Facile scalable synthesis of MoO₂ nanoparticles by new solvothermal cracking process and their application to hole transporting layer for CH₃NH₃PbI₃ planar perovskite solar cells

∼10 nm sized MoO₂ nanoparticles with high BET surface area of 170.14 m²/g were synthesized via scalable new process of combining the ultrasonic spray pyrolysis and solvothermal cracking process. Initially, we synthesized polycrystalline MoO₃ microparticles by the ultrasonic spray pyrolysis at 500 °C or 600 °C. Then the MoO₃ microparticles were disassembled into crystalline grains and the grains were subsequently shattered to small MoO₂ nanoparticles through the solvothermal polyol reduction process because the polycrystalline MoO₃ microparticles are disassembled by thermal expansion and the crystalline MoO₃ grains are shattered by volume shrinkage due to phase transition from MoO₃ to MoO₂. Finally, we applied the MoO₂ nanoparticles/toluene solution to new inorganic hole transporting material for planar CH₃NH₃PbI₃ perovskite solar cells. The planar type CH₃NH₃PbI₃ perovskite solar cells exhibited stable efficiency of 14.8% for forward scan condition and 15.5% for reverse scan condition under illumination of 1 Sun (100 mW/cm²).