Graphdiyne-modified cross-linkable fullerene as an efficient electron-transporting layer in organometal halide perovskite solar cells

Interface engineering resulting in good contact, enhanced transport capability, and matched energy levels is indispensable and critical for the development of high-performance planar perovskite solar cells (PSCs). Here, we report an excellent electron-transporting layer (ETL) that can simultaneously enhance the stability and efficiency of n-i-p planar PSCs. Large pi-conjugated graphdiyne (GD) was introduced into cross-linkable fullerene [6,6]-phenyl-C61-butyric styryl dendron ester (PCBSD) to improve the film orientation. Raman spectroscopy and 2D grazing incidence X-ray diffraction (GIXRD) measurements revealed that a strong pi-pi stacking interaction occurred between GD and cross-linkable PCBSD (C-PCBSD), generating a face-on stacked composite film. The orientated C-PCBSD: GD films was favorable for the growth and crystallization of the subsequent perovskite films and provided the merits of superior electron mobility, efficient charge extraction and energy-level tailoring. In addition, the thermally annealed C-PCBSD: GD film provided an adhesive film network with sufficient solvent resistance. Consequently, the perovskite devices delivered a power conversion efficiency of 20.19% with obviously improved cell stability. This indicates a potential application of GD-modified cross-linkable fullerene as an ETL in n-i-p structure PSCs. The finding opens a new route to deposit the fullerene films with ordered orientation by 2D materials with large pi-conjugation, and thus to control the subsequent perovskite crystallization.