This work demonstrates a novel photovoltaic application in which graphdiyne (GD) can be employed as a host material in a perovskite active layer for the first time. In the device fabrication, the best molar ratio for active materials is verified as PbI2/MAI/GD being 1:1:0.25, yielding a peak power-conversion efficiency of 21.01%. We find that graphdiyne, as the host material, exerts significant influence on the crystallization, film morphology, and a series of optoelectronic properties of the perovskite active layer. A uniform MAPbI3 film with highly crystalline qualities, large domain sizes, and few grain boundaries was realized with the introduction of graphdiyne. Moreover, the current–voltage hysteresis was negligible, and device stability was significantly improved as well. The results indicate that graphdiyne as the host active material presents great potential for the enhancement of the performance of perovskite solar cells.