Lewis Base Passivation of Quasi-2D Ruddlesden–Popper Perovskite for Order of Magnitude Photoluminescence Enhancement and Improved Stability

Quasi-two-dimensional (2D) Ruddlesden–Popper (RP) perovskites are currently considered as the material of choice for the next-generation light-emitting diodes (LEDs) due to their superior optoelectronic properties. Despite their spectacular external quantum efficiency, the excessive surface defect states generated due to the reduced crystal size and phase impurity limit their radiative recombination efficiency. In the present work, we have shown the order of magnitude enhancement of radiative emission in butylamine (BA)-based quasi-2D perovskite (BA)2(MA)n−1PbnBr3n+1 after passivating with two different Lewis bases—a small organic molecule triphenylphosphine oxide (TPPO) and an insulating polymer polymethyl methacrylate (PMMA). The reduction in crystal grain size was observed after passivation, attributed to the complexation of the passivating molecules (PM) on the surface and nanocrystal pinning (A-NCP) phenomena. Both the steady-state and time-resolved photoluminescence study confirmed significant enhancement in fluorescence intensity and improved average lifetime (τavg. = 19.4 ns) after surface passivation. The interaction mechanism between the layered perovskite and PMs was probed with FTIR spectroscopy, XPS, and KPFM study. All these studies confirmed that the C═O group in PMMA and P═O group in TPPO deactivate the acceptor-type defects (uncoordinated Pb2+ and Br vacancies) in these RP perovskites. Furthermore, the stability of the passivated film enhanced significantly, as confirmed by contact angle measurement. Our study establishes that uncoordinated Pb2+ passivation by a Lewis base provides a viable strategy for photoluminescence (PL) lifetime, intensity, and stability enhancement in quasi-2D perovskite films.