Porphyrin Functionalization of CsPbBrI₂/SiO₂ Core–Shell Nanocrystals Enhances the Stability and Efficiency in Electroluminescent Devices

Abstract

Surface ligand exchange on all‐inorganic perovskite nanocrystals of composition CsPbBrI2 reveals improved optoelectronic properties due to strong interactions of the nanocrystal with mono‐functionalized porphyrin derivatives. The interaction is verified experimentally with an array of spectroscopic measurements as well as computationally by exploiting density functional theory calculations. The enhanced current efficiency is attributed to a lowering of the charging energy by a factor of 2–3, which is determined by combining electronic and optical measurements on a selection of ligands. The coupled organic–inorganic nanostructures are successfully deployed in a light‐emitting device with higher current efficacy and improved charge carrier balance, magnifying the efficiency almost fivefold compared to the native ligand.

Quantum Efficiency Enhancement of Lead-Halide Perovskite Nanocrystal LEDs by Organic Lithium Salt Treatment

“…Together with the changes in the PLQY of LiTFSI-treated CsPbBr 3 NC films, we also observed a slight red shift of their PL emission spectra (Figure S1), which is indicative of ligand exchange by the addition of LiTFSI to the NC solutions prior to spin-coating. Similar observations were recently reported on red-emitting LHP NC and were assigned to the highly dynamic/labile binding situation of oleic acid and oleylamine on the perovskite NC surface. , Therefore, both the enhanced PLQY and the spectral PL red shift indicate that the new ligand must be in spatial proximity to the NC surface, which is only possible if the native ligand (oleic acid/oleylamine) is replaced.…”

Mitigating the photodegradation of all-inorganic mixed-halide perovskite nanocrystals by ligand exchange

“…31 During XPS, the NCs are subject to substantial charging and, while not all considerations for the reduction of Cd in CdSe may be transferable to Pb in CsPbBrI 2 , we argue that the general rational outlined by du Fossé et al is of central importance also in the present case: mZnTPP invokes a 0.5 eV increase in work function (Fig. 5(a)) and provides better dielectric screening (a higher permittivity) 26 compared to the native ligand. As du Fossé et al have shown, a reduced work function affects primarily the overall crystal and only to a lesser extent a localized state, such as Pb 0 .…”

“…31 During XPS, the NCs are subject to substantial charging and, while not all considerations for the reduction of Cd in CdSe may be transferable to Pb in CsPbBrI 2 , we argue that the general rational outlined by du Fosse ´et al is of central importance also in the present case: mZnTPP invokes a 0.5 eV increase in work function (Fig. 5(a)) and provides better dielectric screening (a higher permittivity) 26 Thus, a promising strategy to further enhance the stability of perovskite NCs is the search for ligands that induce even larger work functions. We note that both degradation pathways -with and without mZnTPP -are preceded by the same core level energy shifts of Pb and Cs (Fig.…”

“…Lastly, the conductivities of the native as well as the mZnTPP exchanged sample are known. 26 The electric resistance in the porphyrin-containing sample is lower and should result in a smaller shift. However, we find the same shifts independent of the ligand shell and can thus assume that the shift does not originate from charging.…”

“…Motivated by the previous finding that ligand exchange with mZnTPP can enhance the stability of red perovskites in light emitting devices, 26 we studied the effect of this ligand on the decomposition of the red perovskites under X-ray illumination. (Note: the loss of structural integrity of the blue perovskites due to chlorine evaporation did not allow for an analogous analysis.)…”