Current understanding of the effects of various A-site cations on the photophysical properties of halide perovskites (APbI 3 ) is limited by the compositional tunability. Here we report the synthesis and characterization of colloidal nanoplates of a series of 2D Ruddlesden–Popper (RP) perovskites (HA) 2 (A)Pb 2 I 7 (HA = n -hexylammonium) with seven small and large A-site cations to reveal the size effects of such A cations. Absorbance and photoluminescence (PL) measurements show a clear parabolic trend of the optical band gap versus the A cation size, with methylammonium and formamidinium near the bottom. This band gap shifting is attributed to the changing chemical pressure inside the A-site cavity templating the Pb–I framework. PL quantum yield and time-resolved PL measurements show the effect of A cation size on the PL efficiencies and carrier lifetimes. This fundamental investigation can inform the choices of A-site cations that can be incorporated into halide perovskite materials for optoelectronic applications.
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Hautzinger et al. (2020) studied this question.
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