Researchers from the University of Oxford, University of Manchester, University of Sheffield and Helmholtz-Zentrum Berlin (HZB) have developed a high volatility, low toxicity, biorenewable solvent system to fabricate a range of 2D perovskites, which can be used as effective precursor phases for subsequent transformation to α-formamidinium lead triiodide (α-FAPbI3), fully processed under ambient conditions.
This solvent system is meant to address challenges involved with producing perovskite solar cells (PSCs) via high-throughput coating methods, such as the use of harmful solvents, the expense of maintaining controlled atmospheric conditions, and the inherent instabilities of PSCs under operation.
The precursor ink utilizes a highly volatile, low toxicity solvent mixture, enabling the replacement of conventional precursor phases with a solid-state 2D perovskite material. By exchanging the organic cations in the 2D precursor phase with FA+, the team enabled the subsequent crystallization of α-FAPbI3 perovskite. The scientists not only found that their α-FAPbI3 performs effectively in PSCs, but that 2D-precursor phase growth produces α-FAPbI3 with substantially improved ambient, thermal and photostability in comparison to other perovskite composition or processing routes.
The team was able to fabricate neat FAPbI3 thin films that were stable for >3000 hours under harsh heat, light and moisture conditions, and achieve a promising champion lifetime to 80% of initial performance (t80) of 800 hours and no degradation (t100) for more than 1930 hours under ISOS-L-2 (85 °C, 1-sun equivalent) and ISOS-D-3 (85 °C, 85% relative humidity), respectively, when integrated into PSCs. This work enabled the team to distinguish how different processing variables impact perovskite stability and demonstrate why conventional solution processing routes are not only problematic for toxicity but are fundamentally linked to halide perovskite instability.
These findings highlight both the critical role of the initial crystallization process in determining the operational stability of perovskite materials, and that neat FA+-based perovskites can be competitively stable despite the inherent metastability of the α-phase.
