The high-performance light-management slabs made of low-cost, highly emissive, and ultra-stable nanocrystal (NC)-polymer composites are desirable for application in large-area luminescent solar concentrators (LSCs). However, although the reported photoluminescence (PL) quantum yield (QY) of NCs in solution is up to 90%, PL QY of NCs in a polymer matrix is usually low, which limits the performance of LSCs. Herein, we demonstrated a new strategy for the synthesis of formamidinium lead bromide (FAPbBr₃) NCs via room-temperature solvent-induced reprecipitation using dicarboxylic acids as ligands and the preparation of NC-polymer composite slabs for LSCs. Due to the strong binding of dicarboxylic acids, the as-synthesized decanedioic acid (DA)-capped FAPbBr₃ NCs displayed high PL QY (90 ± 5%), increased chemical yield, and improved stability as compared to monocarboxylic oleic acid (OA)-capped NCs (PL QY of 80 ± 5%) synthesized in the same conditions. Furthermore, in the presence of toluene as the solvent, these DA-capped NCs exhibited good compatibility with polystyrene (PS); thus, the NCs-PS slurry exhibited appropriate viscosity. Therefore, it was convenient to deposit the slurry onto commercially available polymethyl methacrylate (PMMA) slabs with a standard doctor blade. The optimized NCs-PS-PMMA slabs with PL QY of 92 ± 5% were sustained for over 1000 hours under high-temperature (60 °C) and high-humidity (relative humidity, RH = 90%) environments. The results show that the perovskite NC-based slabs developed in this study have the advantages of low cost, high emissivity, and good stability and may contribute to the field of LSCs.