Sequential thermal evaporation is an emerging technique for obtaining perovskite (PVK) photoactive materials for solar cell applications. Advantages include solvent-free processing, accurate stoichiometry control, and scalable processing. Nevertheless, the power conversion efficiency (PCE) of PVK solar cells (PSCs) fabricated by evaporation still lags behind that of solution-processed PSCs. Here, based on multi-cycle sequential thermal evaporation, we systematically investigate the effects of the post-deposition annealing temperature on the PVK properties in terms of surface morphology, opto-electronic properties, and device performance. We find that the average grain size increases to almost 1 μm and charge carrier mobilities exceed 50 cm2 V−1 s−1 when the annealing temperature is increased to 170 °C. We introduce a trace of PbCl2 to the multi-cycle sequential deposition to improve the absorber crystallinity at a lower annealing temperature of 150 °C, as evidenced by the XRD and PL analyses. The resulting PSC in a p–i–n structure yields a PCE of 18.5% with a cell area of 0.09 cm2. With the same deposition parameters, the cell area is scaled up to 0.36 cm2, achieving champion PCEs of 17.06%. This indicates the great potential of this technology for the commercialization of PSCs in the future.@en

To boost the efficiency of perovskite solar cells beyond the limit of a single-junction cell, tandem cells are employed, requiring low bandgap materials. This is realized by partially substituting lead(II) (Pb2+) with tin(II) (Sn2+) in the perovskite structure. In this work, a scalable method is presented to produce formamidinium lead tin iodide (FAPb0.5Sn0.5I3) films by sequential thermal evaporation (sTE) of PbSnI4, which is an alloy of SnI2 and PbI2, and FAI, in vacuum. Annealing at 200 °C yields a highly oriented and crystalline layer comprising grains over 1 µm on average. Photoconductance measurements reveal carrier lifetimes exceeding 2 µs and mobilities ≈100 cm2/(Vs). Structural analysis confirms that, while interdiffusion is abundant even at room temperature, the complete conversion requires high temperatures. Although the incorporation of Cs+ into the A-site of the perovskite increases the grain size, charge carrier dynamics are reduced. A comparison between the sTE films and spin-coated samples of the same composition demonstrates the superior photoconductance of the sTE films, without the need for any additives. Overall, this study showcases the potential of sTE for producing high-quality low band gap (LBG) perovskite materials.@en