The crystallinity properties of perovskite influence their optoelectrical performance in solar cell applications. We optimized the grain shape and crystallinity of perovskite film by annealing treatment from 130 to 170 °C under high humidity (relative humidity of 70%). We found that the grain size, grain interface, and grain morphology of the perovskite are optimized when the sample was annealed at 150 °C for 1 h in the air. At this condition, the perovskite film is composed of 250 nm crystalline shape grain and compact inter-grain structure with an invincible grain interface. Perovskite solar cells device analysis indicated that the device fabricated using the samples annealed at 150 °C produced the highest power conversion efficiency, namely 17.77%. The open circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF) of the device are as high as 1.05 V, 22.27 mA/cm2, and 0.76, respectively. Optoelectrical dynamic analysis using transient photoluminescence and electrochemical impedance spectroscopies reveals that (i) carrier lifetime in the champion device can be up to 25 ns, which is almost double the carrier lifetime of the sample annealed at 130 °C. (ii) The interfacial charge transfer resistance is low in the champion device, i.e., ~20 Ω, which has a crystalline grain morphology, enabling active photocurrent extraction. Perovskite's behavior under annealing treatment in high humidity conditions can be a guide for the industrialization of perovskite solar cells.
The ambient processing of perovskite solar cells (PSCs) is crucial for scalable industrialization; however, moisture-induced degradation and non-uniform crystallization remain significant hurdles. In this work, we demonstrate a facile, ambient-processable two-step intercalation strategy that premixes cesium iodide (CsI) directly into the PbI2 precursor to regulate the crystallization and carrier dynamics of methylammonium lead iodide (MAPbI3) PSCs. By bypassing conventional solution-processed solubility limits, this pre-intercalation approach ensures a highly uniform Cs+ distribution. Mechanistically, this kinetically promotes Ostwald ripening during crystal growth and thermodynamically relieves native lattice microstrain. Consequently, the optimal CsI concentration (2 mg mL-1) significantly enlarged the perovskite grain size (from 161 nm to 255 nm), reduced dislocation density, and suppressed deep-level trap states. These structural refinements effectively mitigated trap-assisted recombination and improved charge extraction. The optimal ambient-processed device achieved a champion power conversion efficiency (PCE) of 23.17% (average 20.57 ± 1.28%) with minimized hysteresis. Furthermore, applying this CsI-intercalated architecture in a strictly controlled environment (glovebox) validated its fundamental optoelectronic potential, yielding a true PCE of 23.78% with an excellent fill factor of 80.9%. Finally, the unencapsulated devices demonstrated remarkable durability, retaining 97.7% of their initial efficiency under continuous operational illumination and 82% after 30 days of ambient storage. These findings establish controlled CsI precursor intercalation as a scalable and mechanistically sound pathway for highly efficient and stable perovskite photovoltaics.