AbstractQuantum dot (QD)‐based luminescent solar concentrators (LSCs) promise to revolutionize solar energy technology by replacing building materials with energy‐harvesting devices. However, QDs degrade under air, limiting the long‐term performance of QD‐LSCs. This study introduces an innovative approach to prevent QDs degradation by utilizing a photoactive polymer matrix (maleic anhydride‐grafted poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene, SEBS‐g‐MA). This strategy has been tested outdoors over a 2‐year period on five LSCs, followed by characterization of the weathered devices. The tested LSCs consist of three QD‐LSCs (CuInS2/ZnS, InP/ZnSe/ZnS, CdSe/CdS/ZnS core/shell QDs), alongside a Lumogen dye‐based LSC and a luminophore‐free LSC. The study yields several findings: 1) SEBS‐g‐MA undergoes photochemistry outdoors, 2) SEBS‐g‐MA accelerates the photodegradation of Lumogen, 3) the power conversion efficiency of CdSe‐based QD‐LSC drops by 80% due to reduction of the photoluminescence quantum yield, and 4) under illumination SEBS‐g‐MA protects CuInS2 and InP‐based QDs from degradation, ensuring a stable performance during the entire study. This work thus demonstrates for the first time that the interaction between the luminophores and the matrix is a critical determinant of the long‐term success of LSCs. Leveraging on the fact that this is the longest outdoor study to date, we propose design rules for highly efficient and stable QD‐LSCs.