Unravelling the role of C₆₀ derivatives as additives into active layer for achieving high-efficiency planar perovskite solar cells

Fullerene derivatives have been proved to be useful as additives into active layer to improve perovskite solar cells (PSCs) performance in the power conversion efficiency, stability and reproducibility. In this work, to unravel the influences of chemical compositions of fullerene derivatives on the PSCs performance, we systematically compare a series of fullerene-derivatives additives, including C₆₀, PCBM and C₆₀-Taurine. Two important conclusions are achieved: (i) the bare C₆₀ cage primarily plays a role to accelerate the electron extraction and transport; (ii) the side chains adhered to the C₆₀ cage could further help to improve the stability of PSCs by reducing the defect states and improving the perovskite crystalline quality. It is also noteworthy that these two goals may be hard to be simultaneously achieved because the insulation property of side chains leads to the decline of electron extraction capacity. Therefore, an intelligent design of fullerene derivatives as the additives is strongly suggested to balance the stability and PCE.