Vapor phase deposition of perovskites is often considered a suitable deposition method for uniform deposition on large-area substrates with minimal upscaling losses. For this reason, it is assumed to be suitable for industrial-scale perovskite deposition. However, concerns regarding their practical deposition rates have entered the discourse, since deposition rates of ~1000 nm.min^-1 are typically considered necessary for the technology to be commercially viable. This is of particular concern for co-evaporation of perovskites, which is one of the most common vapor-based fabrication techniques, with typical deposition rates of 6 – 10 nm.min^-1 reported in literature.[1] Some research into MAPbI₃ has aimed to increase deposition speed without compromising device power conversion efficiency (PCE), achieving maximum deposition rates of ~26 nm.min^-1.[2,3] However, there has been no such research on formamidinium (FA)-based perovskites, or for wide bandgap perovskites suitable for tandem applications. A significant reason for this deficit is the propensity of FA to decompose at high temperatures, such as those required for elevated deposition rates, and a lack of understanding how this will impact device PCE.[4]

              In response, we present the first attempt to significantly increase FA-based perovskite deposition speed and analyze the impact of increasing deposition rate on device PCE. Our investigation reveals a negative correlation between deposition rate of FA based co-evaporated perovskites and device power conversion efficiency. Furthermore, high deposition rates will also negatively impact process repeatability. On a device level, the cause of these PCE drops are the emergence of μm-scale inhomogeneities in our perovskite film. Our investigation explores the root cause of these inhomogeneities, demonstrating that they are not the result of the classical degradation products of FAI, which we demonstrate using in situ mass spectrometry. Instead, temperature variations within the residual crucible material leads to the formation of coke products, which are subsequently deposited onto the perovskite as spit defects. 

              During our investigation, we analyzed multiple solutions to improve sample homogeneity and reduce PCE losses when increasing deposition rate, separated into two independent approaches. The first approach utilizes vertical scaling methods, which reduces the loss in PCE from ~23%_rel to ~9%_rel for devices with a ~18 nm.min^-1 deposition rate compared to a baseline of 5 nm.min^-1. The second approach utilizes preconditioning, reducing PCE loss from ~31%_rel to ~26%_rel for devices with ~21 nm.min^-1 deposition rate compared to a baseline 6 nm.min^-1. Our work represents the first attempt to meaningfully increase FA-based wide bandgap perovskite deposition rate while maintaining high efficiency and will facilitate future developments in this field.