LAUSR

We demonstrate a monolithic tandem solar cell by sequentially depositing a higher-bandgap (2.3 eV) CH3NH3PbBr3 subcell and a lower-bandgap (1.55 eV) CH3NH3PbI3 subcell bandgap perovskite cells, in conjugation with a solution-processed organic charge carrier recombination layer, which serves to protect the underlying subcell and allows for voltage addition of the two subcells. Owing to the low-loss series connection, we achieve a large open-circuit voltage of 1.96 V. Through optical and electronic modeling, we estimate the feasible efficiency of this device architecture to be 25.9%, achievable with integrating a best-in-class CH3NH3PbI3 sub cell and a 2.05 eV wide bandgap perovskite cell with an optimized optical structure. Compared to previous reported all-perovskite tandem cells, we solely employ Pb-based perovskites, which although have wider band gap than Sn based perovskites, are not at risk of instability due to the unstable charge state of the Sn2+ ion. Additionally, the bandgap combination we use i...