First Conventional Solution Sol-Gel-Prepared Nanoporous Materials of Nickel Oxide for Efficiency Enhancing and Stability Extending MAPbI3 Inverted Perovskite Solar Cells

With a judicious selection of the nickel complex (precursor) and stabilizer, that is, nickel formate and enthylenediamine, respectively, a conventional sol-gel method followed by a sintering process at 450 °C, nanoporous NiOx(np-NiOx) thin films have been successfully prepared. However, the alcohol solvent used in the sol-gel process is critical that only low-viscosity ones, such as methanol, ethanol, 2-methoxyethanol, and iso-propanol, afford np-NiOxinstead of plate/flake-like compact NiOx(cp-NiOx). Some stabilizers, such as 1,3-diaminopropane, diethylenetriamine, andN,N-dimethylethylenediamine, provide nothing but seemly amorphous NiOxfragmentary thin films, which are unsuitable for the hole-transporting material (HTM) in the inverted perovskite solar cells (PVSCs). SEM or AFM study has a clear differentiation between np-NiOxand cp-NiOx. Moreover, we have characterized that the np-NiOxthin films show a better conductivity, a higher hole mobility, a stronger perovskite photoluminescence quenching, and a superior transparency than those of cp-NiOxthin films. Using MAPbI3, inverted PVSCs were fabricated with either np-NiOxor cp-NiOxas HTM. A high power conversion efficiency approaching 20% was achieved by np-NiOx-based PVSCs, which was better than our best PVSC (17.95%) based on cp-NiOx. Electrochemical impedance spectroscopy (EIS) has observed a lower charge recombination resistance but a higher charge transport resistance for the cp-NiOxdevice comparing with those of each np-NiOxdevices. Moreover, np-NiOxMAPbI3PVSCs exhibit a less hysteresis effect and an extended lifetime in terms of shelf stability compared with those of cp-NiOxMAPbI3PVSCs. The SEM and XRD have demonstrated the larger grain size and less gain boundary of MAPbI3thin films on np-NiOxHTM, where MAPbI3is in fact more hydrophobic, evident by the water contact angle. ? 2021 American Chemical Society