  Tandem perovskite solar cells beckon as lower cost alternatives to
conventional single junction solar cells, with all-perovskite tandem
photovoltaic architectures showing power conversion efficiencies up to 26.4%.
Solution-processing approaches for the perovskite layers have enabled rapid
2optimization of perovskite solar technologies, but new deposition routes are
necessary to enable modularity and scalability, facilitating further efficiency
improvements and technology adoption. Here, we utilise a 4-source vacuum
deposition method to deposit FA$_{0.7}$ Cs$_{0.3}$Pb(I$_x$Br$_{1-x}$)$_3$
perovskite, where the bandgap is widened through fine control over the halide
content. We show how the combined use of a MeO-2PACz self-assembled monolayer
as hole transporting material and passivation of the perovskite absorber with
ethylenediammonium diiodide reduces non-radiative losses, with this
dual-interface treatment resulting in efficiencies of 17.8% in solar cells
based on vacuum deposited perovskites with bandgap of 1.76 eV. By similarly
passivating a narrow bandgap FA$_{0.75}$Cs$_{0.25}$Pb$_{0.5}$Sn$_{0.5}$I$_3$
perovskite and combining it with sub-cells of evaporated
FA$_{0.7}$Cs$_{0.3}$Pb(I$_{0.64}$Br$_{0.36}$)$_3$, we report a 2-terminal
all-perovskite tandem solar cell with champion open circuit voltage and power
conversion efficiency of 2.06 V and 24.1%, respectively. The implementation of
our dry deposition method enables high reproducibility in complex device
architectures, opening avenues for modular, scalable multi-junction devices
where the substrate choice is unrestricted.
