Fabrication of Methylammonium Bismuth Iodide Layers Employing Methylamine Vapor Exposure

Abstract

Methylammonium bismuth iodide (MBI) is a promising candidate for nontoxic perovskite solar cells because of its pronounced stability compared with other lead‐free compounds. Herein, the transformation of solution‐processed BiI3 to MBI employing an exposure to methylamine (MA) vapor is demonstrated. The MA process features a very fast reaction, short process times, and atmospheric‐pressure conditions. The reaction of BiI3 with MA is analyzed and discussed in detail, and the formation of MBI is confirmed via X‐ray diffraction (XRD). Devices based on MA‐treated solution‐deposited BiI3 show performance figures comparable to those of conventionally solution‐processed cells. In conclusion, the results of this study demonstrate that exposure to MA is a promising route toward a fast, versatile, and resource‐efficient production of MA cation based perovskites for solar cell modules.

Engineering Chemical Vapor Deposition for Lead‐Free Perovskite‐Inspired MA3Bi2I9 Self‐Powered Photodetectors with High Performance and Stability

“…X‐ray diffraction (XRD) patterns of films deposited via both types of CVD processes exhibited the typical peaks of the MBI hexagonal perovskite‐derivative structure (space group P6 3 /mmc), manifesting characteristics peaks at 12.6°, 14.5°, 17.1°, 24.6°, 26.7°, 29.1°, 31.7°, and 32.2° (Figure 1e), consistent with previous reports. [ 15–20,25–32 ] No characteristic peaks associated with MAI and BiI 3 peaks were found, confirming the phase purity of the films. The peak with the highest intensity in the XRD pattern of the 1T‐CVD films was located at 24.6°, which corresponds to a (006) orientation.…”

“…To overcome the film morphology limitations reported in the literature on lead‐free bismuth‐based PIMs grown through vapor‐based strategies, [ 25–32 ] in this study we investigated the deposition of MBI using a modified source delivery CVD system. In CVD, the precursors are brought into the vapor phase by heating and are then carried by an inert gas stream to the vicinity of a heated substrate.…”

“…It is worth noting that the 2T‐CVD MBI films exhibited a morphology that is considerably improved compared to the prior literature, which typically reported MBI films with noncompact surface morphologies, disconnected/isolated grains, and a large number of pinholes. [ 15–20,25–32 ] The enhancement in surface morphology of 2T‐CVD MBI films compared to the 1T‐counterparts can be attributed to the efficient delivery of the precursors to the substrate region, as enabled by the separate delivery system used for the two precursors, which would lead to the formation of a laminar flow regime (Figure S2, Supporting Information). Consequently, a homogenous reaction of the precursors would occur at or in the immediate vicinity of the substrate surface, as reflected by the high quality of the resultant MBI films.…”

“…[ 5,21–24 ] Consequently, various strategies have been developed to improve film quality, both using solution‐based methods (e.g., additive‐assisted spin coating; electric‐field‐assisted spray coating; and two‐stage electric‐field‐assisted reactive deposition) and vapor‐based methods (e.g., vapor‐assisted solution process (VASP); chemical vapor deposition (CVD); and thermal evaporation). [ 15–20,25–32 ] Among these methods, multi‐zone CVD is particularly attractive because it allows a robust control of the film growth conditions through the fine‐tuning of the process parameters (i.e., the pressure, gas flow rate, and temperature of the precursors; and the temperature of the substrate). [ 33 ] For instance, CVD has been successfully used for the large‐area deposition of uniform, compact films of lead‐based perovskites.…”

Co-evaporation as an optimal technique towards compact methylammonium bismuth iodide layers

“…Nevertheless, the toxicity is only partially reduced with this method as toxic methylamine gas is used as the organic precursor. Interestingly, additional deposition techniques like electric-field assisted spray coating 21,22 , vapour-assisted solution process (VASP) 23 , or chemical vapour deposition (CVD) 24,25 among others, have been also investigated, providing a record in device efficiency exceeding 3% 23 . However, having homogeneous and conformal coating are still challenging, making it difficult to employ MBI as the real alternative.…”