Chloride-improved crystallization in sequentially vacuum-deposited perovskites for p–i–n perovskite solar cells†

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.