Defect-Induced Band-Edge Reconstruction of a Bismuth-Halide Double Perovskite for Visible-Light Absorption
Adam H. Slavney (Stanford University)
Linn Leppert (Lawrence Berkeley National Laboratory, University of California)
Davide Bartesaghi (Material Innovation Institute (M2i), TU Delft - ChemE/Opto-electronic Materials)
Aryeh Gold-Parker (Stanford University, Stanford Synchrotron Laboratory)
Michael F. Toney (Stanford Synchrotron Laboratory)
Tom J. Savenije (TU Delft - ChemE/Opto-electronic Materials)
Jeffrey B. Neaton (Lawrence Berkeley National Laboratory, University of California)
Hemamala I. Karunadasa (Stanford University)
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Abstract
Halide double perovskites have recently been developed as less toxic analogs of the lead perovskite solar-cell absorbers APbX3 (A = monovalent cation; X = Br or I). However, all known halide double perovskites have large bandgaps that afford weak visible-light absorption. The first halide double perovskite evaluated as an absorber, Cs2AgBiBr6 (1), has a bandgap of 1.95 eV. Here, we show that dilute alloying decreases 1's bandgap by ca. 0.5 eV. Importantly, time-resolved photoconductivity measurements reveal long-lived carriers with microsecond lifetimes in the alloyed material, which is very promising for photovoltaic applications. The alloyed perovskite described herein is the first double perovskite to show comparable bandgap energy and carrier lifetime to those of (CH3NH3)PbI3. By describing how energy- and symmetry-matched impurity orbitals, at low concentrations, dramatically alter 1's band edges, we open a potential pathway for the large and diverse family of halide double perovskites to compete with APbX3 absorbers.