Ball milling route for stable and high-performance FAPbI3 perovskite single crystals

Abstract

Despite their immense promise for next-generation photovoltaics and photodetectors, formamidinium lead triiodide (FAPbI₃) perovskite single crystals face a critical hurdle: their inherent instability. The detrimental transition from the photoactive α-phase to the non-functional δ-phase under ambient conditions severely limits their practical application. To address this, we developed a novel hybrid strategy for FAPbI₃ single crystal growth, leveraging mechanochemical synthesis via ball milling. This process involves re-dissolving high-quality ball-milled α-FAPbI₃ powders, which are then used in the Inverse Temperature Crystallization (ITC) method. A comparative analysis with crystals grown from conventional precursor solutions (prepared by dissolving halide salts) demonstrates that our approach yields crystals with markedly improved stability and enhanced optoelectronic properties. UV-Vis spectroscopy confirmed that the ball-milled starting solution exhibits optimized coordination chemistry, particularly a higher concentration of the crucial [PbI₆]⁴⁻ species. These FAPbI₃ single crystals exhibit outstanding α-phase stability (validated by X-ray diffraction) and superior optoelectronic performance, as evidenced by photoluminescence (PL), time-resolved photoluminescence (TRPL), and space charge limited current (SCLC) measurements. Furthermore, SCLC and impedance spectroscopy (IS) data reveal a reduced trap density and suppressed recombination losses. Our findings demonstrate that ball milling is a powerful strategy for concurrently achieving outstanding stability of the desired α-FAPbI₃ phase and optimizing its optoelectronic performance, thereby paving the way for its wider integration into future optoelectronic devices.