Forum Article pubs.acs.org/IC
Interplay of Cation Ordering and Ferroelectricity in Perovskite Tin Iodides: Designing a Polar Halide Perovskite for Photovoltaic Applications Gaoyang Gou,*,†,§ Joshua Young,‡,§ Xian Liu,† and James M. Rondinelli*,⊥,∥ †
Frontier Institute of Science and Technology and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University (XJTU), Xi’ an 710049, People’s Republic of China ‡ Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States ⊥ Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, Illinois 60208-3108, United States ∥ Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States S Supporting Information *
ABSTRACT: Owing to its ideal semiconducting band gap and good carriertransport properties, the fully inorganic perovskite CsSnI3 has been proposed as a visible-light absorber for photovoltaic (PV) applications. However, compared to the organic−inorganic lead halide perovskite CH3NH3PbI3, CsSnI3 solar cells display very low energy conversion efficiency. In this work, we propose a potential route to improve the PV properties of CsSnI3. Using first-principles calculations, we examine the crystal structures and electronic properties of CsSnI3, including its structural polymorphs. Next, we purposefully order Cs and Rb cations on the A site to create the double perovskite (CsRb)Sn2I6. We find that a stable ferroelectric polarization arises from the nontrivial coupling between polar displacements and octahedral rotations of the SnI6 network. These ferroelectric double perovskites are predicted to have energy band gaps and carrier effective masses similar to those of CsSnI3. More importantly, unlike nonpolar CsSnI3, the electric polarization present in ferroelectric (CsRb)Sn2I6 can effectively separate the photoexcited carriers, leading to novel ferroelectric PV materials with potentially enhanced energy conversion efficiency.
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INTRODUCTION Halide perovskites of the form ABX3 have recently received extensive scientific attention as a new generation of highefficiency solar-cell materials. Most investigations have focused on organic−inorganic hybrid perovskite iodides, typically CH3NH3PbI3. This compound exhibits a semiconducting band gap suitable for the absorption of visible light, longrange carrier diffusion lengths, and weak exciton binding energies,1−7 allowing fabricated solar-cell devices to reach a photovoltaic (PV) energy conversion efficiency of over 15%.8 As one of its fully inorganic perovskite counterparts, CsSnI3 also exhibits a corner-connected octahedral network, a semiconducting band gap, and high carrier mobilities.9,10 However, thin-film solar cells based on CsSnI3 yield very low energy conversion efficiencies (
