In this work, a simple and convenient interface modification by nanosized diamond (ND) was used in the carbon based all-inorganic CsPbIBr 2 planar perovskite solar cells (PSCs). Only by spin-coating ND particles on the crystallized perovskite without further treatment did all CsPbIBr 2 PSCs achieve an overall improvement in photovoltaic performance. The champion PCE of ND modified PSC reached 9.07%, 22% higher than the control device (7.46%), and remained at 86% of its original value after 50 days. Particularly, the device obtained a V OC beyond 1.30 V and FF over 60% at the same time, which is superior to most of the reported CsPbIBr 2 PSCs. The results of light absorption, PL spectra, TPC, TPV, and electrochemical analysis revealed that the superior device performance mainly came from the improved light absorption and reduced carrier recombination in PSCs. Therefore, the ND provides a facile strategy to enhance the performance of CsPbIBr 2 PSCs.