Deciphering the roles of ammonium doping for lead-free (NH4)xCs3−xCu2I5 perovskites to regulate the photoelectronic properties

Inorganic ammonium (NH4+) is the simplest amine cation with perfect symmetry, the smallest radius and many H atoms, allowing itself to be used as a potential dopant in achieving high-quality perovskite materials. As a composition-modulation strategy, NH4+-doped (NH4)xCs3-xCu2I5 (0 < x < 1.5) lead-free perovskites were successfully synthesized via the eco-friendly ball milling method in this work. As the ammonium content increases, the lattice constants of (NH4)xCs3-xCu2I5 shrink and the grain sizes increase. The doping of NH4+ effectively passivates the lattice defects, suppresses the non-radiative recombination and tunes the energy band structure, resulting in better fluorescence properties. UV-pumped deep-blue LEDs based on (NH4)xCs3-xCu2I5 phosphors were fabricated, which showed improved performance and tunable emission. These results demonstrate the potential of the NH4+-doping strategy for improving the performance of lead-free perovskite optoelectronics.