Substoichiometric Mixing of Metal Halide Powders and Their Single-Source Evaporation for Perovskite Photovoltaics

Abstract

High-vacuum, single-source thermal evaporation is an appealing deposition process for perovskite photovoltaics. It promises the homogeneous and precisely controlled growth of very pure and homogeneous films on large areas in a conformal way. In this work, we study mechanically synthesized substoichiometric cesium bromide−lead iodide precursors, the single-source evaporation of the resulting mixes, subsequent deposited metal halide thin films, and converted perovskite thin films. Diffraction pattern analysis reveals the absence of new phases formed during ball-milling. Using synchrotron in situ grazing-incidence wide-angle X-ray scattering and energy-dispersive X-ray spectroscopy, we demonstrate that halide exchange between precursors occurs during the evaporation process. It is also found that a higher cesium bromide content results in films with more impurities. The proof-of-concept photovoltaic devices with the optimized cesium bromide content reach an efficiency of 15% for an optical bandgap of 1.7 eV.

Advancing high-throughput combinatorial aging studies of hybrid perovskite thin films via precise automated characterization methods and machine learning assisted analysis

“…These findings are in agreement with previous results from synchrotron-based Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) measurements on two-step deposited MHPs grown from thermally evaporated templates. 47,48 As a result of the differences in texture between the two phases, determination of the phase fraction from the 2 Θ scans alone would result in an underestimation of the MHP phase ratio compared to PbI 2 . To account for this effect, the normalized peak area A norm is first calculated according to:where A 2 Θ denotes the peak area obtained from the 2 Θ measurement, A χ denotes the area under curve for the χ scan performed at the given reflection and I χ =0° denotes the absolute intensity at χ = 0°.…”

Quantifying Organic Cation Ratios in Metal Halide Perovskites: Insights from X-ray Photoelectron Spectroscopy and Nuclear Magnetic Resonance Spectroscopy

“…Mechanochemical synthesis has been used to synthesize MHP powders that were later used for the fabrication of MHP films via solution ,, or different vapor-phase growth methods. − Among single-source PVD methods, pulsed laser deposition (PLD) ,− and sputtering deposition , utilize solid targets consisting of mixtures of the MHP precursors. Previously, we demonstrated the critical role of the MHP target composition (including an 8-fold excess of organic cations compared to inorganic components) in determining the final film’s stoichiometry and optoelectronic properties during PLD. , Therefore, a precise compositional characterization of both targets and thin films is essential for enhancing the reproducibility of PVD film fabrication.…”

Pizza Oven Processing of Organohalide Perovskites (POPOP): A Simple, Versatile and Efficient Vapor Deposition Method

“…More details on the metallic template vapor deposition are available in the methods section, and extensive characterization of our co-evaporated template has been reported in another study. [17] The only change detected in the thin films after the process is a strong presence of NH 4 I. Suspecting the transport pipes as the origin of the lack of conversion, we reduced the pipe path from the evaporator to the reaction chamber (Figure S3, Supporting Information). This approach enabled the formation of FA-perovskites, albeit still limited by a long process duration and residual presence of NH 4 I.…”