraden von Geräten im Labormaßstab und großflächigen Geräten. Zunächst wurden mit Hilfe von Photolumineszenz-Spektroskopie Ladungsübertragungsmechanismen zwischen MHPs und atmosphärischen Gasen untersucht, um deren Einfluss auf die Materialstabilität zu bestimmen. Durch den Vergleich der Emission von verschiedene MHP wurde die Wirkung untersucht, die atmosphärische Gase auf Grenzdefekte im Material haben. Diese Löschungseffekte wurden nachfolgend mit dem Stern-Volmer-Modell analysiert. Es stellte sich heraus, dass ein Teil von der Gase bindet jedoch an die MHPs, wobei teilweise Kristalldefekte passiviert werden und für jedes der Gase Ladungstransfermechanismen vorgeschlagen wurden. Zweitens wurde die Skalierung von MHP-Bauelementen mittels Tintenstrahldruck untersucht. Dazu wurden drei Kristallisationstechniken ausgewertet. Eine davon verwendete eine sequenzielle Abscheidung von zwei Präkursortinten, während die beiden anderen kristallisierte Tinten verwendeten, die in einem Schritt abgeschieden wurden. Die letztgenannten Techniken verwendeten beide niedrige Drücke und bei einer wurde ein kontrollierter Stickstoffstrom auf die Probe angewendet. Solarzellen mit einer Effizienz von 16,8% auf einer Fläche von 0,16 cm² wurden demonstriert. Diese Ergebnisse zeigen ein neuartiges Verfahren zur Untersuchung von strahlungslosen Verlustwegen in MHPs auf. Zusätzlich demonstrieren diese Studien, dass der Tintenstrahldruck eine geeignete Technologie ist, um MHP-Bauelemente zu skalieren.Metal halide perovskites (MHPs) are semiconductor materials that show unique photophysical properties, making them ideal for photovoltaic applications. Having shown power conversion efficiencies of up to 25.5%, techniques are continuously being developed to push perovskites to unprecedent limits. Yet, these materials present challenges like a low stability under a variety of conditions as well as a large disparity between the efficiencies of lab scale and large area devices. This thesis addresses these two major obstacles. First, charge transfer mechanisms between MHPs and atmospheric gases were studied to determine their effect on the material stability by using photoluminescence spectroscopy. By comparing the emission of MHPs, the effect that molecular oxygen, nitrogen, argon, and water have on boundary defects in the material was studied. These quenching effects were later analyzed using the Stern-Volmer model. It was found that the gases bounce off the surface, but a portion of them bind to the MHPs, in occasions passivating defects on the crystals. Using these results, charge transfer mechanisms were proposed for each one of the gases. Second, scaling of MHP devices was examined using inkjet printing. For this, three crystallization techniques were evaluated. One of them used sequential deposition of two precursor inks, while the other two crystallized ink that was deposited in one step. Both latter techniques used low pressures, below 1 mbar, and only one of them applied a controlled stream of nitrogen to the sample. Using these techniques, the deposition of a 15x15 cm² area as well as a device with an efficiency of 16.8% on an area of 0.16 cm² were demonstrated. These results show a novel procedure to study non-radiative loss paths in MHPs to enhance their stability and performance as devices. Also, they show that inkjet printing is a favorable technology to scale MHP devices and eventually facilitate the mass production of this type of photovoltaic devices