Template-Assisted Growth of Cs_xFA_1-xPbI₃ with Pulsed Laser Deposition for Single Junction Perovskite Solar Cells

Cesium-formamidinium lead iodide (Cs_xFA_1-xPbI₃) perovskites are a promising methylammonium-free alternative for efficient single-junction solar cells. However, they have not been fully explored by vapor-phase deposition techniques. Herein, a template-assisted approach is demonstrated for the growth of Cs_xFA_1-xPbI₃ perovskite films using pulsed laser deposition (PLD) from a single-source target of mixed precursors. Implementing a lead iodide (PbI₂) + Cs_xFA_1-xPbI₃ tailored template, phase-pure Cs_xFA_1-xPbI₃ films with uniform coverage on both planar and textured substrates are achieved. Compositional analysis via X-ray fluorescence confirms near-stoichiometric transfer of the inorganic cations (Cs/Pb), with identical Cs_0.2FA_0.8PbI₃ composition and a bandgap of 1.58 eV achieved in templated and non-templated films. However, the presence of the template proves essential for attaining phase-pure films in the photoactive cubic (α-) phase. Proof-of-concept solar cells fabricated with templated-PLD α-Cs_xFA_1-xPbI₃ achieve an efficiency exceeding 12.9% on 0.1 cm² area devices without the employment of passivation approaches. Additionally, increasing deposition rates does not alter the phase, morphology, or optoelectronic properties of the templated films on textured substrates, indicating the robustness of this methodology. The compositional control of PLD for Cs-FA-based perovskites is showcased, and template-assisted growth is demonstrated as a reliable pathway to high-quality reproducible perovskite films.