Lead-halide perovskite APbX₃ (A=Cs or organic cation; X=Cl, Br, I) nanocrystals (NCs) are subject of intense research due to their exceptional properties as both classical¹ and quantum light sources.^2-4 Many challenges often faced with this material class concern the long-term optical stability, a serious intrinsic issue connected with the labile and polar crystal structure of APbX₃ compounds. When conducting spectroscopy at a single particle level, due to the highly enhanced contaminants (e.g., water molecules, oxygen) over NC ratio, deterioration of NC optical properties occurs within tens of seconds, with typically used excitation power densities (1-100 W/cm²), and in ambient conditions.

Here,⁵ we demonstrate that choosing a suitable polymer matrix is of paramount importance for obtaining stable spectra from a single NC and for suppressing the dynamic photoluminescence (PL) blueshift. In particular, polystyrene (PS), the most hydrophobic amongst four tested polymers, leads to the best optical stability, one-to-two orders of magnitude higher than that obtained with poly-(methyl methacrylate) (PMMA), a common polymeric encapsulant containing polar ester groups. Molecular mechanics simulations based on a force-field approximation corroborate the hypothesis that PS affords for a denser molecular packing at the NC surface. These findings underscore the often-neglected role of the sample preparation methodologies for the assessment of the optical properties of perovskite NCs at a single-particle level and guide the further design of robust single photon sources. 

[1] Akkerman et al. Nature Materials, 2018, 17, 394–405.
[2] Becker et al. Nature, 2018, 553, 189–193.
[3] Rainò et al. Nature, 2018, 563, 671–675.
[4] Utzat et al. Science, 2019, 363, 1068–1072.
[5] Rainò et al. submitted 2019