Efficient all-perovskite tandem solar cells by dual-interface optimisation of vacuum-deposited wide-bandgap perovskite

Abstract

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.