Pseudohalide (SCN^–)‑Doped MAPbI₃ Perovskites: A Few Surprises

Abstract

Pseudohalide thiocyanate anion (SCN^–) has been used as a dopant in a methylammonium lead tri-iodide (MAPbI₃) framework, aiming for its use as an absorber layer for photovoltaic applications. The substitution of SCN^– pseudohalide anion, as verified using Fourier transform infrared (FT-IR) spectroscopy, results in a comprehensive effect on the optical properties of the original material. Photoluminescence measurements at room temperature reveal a significant enhancement in the emission quantum yield of MAPbI_3–<i>x</i>(SCN)_<i>x</i> as compared to MAPbI₃, suggestive of suppression of nonradiative channels. This increased intensity is attributed to a highly edge specific emission from MAPbI_3–<i>x</i>(SCN)_<i>x</i> microcrystals as revealed by photoluminescence microscopy. Fluoresence lifetime imaging measurements further established contrasting carrier recombination dynamics for grain boundaries and the bulk of the doped material. Spatially resolved emission spectroscopy on individual microcrystals of MAPbI_3–<i>x</i>(SCN)_<i>x</i> reveals that the optical bandgap and density of states at various (local) nanodomains are also nonuniform. Surprisingly, several (local) emissive regions within MAPbI_3–<i>x</i>(SCN)_<i>x</i> microcrystals are found to be optically unstable under photoirradiation, and display unambiguous temporal intermittency in emission (blinking), which is extremely unusual and intriguing. We find diverse blinking behaviors for the undoped MAPbI₃ crystals as well, which leads us to speculate that blinking may be a common phenomenon for most hybrid perovskite materials