Incorporation of insulating polymers or molecules into organic semiconductor films, creating so-called diluted organic semiconductors, has been successfully used both in organic field-effect transistors and organic light-emitting diodes to reduce sensitivity to charge traps. However, application of this strategy in organic photovoltaics is challenging due to the complex requirements on the light-absorbing blend layer. Herein, diluted donor-acceptor-insulator ternary organic solar cells are developed to improve mobility and decrease radiative and nonradiative recombination in the active layer. In addition, both thermal and environmental stability of the diluted ternary solar cells are enhanced. Finally, the diluted semiconductor approach enables large-area solar cells to be fabricated where the loss in power density upon cell area upscaling is five times lower than for the equivalent binary cells.