L-2[GA(x)FA(1-x)PbI(3)]PbI4 (0 <= x <= 1) Ruddlesden-Popper Perovskite Nanocrystals for Solar Cells and Light-Emitting Diodes

The main challenges to overcome for colloidal 2D Ruddlesden-Popper (RP) organo-lead iodide perovskite nanocrystals (NCs) are phase instability and low photo-luminescence quantum yield (PLQY). Herein, we demonstrate colloidal synthesis of guanidinium (GA)-L-2[GAPbI(3)]PbI4, formamidinium (FA)-L-2[FAPbI(3)]PbI4, and GA and FA alloyed L-2[GA(0.5)FA(0.5)PbI(3)]PbI4 NCs without using polar or high boiling point nonpolar solvents. Importantly, we show that optical properties and phase stability of L-2[APbI(3)]PbI4 NCs can be affectively tuned by alloying with guanidinium and formamidinium cations. Additionally, the band gap of NCs can be rapidly engineered by bromide ion exchange in L-2[GA(x)FA(1-x)PbI(3)]PbI4 (0 = x = 1) NCs. Our approach produces a stable dispersion of L-2[FAPbI(3)]PbI4 NCs with 12.6% PLQY that is at least three times higher than the previously reported PLQY in the nanocrystals. Furthermore, L-2[GAPbI(3)]PbI4 and L-2[GA(0.5)FA(0.5)PbI(3)]PbI4 NC films exhibit improved ambient stability over 10 days, which is significantly higher than L-2[FAPbI(3)]PbI4 NC films, which transform to an undesired 1D phase within 6 days. The colloidally synthesized guanidinium- and formamidinium-based 2D RP organo-lead iodide perovskite NCs with improved stability and high PLQY demonstrated in this study may find applications in solar cells and light-emitting diodes. Therefore, large A-site cation-alloyed 2D RP perovskite NCs may provide a new way to rationalize high-performance and stable perovskite solar cells and light-emitting diodes.