Non-hydrolytic sol-gel route to synthesize TiO2 nanoparticles under ambient condition for highly efficient and stable perovskite solar cells

For developing low-temperature processed electron-transporting layer in perovskite solar cells, titanium oxide (TiO2) nanoparticle was synthesized through the non-hydrolytic sol-gel route. TiO2 nanoparticles showed uniform film coverage, high transparency in the visible region with wide optical bandgap, and high electrical conductivity after systematically optimizing the synthetic reaction time, the thermal annealing temperature, and the concentration of Nb doping. When TiO2 nanoparticle was introduced as an electron-transporting layer through low-temperature deposition process, the perovskite solar cells fabricated in ambient conditions showed high efficiencies of 18.97% and 13.51% on the rigid glass and the flexible plastic substrate, respectively. An impressively high open circuit voltage of 1.17 V and short circuit current density of 22.21 mA cm(-2) were achieved due to the well aligned work function and better electrical conductivity of Nb-doped LT-TiO2 layer. Importantly, solar cells fabricated with TiO2 nanoparticle showed high thermal stability, negligible hysteresis, and reduced charge recombination loss at electron-transporting layer/perovskite interfaces. This study shows that TiO2 nanoparticle can be obtained through the low cost and facile synthesis and has high potential as an electron-transporting layer for low-temperature processable perovskite solar cells.