Achieving high performance and stable inverted planar perovskite solar cells using lithium and cobalt co-doped nickel oxide as hole transport layers

Perovskite solar cells (PSCs) have become an impressive research focus due to their unique properties, where their interface transport layers are important for an enhancement in efficiency and stability. In this study, we demonstrate that a lithium (Li) and cobalt (Co) co-doped NiO_x hole transport layer can greatly enhance the device performance of inverted planar heterojunction PSCs. Compared to the pristine NiO_x films and Li doped NiO_x HTLs, co-doping with a certain amount of Li and Co further increased the electrical conductivity and hole mobility of the NiO_x film. Consequently, the power conversion efficiency (PCE) of the PSCs greatly improved from 17.4% to 20.1% when they were co-doped with 10% Li and 5% Co. Moreover, the short-circuit current density (J_sc) increased from 22.7 mA cm^-2 to 23.8 mA cm^-2, the open-circuit voltage (V_oc) was enhanced from 1.05 V to 1.09 V, and the fill factor (FF) was enhanced from 0.73 to 0.78 for the PSCs. These results demonstrate that the co-doping of Li and Co can be an effective strategy improving the performance of PSCs.