Template-Assisted Growth of Cs<inf>x</inf>FA<inf>1-x</inf>PbI<inf>3</inf> with Pulsed Laser Deposition for Single Junction Perovskite Solar Cells

Cesium-formamidinium lead iodide (CsxFA1-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 CsxFA1-xPbI3 perovskite films using pulsed laser deposition (PLD) from a single-source target of mixed precursors. Implementing a lead iodide (PbI2) + CsxFA1-xPbI3 tailored template, phase-pure CsxFA1-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 Cs0.2FA0.8PbI3 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-CsxFA1-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.