Alkyl Chain Length-Dependent Amine-Induced Crystallization for Efficient Interface Passivation of Perovskite Solar Cells

Efficient surface passivation of perovskite solar cells (PSC) using treatment with ammonium salts is demonstrated as an efficient method to enhance the device performance, owing to the affinity between the amine group and [PbI6](4-) octahedron. However, due to their high solubility in polar solvents (DMF/DMSO), ammonium salts are more difficult to use in passivation of the interface between the electron transport layer and perovskite thin film in n-i-p structured PSCs. In this report, this work successfully links the amine group with a fullerene through a series of increasing carbon chain length, from two to twelve methylene units (FC-X, X = 2, 6, 12), and then introduce the synthesized molecules as interface passivation layers into SnO2-based planar n-i-p PSCs. Results show that the interface passivation effect is highly dependent on the side-chain length, and the longer chain length amine-functionalized fullerene is more beneficial for the device performance. A power conversion efficiency as high as 21.2% is achieved by using FC-12. The surface energy, perovskite crystallite size and electron transfer capacity correlate with the linker chain length. This work develops an amine-induced anchored crystallization of perovskite to unravel the mechanism of this passivation effect. As expected, enhanced device stability is also observed in the FC-12 passivated PSCs.