The Functions of Fullerenes in Hybrid Perovskite Solar Cells

There is increasing interest in the application of fullerene-based carbon materials in perovskite solar cells for increased efficiency, reduced hysteresis, and improved stability. This Perspective summarizes the progress in the understanding of the function of fullerenes in perovskite solar cells in blocking leakage through pin-holes, passivating the defects at the perovskite film surfaces and grain boundaries, and modulating the open-circuit voltage of the devices. We also critically reviewed several open questions on the functions of fullerenes in perovskite solar cells based mainly on recent progress: How do fullerenes reduce current hysteresis? What is the function of double-fullerene layers? Does the doping of the fullerene by perovskite contribute to eliminating the photocurrent hysteresis at room temperature? Why do some perovskite/fullerene solar cells still have hysteresis at low temperature? Are perovskite solar cells with fullerenes in the intergranular boundaries bulk heterojunction solar cells? Finally, the impact of the fullerene on perovskite solar cell stability is discussed.