Solution-combustion-based nickel oxide hole transport layers via fuel regulation in inverted planar perovskite solar cells

In recent years, metal oxide hole transporting layers (HTLs) have been commonly used in inverted planar perovskite solar cells. Due to high optical transmittance, better long-term stability, and suitable energy band characteristics, NiO x HTLs have been intensively studied. The NiO x materials prepared by solution-combustion method with characteristics of self-energy generation and exothermic reaction have received much attention, which significantly reduces the reaction temperature compared with the traditional sol–gel methods. In this paper, a NiO x film with better conductivity and enhanced carrier extraction was obtained by adjusting the fuel concentration in the nickel oxide precursor solution. It was also confirmed that perovskite film was improved with larger grain size and reduced trap-state densities. As a consequence, by using the 10 ul/ml optimal concentration of acetylacetone in the NiO x precursor solution, the inverted planar perovskite solar cells achieved a maximum power conversion efficiency of 14.37%.