Mechanochemical Alloying of Molecular Dopants in Expanded Analogs of Halide Perovskites

Controlling electronic doping remains a fundamental challenge for halide perovskite semiconductors. Introducing molecular dopants in the bulk of the semiconductor is a promising strategy to achieve reliable doping. Herein, we report on a solid-state alloying method that allows the incorporation of molecular dopants with low-lying lowest-unoccupied molecular orbital (LUMO) energy into the bulk of the semiconductor while enabling the fabrication of films by inkjet printing. First, we report on the synthesis and single-crystal structure of three new expanded analogs of halide perovskite (Hepm)[B2X6] (B–X = Pb–Br, Pb–I, Sn–I). The cavities in the expanded perovskite analogs are occupied by Hepm2+ cations (1-ethylpyrimidin-1,3-diium). The cations are structurally analogous to the Hepz2+ cations (1-ethylpyrazin-1,4-diium) but with higher LUMO energy (>0.5 eV). By alloying two expanded lattices via ball-milling, we obtain (Hepz)x(Hepm)1–x[Pb2Br6] and (Hepz)x(Hepm)1–x[Pb2Br6xI6–6x]. The alloyed lattices contain a mixture of molecular dopants with high (Hepm2+) and low (Hepz2+) LUMO energy, presenting optical gaps as low as 1.25(5) eV. Thus, the solid-state method allows the introduction of Hepz2+ cations in the Pb–I lattice, which remained unattained via solution methods. Finally, we also prepare pinhole-free (Hepm)[Pb2Br6] films via inkjet printing, proving that expanded perovskites containing molecular dopants are printable.