Alloying chalcogenides into halide perovskites (Invited Paper)

The bandgaps of 3D lead-halide perovskites are mostly varied by changing the halide. As the electronegativity of the halide decreases, so does the bandgap, leading to gaps that are suitable for absorbing sunlight in a solar cell. Unfortunately, the stability of halide perovskites also decreases as we move to the larger and less electronegative halides, like iodides. We recently found a way to circumvent this dichotomy by mixing organochalcogenides (RS-; R = organic group) with halides in perovskites. We can now access the higher stability of bromide or chloride perovskites, while the chalcogen (S, Se) orbitals form the highest-energy filled electronic bands, affording lower bandgaps than pure-bromide or -chloride perovskites. I will present our latest findings on how mixing the halide and mixing the chalcogenide can tune the bandgap of the perovskites, in the ideal range for various photovoltaic applications. I will discuss the potential, as well as the remaining challenges, for extracting photocurrent from this new family of perovskites that may combine the properties of lead-halide and lead-chalcogenide solar absorbers.