Preparation of Zn2+ doped NiCo2O4: Hole transport layer for high performance of perovskite solar cells

Inorganic hole transport materials (HTMs) play an important role for the stability and efficiency of planar perovskite solar cells (PSCs). Among the numerous inorganic HTMs, NiCo 2 O 4 with its excellent performance is the emerging candidate for hole transport layers (HTLs) and is attracting increasing attention. However, the low electrical conductivity and optical transmittance of NiCo 2 O 4 severely limit the device performance. Herein, the Zn 2+ was used to dope NiCo 2 O 4 to improve the electrical conductivity and optical transmittance of NiCo 2 O 4 . And the effects of the concentration of Zn 2+ on the morphology, structure and properties of NiCo 2 O 4 were investigated. The morphology and transparency of Zn x Ni 1-x Co 2 O 4 would not be affected when the concentration of Zn 2+ is below 0.1, but when it is up to 0.15 and 0.2, the morphology of NiCo 2 O 4 clustered together or showed a diamond-shaped block, and the optical transmittance also decreased significantly. Meanwhile, with the increase of doping amount, the conductivity and hole mobility are gradually increased. As a result, the optimal concentration of Zn 2+ is 0.1. Besides, the Zn 0.1 Ni 0.9 Co 2 O 4 possessed a significant improvement in hole extraction and better band alignment compared to the NiCo 2 O 4. And hence, the power conversion efficiency (PCE) of PSCs fabricated in open air is up to 13.41% by using Zn 0.1 Ni 0.9 Co 2 O 4 . This work develops a potential strategy for developing highly efficient and stable PSCs, opens up a new horizon for the development of inorganic HTMs.