Tin halide perovskites (THP) are one of the most promising and less toxic alternatives to lead-based perovskite solar cells. These materials have gained increasing interest in recent decades due to their exceptional optoelectronic properties and related tunability, straightforward processing and high efficiencies, approachable to silicon solar cell’s ones. Despite the outstanding properties of THPs, one of the main disadvantages of this class of materials is the high concentration of defects present in the bulk, due to Sn (II) instability and intrinsic tendency to oxidise over time. The consequent self p-doping of the perovskite leads to increased free-charge recombination rate and reduced efficiency of solar cells. Engineering the surface passivation of tin perovskites is one of the key strategies to address both stability and performance enhancement of solar cells, for example by using additives, such as tin halides or hydrazine, which is a potent reducing agent able to compensate for tin vacancies.

Among the various strategies explored, mainly solvent-based, we investigated for the first time an innovative use of plasma as a solvent-free, reproducible and scalable approach, 1,2 to gently modify the perovskite surface and reduce surface defects. A preliminary study focused on nitrogen-based plasma treatment, applied to a DMSO-free FASnI3 perovskite surface 3. The mild nature of the plasma process enabled subtle surface modifications, effectively suppressing the natural tendency of tin (II) to oxidize, as confirmed by the XPS analysis performed on aged films. Subsequently, we extended this approach to a FASnI2.7Br0.3 perovskite, employing a plasma generated from a mixture of N2 and H2 gases. Owing to the reducing character of hydrogen-based plasma, we observed a notable enhancement in device performance, accompanied by increased photoluminescence and reduced non-radiative recombination. The reactive hydrogen species generated within the plasma interact with the perovskite surface, mitigating carrier losses associated with self-doping, thereby contributing to improved device efficiency. 4

These studies establish the basis for a novel application of plasma technology to enhance tin-based perovskite solar cells, offering an approach that is not only effective but also readily scalable for industrial implementation.

Armenise, V., Covella, S., Fracassi, F., Colella, S. & Listorti, A. Plasma‐Based Technologies for Halide Perovskite Photovoltaics. Solar RRL (2024) doi:10.1002/solr.202400178.

Perrotta, A. et al. Plasma-Driven Atomic-Scale Tuning of Metal Halide Perovskite Surfaces: Rationale and Photovoltaic Application. Solar RRL (2023) doi:10.1002/solr.202300345.

Covella, S. et al. Plasma-Based Modification of Tin Halide Perovskite Interfaces for Photovoltaic Applications. ACS Appl Mater Interfaces (2024) doi:10.1021/acsami.4c09637.

Covella, S. et al. manuscript in preparation.