Monolithic Wide Band Gap Perovskite/Perovskite Tandem Solar Cells with Organic Recombination Layers

We demonstrate a monolithic tandem solar cell by sequentially depositing a higher-bandgap (2.3 eV) CH3NH3PbBr3 sub-cell and a lower-bandgap (1.55 eV) CH3NH3PbI3 sub-cell bandgap perovskite cells, in conjugation with a solution-processed organic charge carrier recombination layer, which serves to protect the underlying sub-cell and allows for voltage addition of the two sub-cells. Owing to the low-loss series connection, we achieve a large open-circuit voltage of 1.96 V. Through optical and electronic modelling, 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 optimised 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 in this study could be an advantage for triple junction cells on top of silicon. Our findings indicate that wide band gap all-perovskite tandems could be a feasible device structure for higher efficiency perovskite thin-film solar cells