Multi-Scalable Grain Growth via Phenyl‑C₆₀-Butyric Acid Methyl Ester Molecular Aggregation in Perovskite Solar Cells

The light-harvesting properties of perovskite solar cells (PeSCs) are determined by a handful of properties, including the grain size of the perovskite crystallites. Here, we report a successful strategy for controlling the grain sizes of MAPbI₃ perovskite films via inducing solubility-dependent aggregation of the phenyl-C₆₀-butyric acid methyl ester (PCBM) molecules in the solution. The solubility of PCBM in toluene (Tol) was modulated by varying the solution temperature from 75 to 25 °C, which provides a mean for tuning the grain size over an order of magnitude from 0.8–1.4 to 18.1–23.2 μm. Using this tunability of grain size, we demonstrate the correlation between the grain size of perovskites and the electrical property via transient charge dynamics and impedance spectroscopy in solar cells. Devices prepared by this method exhibit much shorter extraction times (1.46–0.88 μs) and improved recombination resistances (20.7–93.3 kΩ), compared to the control devices. Optimization of the PCBM solution temperature results in PeSCs with a higher power conversion efficiency of 15.95% and current density (J_sc) of 22.93 mA cm^–2, compared to those using pure Tol treatment (11.42% and 16.51 mA cm^–2). Our approach therefore provides a facile and promising method for improving the performance and stability of PeSCs by controlling the grain size of perovskites.