Graphdiyne, a novel large pi-conjugated carbon hole transporting material, is employed as anode buffer layer in colloidal quantum dots solar cells. Power conversion efficiency is notably enhanced to 10.64% from 9.49% compared to relevant reference devices. Hole transfer from the quantum dot solid active layer to the anode can be appreciably enhanced only by using graphdiyne to lower the work function of the colloidal quantum dot solid. It is found that the all-carbon buffer layer prolongs the carrier lifetime, reducing surface recombination on the previously neglected back side of the photovoltaic device. Remarkably, the device also shows high long-term stability in ambient air. The results demonstrate that graphdiyne may have diverse applications in enhancing optoelectronic devices.