Combining perovskites with silicon is a particularly attractive option for producing cheap, high efficiency and high voltage solar cells. Perovskite-on-silicon tandem solar cells can potentially achieve over 30% tandem efficiency, which greatly surpasses the current record of 25.6% for the single silicon cell.
We demonstrate a 4-terminal tandem configuration in which the efficiency is as high as 26%, which is the highest efficiency that has been achieved with a potentially low cost process . We also demonstrate a two-terminal monolithic tandem device with a perovskite top subcell and a high-temperature tolerant homojunction c-Si bottom subcell, with an efficiency of over 22% . Several developments have been instrumental in achieving these high efficiencies. The first is development of a combined grid/transparent conducting oxide back contact for the top subcell of 4-terminal tandems, which allows over 80% of long wavelength light to pass through to the silicon solar cell underneath . Incorporation of rubidium in a multi-cation perovskite improves both efficiency and stability . Doping the compact TiO2 layer with indium also improves conductivity and band alignment . Finally we have also found that a combination of PMMA and PCBM can provide effective interface passivation for perovskite solar cells . These results show the clear potential of perovskites in practical high efficiency tandem devices.
 The Duong et al, Rubidium Multication Perovskite with Optimized Bandgap for Perovskite-Silicon Tandem with over 26% Efficiency, Advanced Energy Materials, 7, 14, 1700228 (2017).
 Yiliang Wu et al., Monolithic perovskite/silicon-homojunction tandem solar cell with over 22% efficiency, Energy and Environmental Science, in press (2017).
 The Duong et al, Semi-transparent perovskite solar cell with sputtered front and rear electrodes for a four-terminal tandem, IEEE Journal of Photovoltaics 6 (3), 679-687 (2016).
 The Duong et al, Structural engineering using rubidium iodide as a dopant under excess lead iodide conditions for high efficiency and stable perovskites, Nano Energy, 30, 330 (2016).
 Jun Peng et al, Interface engineering of high performance perovskite solar cells and perovskite-silicon tandems, Advanced Energy Materials, 10.1002/aenm.201601768 (2016).
 Jun Peng et al, Interface passivation using ultrathin polymer-fullerene films for high-efficiency perovskite solar cells with negligible hysteresis, Energy and Environmental Science, DOI: 10.1039/C7EE01096F (2017).