Printable oil-NiO_X hole transport layer enables efficient n-i-p perovskite solar cells with a high thermal stability

Currently, highly efficient n-i-p perovskite solar cells rely on an organic interface layer for high efficiency, especially 2,2′,7,7′-tetrakis [N,N-bis(4-methoxyphenyl) ami-no]-9,9′-spirobifluorene (spiro-OMeTAD), but the instability of organic materials in the photothermal field compromises device stability. In this study, we employ the oleic acid (YS)/oleamine (YA) end-sealing method to achieve uniform dispersion of NiO_X nanoparticles, effectively mitigating coagulation resulting from high local concentration and secondary motion adsorption. Furthermore, the conductivity of the hole transport layer and its energy level alignment with perovskite is enhanced by the additional 2,3,5,6-tetrafluoro-7,7′,8,8′-tetracyanodimethyl-p-benzoquinone (F4TCNQ), leading to a remarkable improvement of open-circuit voltage and fill factor, thus the high efficiency of 25.17% and 24.36% on 0.1 and 1.01 cm², respectively. Moreover, by realizing an all-inorganic interface layer, an initial efficiency exceeding 90% is maintained even after 2,800 h of heating at 85 °C.