Controlling the nucleation and crystal growth in solution-processed metal halide perovskite (MHP) thin films is the pivotal point in fabricating homogenous and pinhole-free films. Using scalable coating and printing techniques,...

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 (PEA 2 PbI 4 )/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 PEA 2 PbI 4 /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 PEA 2 PbI 4 /3D methylammonium lead triiodide (MAPbI 3 ) 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.

However, to push the efficiency of this material class further, it is important to understand nonradiative recombination pathways upon photoexcitation under inert conditions as well as in the presence of atmospheric gases. Photoluminescence (PL) quantum efficiency, along with time resolved photoluminescence, provides easy-to-access key parameters that assess the quality of perovskite materials. Such techniques have been adopted by a vast number of groups to study the physical properties of MHP materials of different composition. [5][6][7] Yet, the effect that H 2 O, O 2 , and other gases have on the MHP PL has mostly been investigated under high power illumination with photon flux densities surpassing 10 20 photons s −1 m −2 , i.e., the equivalent of 100 suns and more. [5,6,8] Most of these studies focus on the degradation mechanisms of the material and the long-term stability of devices under diverse environmental conditions. However, the immediate and reversible PL quenching (PLQ) in MHP by different atmospheric molecules, at discrete pressure points and at low excitation densities of 1-10 suns, have not yet been looked at systematically. Given the fact that solar cells mostly operate at such moderate excitation density conditions, it is therefore obligatory to study the ongoing photophysical processes in more detail within this low excitation regime.In this report, we present a systematic study on the nature of second-order PLQ effects of O 2 , N 2 , Ar, and H 2 O on the so-called triple cation perovskite, or CsMAFA, containing cations of cesium, methylammonium (MA), and formamidinium (FA) as well as a mixture of bromide and iodide as anions. CsMAFA was chosen as a model material due to its superior film formation and stability, as opposed to the more common methylammonium lead triiodide (MAPbI 3 ). [9,10] We, however, note that all findings presented here also hold true in MAPbI 3 under low excitation densities. [11] By examining the PL emission and PL lifetimes, second-order quenching processes induced by the tested gas molecules, namely O 2 , N 2 , and Ar, as well as for H 2 O, are investigated quantitatively. The Stern-Volmer (SV) analysis is then applied to PL emission and lifetime measurements at different partial pressures for each gas to identify the nature of the quenching process and the underlaying diffusion kinetics. Metal halide perovskites (MHP), as used in photovoltaic (PV) applications,show a rich photophysics in inert and ambient atmosphere. The presence of atmospheric molecules leads to processes that enhance as well as reduce their photoluminescence (PL) emission. Various phenomena are previously described for a wide variety of gas molecules and different classes of MHP, with a particular interest on the long-term stability for PV applications. However, reversible PL quenching (PLQ) processes, which may be regarded equally important for the performance of PV and other optoelectronic applications, are neglected in other studies. This holds true for O 2 and H 2 O, but especially for low-reacti...

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...

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.