A green solvent system for precursor phase-engineered sequential deposition of stable formamidinium lead triiodide for perovskite solar cells
Benjamin Gallant a, Philippe Holzhey b, Joel Smith b, Dominik Kubicki a, Henry Snaith b
a School of Chemistry, University of Birmingham, Edgbaston B15 2TT, UK
b Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV25)
Roma, Italy, 2025 May 12th - 14th
Organizers: Filippo De Angelis, Francesca Brunetti and Claudia Barolo
Poster, Benjamin Gallant, 212
Publication date: 17th February 2025

Perovskite solar cells (PSCs) offer an efficient, inexpensive alternative to current photovoltaic technologies, with the potential for manufacture via high-throughput coating methods. However, challenges for commercial-scale solution-processing of metal-halide perovskites include the use of harmful solvents, the expense of maintaining controlled atmospheric conditions, and the inherent instabilities of PSCs under operation. Here, we address these challenges by introducing a high volatility, low toxicity, biorenewable solvent system to fabricate a range of 2D perovskites, which we use as highly effective precursor phases for subsequent transformation to α-formamidinium lead triiodide (α-FAPbI3), fully processed under ambient conditions. We probe this transformation, and the resulting α-FAPbI3 thin film materials, using a combination of in-situ grazing incidence wide-angle X-ray scattering (GIWAXS) with synchrotron radiation, nuclear magnetic and quadrupole resonance (NMR/NQR) spectroscopy, and electron microscopy techniques, and present a complete mechanistic description of the 2D-to-3D transformation process. PSCs utilising the α-FAPbI3 reproducibly show remarkable stability under illumination and elevated temperature (ISOS-L-2) and “damp heat” (ISOS-D-3) stressing, surpassing other state-of-the-art perovskite compositions. We determine that this enhancement is a consequence of the 2D precursor phase crystallisation route, which simultaneously avoids retention of residual low-volatility solvents (such as DMF and DMSO) and reduces the rate of degradation of FA+ in the material. These findings highlight both the critical role of the initial crystallisation 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.

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