L₂[GA_xFA_1–xPbI₃]PbI₄ (0 ≤ x ≤ 1) Ruddlesden–Popper Perovskite Nanocrystals for Solar Cells and Light-Emitting Diodes

Abstract

The main challenges to overcome for colloidal 2D Ruddlesden−Popper (RP) organo-lead iodide perovskite nanocrystals (NCs) are phase instability and low photoluminescence quantum yield (PLQY). Herein, we demonstrate colloidal synthesis of guanidinium (GA)-L 2 [GAPbI 3 ]PbI 4 , formamidinium (FA)-L 2 [FAPbI 3 ]PbI 4 , and GA and FA alloyed L 2 [GA 0.5 FA 0.5 PbI 3 ]PbI 4 NCs without using polar or high boiling point nonpolar solvents. Importantly, we show that optical properties and phase stability of L 2 [APbI 3 ]PbI 4 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 ]PbI 4 (0 ≤ x ≤ 1) NCs. Our approach produces a stable dispersion of L 2 [FAPbI 3 ]PbI 4 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 ]PbI 4 and L 2 [GA 0.5 FA 0.5 PbI 3 ]-PbI 4 NC films exhibit improved ambient stability over 10 days, which is significantly higher than L 2 [FAPbI 3 ]PbI 4 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.

Polar solvent-free room temperature synthesis of CsPbX3 (X = Br, Cl) perovskite nanocubes

“…It should be noted that, in previous works, faster charge carrier dynamics have been reported with increasing band gap energy in the perovskite nanocrystals. [45][46][47] The time resolved PL life-time decays of the CsPbBr 3 and CsPb(Cl 0.5 Br 0.5 ) 3 nanocrystals were fitted with a biexponential function and the CsPbCl 3 nanocrystals with a triexponential function (see Table 1). The average life time of the CsPbBr 3 , CsPb(Cl 0.5 Br 0.5 ) 3 , and CsPbCl 3 nanocubes are 18.98 ns, 18.97 ns, and 14.74 ns, respectively.…”

Collective Diffraction Effects in Perovskite Nanocrystal Superlattices

“…Finally, one might wonder why we first recognized multilayer diffraction in nanocubes, despite interference fringes being ubiquitous and much stronger in nanoplatelets. ,− One reason is that the XRD patterns of nanoplatelet stacks closely resemble those of layered bulk materials such as Ruddlesden–Popper perovskites and are often rationalized by this analogy. Indeed, most works on perovskite nanoplatelets acknowledge that fringes are due to their stacking, but then assign them Miller indices by analogy to the Bragg peaks of a Ruddlesden–Popper bulk crystal. ,, This diverts attention from asking why bulk-like peaks are observed in a colloidal system in the first place and why their intensity appears to be modulated over a broader profile, two key questions that could have led to the identification of a multilayer interference effect.…”

“…Here, multilayer diffraction provides substantial advantages over other techniques, as it ensures a direct and precise measurement of two parameters. Conversely, it is common to measure Λ by diffraction or TEM and then simply assume an approximate value for the nanocrystal thickness (for perovskites, generally a multiple of 0.6 nm) , or the interparticle distance (for oleylamine, generally ∼2 to 3 nm) ,,− to estimate the counterpart by difference, leading to imprecise results.…”

Metal Halide Perovskite Alloy: Fundamental, Optoelectronic Properties and Applications

“…Many alloying 2D perovskites have been reported in recent years such as (allylammonium) 2 MA nÀ1 Pb n I 3nþ1 prepared by Vasileiadou et al, [86] (4-fluorophenethylammonium) 2 (MA)Pb 2 I 7 prepared by Hu et al, [87] (methylbenzylammonium) 2 Pb 1Àx Sn x I 4 prepared by Lu et al, [88] and so on. [89][90][91] It was useful for enhancement of stability by dimension changes. For example, a large cation such as FA þ from FA-based derivative, 2-thiopheneformamidinium, has also been reported to alloy with MA þ in A-site and form a 2D protecting layer.…”