Triple Cathode Buffer Layers Composed of PCBM, C<sub>60</sub>, and LiF for High-Performance Planar Perovskite Solar Cells

In this paper, triple cathode buffer layers (CBLs) composed of phenyl-C<sub>61</sub>-butyric acid methyl ester (PCBM), C<sub>60</sub>, and LiF layers were introduced into the planar p–i–n perovskite solar cells (p–i–n PSCs) with a device structure of ITO/PEDOT:PSS/CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub>/CBLs/Al. For comparison, a single CBL of PCBM and a double CBL of PCBM/LiF were also investigated in the p–i–n PSCs. On the basis of the PCBM buffer layer, the addition of a thin LiF layer facilitated the charge collection process and led to the dramatic improvement of the power conversion efficiency (PCE) of the PSCs up to 14.69% under an illumination of AM 1.5G, 100 mW/cm<sup>2</sup>, which is to date one of the highest efficiencies of the p–i–n PSCs. By further insertion of a C<sub>60</sub> layer between PCBM and LiF in the triple CBLs, a PCE of 14.24% was obtained, and more importantly, the PCBM/C<sub>60</sub>/LiF triple CBLs are very helpful for improving the stability of the devices and making the LiF layer less thickness-sensitive for achieving high performances of the p–i–n PSCs.