Synthesis and Optical Properties of Lead-Free Cesium Tin Halide Perovskite Nanocrystals

Abstract

Metal halide perovskite crystal structures have emerged as a class of optoelectronic materials, which combine the ease of solution processability with excellent optical absorption and emission qualities. Restricting the physical dimensions of the perovskite crystallites to a few nanometers can also unlock spatial confinement effects, which allow large spectral tunability and high luminescence quantum yields at low excitation densities. However, the most promising perovskite structures rely on lead as a cationic species, thereby hindering commercial application. The replacement of lead with nontoxic alternatives such as tin has been demonstrated in bulk films, but not in spatially confined nanocrystals. Here, we synthesize CsSnX3 (X = Cl, Cl0.5Br0.5, Br, Br0.5I0.5, I) perovskite nanocrystals and provide evidence of their spectral tunability through both quantum confinement effects and control of the anionic composition. We show that luminescence from Sn-based perovskite nanocrystals occurs on pico- to nanosecond time scales via two spectrally distinct radiative decay processes, which we assign to band-to-band emission and radiative recombination at shallow intrinsic defect sites.

Colloidal lead halide perovskite nanocrystals: synthesis, optical properties and applications

“…There have been some attempts to use tin instead of Pb, but this element is also not non-toxic and very unstable, as Sn (II) can easily be oxidized, transforming to the Sn(IV) state. CsSnX 3 NCs have been prepared using synthesis methods developed for their lead-containing counterparts; 67 however, the particles degrade within a few hours after preparation. Finding methods for enhancing the viability of lead-free perovskites deserves more attention in the future.…”

“…66 Driven by the wish to replace the toxic lead, Jellicoe et al synthesized CsSnX 3 perovskite NCs, with optical properties tunable both by quantum confinement and halide composition. 67 The overview of reported studies clearly suggests that reaction temperature and the choice of ligands play a vital role in determining the dimensionality and size of colloidal metal halide perovskite NCs. In general, low reaction temperatures and high ligand concentrations favor anisotropic growth, mainly producing nanoplatelets with controlled thickness and lateral sizes.…”

Metal halide perovskite light emitters

“…Pb-free perovskite emitters were reported; however, the PLQE was very low (<0.14%) and EL has not been reported yet, possibly due to the severe instability, and defects or trap states by emergence of Sn 4+ center (17)(18)(19). Some approaches, such as reducing hole-doping density and using stabilizers that reduce Sn vacancies and traps, may improve the stability of Pb-free perovskite EML and environmentally benign PeLEDs (17)(18)(19).…”

“…Especially, perovskites with high color purity, easy wavelength tuning, and efficient charge injection/ transport property have been intensively studied as promising candidates for future light emitters (8-10). Furthermore, stable and environmentally benign perovskites, which were recently reported, further raise the possibility of perovskites as future emitters in display technology (11)(12)(13)(14)(15)(16)(17)(18)(19).…”

“…Especially, perovskites with high color purity, easy wavelength tuning, and efficient charge injection/ transport property have been intensively studied as promising candidates for future light emitters (8-10). Furthermore, stable and environmentally benign perovskites, which were recently reported, further raise the possibility of perovskites as future emitters in display technology (11)(12)(13)(14)(15)(16)(17)(18)(19).However, early works on layer-type (i.e., 2D) perovskite emitters, in the 1990s, did not gain much attention (1-5). The layer-type perovskite emitters incorporating longchain organic ammoniums can generate stable excitons at low temperature, but the photoluminescence (PL) intensity dramatically decreased as temperature increased, so the perovskite light-emitting diodes (PeLEDs) exhibited electroluminescence (EL) only at low temperature (<110 K) (1-5).…”