PT  - JOURNAL ARTICLE
AU  - Tong, Jinhui
AU  - Song, Zhaoning
AU  - Kim, Dong Hoe
AU  - Chen, Xihan
AU  - Chen, Cong
AU  - Palmstrom, Axel F.
AU  - Ndione, Paul F.
AU  - Reese, Matthew O.
AU  - Dunfield, Sean P.
AU  - Reid, Obadiah G.
AU  - Liu, Jun
AU  - Zhang, Fei
AU  - Harvey, Steven P.
AU  - Li, Zhen
AU  - Christensen, Steven T.
AU  - Teeter, Glenn
AU  - Zhao, Dewei
AU  - Al-Jassim, Mowafak M.
AU  - van Hest, Maikel F. A. M.
AU  - Beard, Matthew C.
AU  - Shaheen, Sean E.
AU  - Berry, Joseph J.
AU  - Yan, Yanfa
AU  - Zhu, Kai
TI  - Carrier lifetimes of >1 μs in Sn-Pb perovskites enable efficient all-perovskite tandem solar cells
AID  - 10.1126/science.aav7911
DP  - 2019 May 03
TA  - Science
PG  - 475--479
VI  - 364
IP  - 6439
4099  - http://science.sciencemag.org/content/364/6439/475.short
4100  - http://science.sciencemag.org/content/364/6439/475.full
SO  - Science2019 May 03; 364
AB  - Organic-inorganic perovskite films can boost the output of conventional silicon solar cells in tandem geometries by utilizing more of the light at the blue end of the solar spectrum. Tandem cells that use only perovskite films have been less successful because of the lack of a suitable material with a low bandgap that can replace silicon. Tong et al. report that a mixed tin-lead organic-inorganic material containing a small fraction of guanidinium thiocyanate has a low bandgap, long charge-carrier lifetime, and efficiencies around 25%.Science, this issue p. 475All-perovskite–based polycrystalline thin-film tandem solar cells have the potential to deliver efficiencies of >30%. However, the performance of all-perovskite–based tandem devices has been limited by the lack of high-efficiency, low–band gap tin-lead (Sn-Pb) mixed-perovskite solar cells (PSCs). We found that the addition of guanidinium thiocyanate (GuaSCN) resulted in marked improvements in the structural and optoelectronic properties of Sn-Pb mixed, low–band gap (~1.25 electron volt) perovskite films. The films have defect densities that are lower by a factor of 10, leading to carrier lifetimes of greater than 1 microsecond and diffusion lengths of 2.5 micrometers. These improved properties enable our demonstration of >20% efficient low–band gap PSCs. When combined with wider–band gap PSCs, we achieve 25% efficient four-terminal and 23.1% efficient two-terminal all-perovskite–based polycrystalline thin-film tandem solar cells.