Monodispersed SnO2 microspheres aggregated by tunable building units as effective photoelectrodes in solar cells

Abstract Mesoporous SnO 2 microspheres assembled from densely-packed nanocrystalline building units are a class of useful nanomaterials and have extensive optoelectronic applications, but so far it is still a challenge to acquire monodispersed microspheres. Here, monodispersed SnO 2 microspheres consisted of aggregated small primary nanocrystallites are synthesized via a surfactant-free solvothermal method. These SnO 2 microspheres have high specific surface area, excellent crystallinity and tunable building units. By precisely controlling the nucleation and growth, the obtained microspheres exhibit narrow size distribution, whose diameters are 200 ± 17 and 191 ± 16 nm from pure n-propanol and n-propanol/water mixed solvents, respectively. The sizes of primary nanocrystals slightly increase with the adscititious water. The SnO 2 microspheres exhibit large specific surface areas, leading to efficient sensitizer-loading in both dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). The sub-micron-sized microspheres could also enhance the light-harvesting of the solar cells due to their light-scattering capability. As the primary nanocrystal multiply contacts densely to neighbouring grains, such intergrowth would improve the electron transport through the grain boundaries. Eventually, a power conversion efficiency of 3.83% is yielded for pure SnO 2 -based DSSCs when the SnO 2 microspheres are used as the scattering layers, and an efficiency of 15.41% is obtained when they are used as the electron transport layers in PSCs.