Perovskite solar cells (PSCs) use perovskites with an APbX3 structure, where A is a monovalent cation and X is a halide such as Cl, Br, and/or I. Currently, the cations for high-efficiency PSCs are Rb, Cs, methylammonium (MA), and/or formamidinium (FA). Molecules larger than FA, such as ethylammonium (EA), guanidinium (GA), and imidazolium (IA), are usually incompatible with photoactive “black”-phase perovskites. Here, novel molecular descriptors for larger molecular cations are introduced using a “globularity factor”, i.e., the discrepancy of the molecular shape and an ideal sphere. These cationic radii differ significantly from previous reports, showing that especially ethylammonium (EA) is only slightly larger than FA. This makes EA a suitable candidate for multication 3D perovskites that have potential for unexpected and beneficial properties (suppressing halide segregation, stability). This approach is tested experimentally showing that surprisingly large quantities of EA get incorporated, in contrast to most previous reports where only small quantities of larger molecular cations can be tolerated as “additives”. MA/EA perovskites are characterized experimentally with a band gap ranging from 1.59 to 2.78 eV, demonstrating some of the most blue-shifted PSCs reported to date. Furthermore, one of the compositions, MA0.5EA0.5PbBr3, shows an open circuit voltage of 1.58 V, which is the highest to date with a conventional PSC architecture.
Bibliographical noteFunding Information:
S.G. gratefully acknowledges the Ministry of Science, Research and Technology of Iran and Iranian’s National Elites Foundation and Iranian Nano Technology Initiative Council for financial support. M.S. acknowledges support from the cofunded Marie Skłodowska Curie fellowship, H2020 Grant Agreement No. 665667.
- light-emitting devices
- perovskite solar cells
- quasi-3D cations
- wide band-gap semiconductors