Improved contact of “Spiro-OMeTAD/perovskite” interface by hydrophilic 1, 6-hexanediammonium diiodide molecule and the accelerated charge extraction processes

Hydrophilic 1, 6-hexanediammonium diiodide (HDADI) is used to modify the perovskite surface, so as to improve the contact between the “Spiro-OMeTAD/perovskite” interface. It is observed that, after moderate HDADI modification, the wettability of Spiro-OMeTAD/chlorobenzene solution on perovskite is improved. After modified at moderate concentration of HDADI, surface roughness of perovskite film decreases from 19.4 to 15.8 nm, while that of Spiro-OMeTAD (coated on perovskite) decreases from 7.54 to 6.53 nm, indicating better interfacial contact. The improved interfacial contact is due to the hydrophilic nature of the HDADI molecule, and the formed two-dimensional (2D) Dion–Jacobson phase perovskite, as revealed by x-ray diffraction and x-ray photoelectron spectroscopy studies. Photoluminescence and Mott–Schottky studies show that defects are reduced. Accordingly, the charge-extraction rate is accelerated, while recombination is reduced according to transient photovoltaic/photocurrent decay curves tests and impedance spectroscopy. Photo-to-electric power conversion test demonstrates that the modification helps upgrade the power conversion efficiency of perovskite solar cells from 20.25 (±0.85)% to 22.28 (±0.53)% (with a champion efficiency of 23.08%). In addition, device stability has also been prolonged. This study provides an efficient strategy to strengthen the contact between the “Spiro-OMeTAD/perovskite” interface.