Deciphering the Role of Water in Promoting the Optoelectronic Performance of Surface-Engineered Lead Halide Perovskite Nanocrystals

Abstract

Lead halide perovskites are promising candidates for high-performance light-emitting diodes (LEDs); however, their applicability is limited by their structural instability toward moisture. Although a deliberate addition of water to the precursor solution has recently been shown to improve the crystallinity and optical properties of perovskites, the corresponding thin films still do not exhibit a near-unity quantum yield. Herein, we report that the direct addition of a minute amount of water to post-treated formamidinium lead bromide (FAPbBr3) nanocrystals (NCs) substantially enhances the stability while achieving a 95% photoluminescence quantum yield in a NC thin film. We unveil the mechanism of how moisture assists in the formation of an additional NH4Br component. Alongside, we demonstrate the crucial role of moisture in assisting localized etching of the perovskite crystal, facilitating the partial incorporation of NH4 +, which is key for improved performance under ambient conditions. Finally, as a proof-of-concept, the application of post-treated and water-treated perovskites is tested in LEDs, with the latter exhibiting a superior performance, offering opportunities toward commercial application in moisture-stable optoelectronics.

Achieving High Moisture Tolerance in Pseudohalide Perovskite Nanocrystals for Light-Emitting Diode Application

“…Interestingly, PT1 also exhibited a 5-fold higher EQE (1.5% at 523 nm) compared to PT0 (0.3% at 540 nm), which is attributed to the defect healing ability of the salts after post-treatment. Notably, the attained value of EQE for PT1 NCs is 6 times higher than our previous report on FAPbBr 3 NCs (both proof-of-concept LEDs) . These findings demonstrate the positive impact of the addition of KSCN to the FAPbBr 3 structure and subsequent post-treatment on the optoelectronic properties of perovskites.…”

“…Notably, the attained value of EQE for PT1 NCs is 6 times higher than our previous report on FAPbBr 3 NCs (both proof-of-concept LEDs). 15 These findings demonstrate the positive impact of the addition of KSCN to the FAPbBr 3 structure and subsequent post-treatment on the optoelectronic properties of perovskites.…”

“…Subsequently, upon post-treating the NCs, an intense tertiary phase belonging to NH 4 Br is also observed (marked with #), owing to the base-catalyzed hydrolysis of FABr. 15 Notably, all of these additional phases did not hamper any photophysical properties but rather enhanced the structural stability, consequently boosting the optoelectronic performance. Moreover, the XRD pattern further shifts to a higher angle, indicating lattice contraction, which is consistent with the STEM results, which also showed a reduction in the lattice parameter (6.174 Å, Figure S2c) compared to PT0 (6.201 Å).…”

“…Notably, the PL decay profile changes from triexponential to biexponential upon aging, which is an indication of reduction of the exciton recombination processes (assigned as τ 3 ). 15 This is potentially attributed to the reduction in crystal symmetry (Figure S9), which does not necessarily modify the concentration of surface defects but impacts the exciton recombination pathway.…”

“…The authors acknowledge financial support from the Research Foundation�Flanders (FWO Grant Numbers S002019N, 1514220N, G.0B39. 15…”