Sn-based perovskites offer lower lead content but face a major challenge: Sn²⁺ oxidizes readily, which has led most research groups to use gloveboxes and chemical additives during processing. Here, we investigate whether precursor molarity alone can mitigate this oxidation problem in ambient air. MAPb_0.75Sn_0.25I₃ solar cells with mesoporous N–i–P architecture were prepared from 1.0 M and 0.9 M solutions by spin-coating with ethyl acetate antisolvent, under standard lab conditions (28–34 °C, 30–45% RH). The characterization included SEM, XRD, XPS, profilometry, and J–V measurements. The 0.9 M concentration produced thinner films (275 nm vs. 474 nm), better Sn²⁺/Sn⁴⁺ ratios (16.5%/83.5% vs. 77.6%/22.4% by XPS), lower band gaps (1.51–1.52 vs. 1.55–1.56 eV), and larger grains. Device efficiency increased from 1.61 ± 0.68% (1.0 M) to 4.53 ± 0.91% (0.9 M), with the best cell reaching 5.91%—about 85% of our MAPbI₃ control (6.96%). After one month of storage, 0.9 M cells retained 61% efficiency compared to 37% for 1.0 M devices. These findings demonstrate that a simple reduction in precursor molarity can substantially suppress Sn⁴⁺ formation during ambient fabrication, providing a practical route for laboratories without controlled atmospheres.

The transition from small-area and atmosphere-controlled spin-coating to large-area bar coating in an uncontrolled ambient process requires a comprehensive understanding of the crystallization kinetics in perovskite precursor layers. In this work, we investigate the structural, optical, and photovoltaic properties of additive-free methylammonium lead triiodide (MAPbI3) films fabricated via bar coating without a glove box. We analyze these properties as a function of the precursor solvent system, plate temperature, and bar groove depth. The solvent strategy employs a mixture of 2-methoxyethanol (2ME), acetonitrile (ACN), and N-methyl-2-pyrrolidone (NMP) to regulate nucleation and growth at low processing temperatures (24–50 °C). Our findings indicate that the volumetric ratios of the solvent components and the plate temperature are critical in determining crystallinity, optical homogeneity, and film compactness. In contrast, the bar groove depth primarily modulates film morphology and compactness, with a less pronounced effect on the material’s intrinsic structural or optical properties. By optimizing the synergy between solvent chemistry and physical coating parameters, the power conversion efficiencies (PCE) were enhanced from 7 to 11.85% under relative humidity >35%. This study establishes a processing protocol that may facilitate future scale-up of bar-coated perovskite films.

This study presents the use of hyperspectral imaging (HSI) as a non-destructive technique for analyzing degradation pathways in MAPbI3-xClx perovskite films. The films have been fabricated under ambient laboratory conditions (relative humidity > 40%, without a glovebox and) by spin coating and bar coating, with areas of 6.25 and 25 cm2 respectively. Over a 16-week monitoring period, spatially and spectrally resolved HSI data has been used to establish a correlation between perovskite quality and changes in optical transmittance across the 450-975 nm spectral range. The results indicate that the degradation process can be classified into three distinct states: (I) a pristine state dominated by the MAPbI3-xClx spectral response, (II) an intermediate state characterized by reduced light absorption due to partial perovskite conversion, and (III) a fully degraded state defined by the PbI2 spectral signature. After 8 weeks of continuous atmospheric exposure (RH > 55%), the spin coating sample preserves the pristine state over 80% of the area, whereas the bar coating sample remained only 20%. This significant discrepancy is attributed to the superior homogeneity and thickness control achieved in the smaller 6.25 cm2 areas. Furthermore, the incorporation of additives significantly enhanced stability, with approximately 90% of the surface area maintaining adequate optical quality after 14 weeks. These findings highlight HSI as a rapid, non-destructive, and spatially resolved approach for evaluating perovskite film quality under environmental conditions, offering a practical tool for optimizing fabrication and improving device long-term.