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Vacuum-based deposition of optoelectronic thin films has a long-standing history. However, in the field of perovskite-based photovoltaics, these techniques are still not as advanced as their solution-based counterparts. Although high-efficiency vacuum-based perovskite solar cells reaching power conversion efficiencies (PCEs) above 20% are reported, the number of studies on the underlying physical and chemical mechanism of the co-evaporation of lead iodide and methylammonium iodide is low. In this study, the impact of one of the most crucial process parameters in vacuum processes--the substrate material--is studied. It is shown that not only the morphology of the co-evaporated perovskite thin films is significantly influenced by the surface polarity of the substrate material, but also the incorporation of the organic compound into the perovskite framework. Based on these studies, a selection guide for suitable substrate materials for efficient co-evaporated perovskite thin films is derived. This selection guide points out that the organic vacuum-processable hole transport material 2,2�€�,7,7�€�-tet ra(N,N-di-p-tolyl)amino-9,9-spirobifluorene is an ideal candidate for the fabrication of efficient all-evaporated perovskite solar cells, demonstrating PCEs above 19%. Furthermore, building on the insights into the formation of the perovskite thin films on different substrate materials, a basic crystallization model for co-evaporated perovskite thin films is suggested. [ABSTRACT FROM AUTHOR]

High power conversion efficiency (PCE) perovskite solar cells (PSCs) rely on optimal alignment of the energy bands between the perovskite absorber and the adjacent charge extraction layers. However, since most of the materials and devices of high performance are prepared by solution‐based techniques, a deposition of films with thicknesses of a few nanometers and therefore a detailed analysis of surface and interface properties remains difficult. To identify the respective photoactive interfaces, photoelectron spectroscopy measurements are performed on device stacks of methylammonium‐lead‐iodide (MAPI)‐based PSCs in classical and inverted architectures in the dark and under illumination at open‐circuit conditions. The analysis shows that vacuum‐deposited MAPI perovskite absorber layers are n‐type, independent of the architecture and of the charge transport layer that it is deposited on (n‐type SnO2 or p‐type NiOx). It is found that the majority of the photovoltage is formed at the n‐MAPI/p‐HEL (hole extraction layer) junction for both architectures, highlighting the importance of this interface for further improvement of the photovoltage and therefore also the PCE. Finally, an experimentally derived band diagram of the completed devices for the dark and the illuminated case is presented. [ABSTRACT FROM AUTHOR]

An upscalable chemical vapor deposition setup has been built‐up and employed in producing methylammonium lead iodide (MAPI) thin film perovskite solar cells, leading to a maximum efficiency of 12.9%. The method makes use of methylamine gas and hydrogen iodide gas to transform a predeposited layer of lead(II)iodide (PbI2) into MAPI. Although the reaction mechanism includes the intermediate phases lead oxide (PbO) and lead hydroxide (Pb(OH)2), indicated at least on the surface of the samples by XPS, neither species could be observed in XRD measurements of the stepwise reaction, which show a mixture of highly oriented cubic and tetragonal MAPI perovskite lattice systems. [ABSTRACT FROM AUTHOR]

The purpose of this article is twofold. On the one hand the method of spacial resolved photoemission spectroscopy on small angle tapered cross‐sections (TCS) of complete devices is introduced to analyze simultaneously the chemical and electronic structure. On the other hand, a specific working principle of the analyzed cell type is revealed. Solar cells of 18% efficiency are prepared from a single precursor (FAPbI3)0.85(MAPbBr3)0.15 with excess of 15% PbI2. It is shown that TCS‐phototoelectron spectroscopy allows to determine the chemical composition as well as the potential distribution across the full device in the dark and in operation. The energy converting contact is the hole extraction back contact. Interestingly the photopotential in the analyzed cell type is predominantly created within the hole extraction layer and not in the n‐doped perovskite absorber. With the addition of measured core level to valence band maximum positions of the respective layers, TCS line scans lead to the band diagram for the full device. In addition, depth variations of the chemical composition are found: the bromide concentration increases while the iodide concentration is reduced near and within the mesoporous TiO2 layer. [ABSTRACT FROM AUTHOR]

Mater. i B 2021 b , I 31 i , 2104482 The originally published article contains an error in the calculation of the mean free path of methylammonium iodine (MAI) according to equation (2) in the main manuscript (wrong diameter for the MAI molecule), which also resulted in too low values for the mean free path of MAI in Figure 1b and a wrong explanation in the introductory part of the manuscript in section 2.1. Therefore, the conclusion that the loss in the effusive component of the MAI evaporation is due to the increased number of collisions between MAI molecules is unlikely. Most importantly, the influence of the substrate material (here polarity) on the film formation is not influenced by this initially wrong interpretation of our process since the substrate dependency is linked to the interaction of the substrate surface and the condensing molecules in this complex mixed process environment as shown throughout the manuscript. [Extracted from the article]

Using the one‐step flash evaporation technique, it is possible to deposit a film of methylammonium tin iodide (MASI, CH3NH3SnI3) from the solid perovskite powder that is prepared by a mechanochemical synthesis, without the use of any solvents. The source material and the film are characterized by X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD). The XPS measurements show that the MASI film is stoichiometric and is a p‐type material with the Fermi level of 0.4 eV above the valence band maximum (VBM) and a bandgap of 1.3 eV. The XRD pattern of the film reveals the formation of MASI perovskite of high purity, crystallizing with pseudo‐cubic symmetry, having the lattice parameters a ≈ c = 6.239(8) Å. [ABSTRACT FROM AUTHOR]