Facile Synthesis, Sintering, and Optical Properties of Single-Nanometer-Scale SnO2 Particles with a Pyrrolidone Derivative for Photovoltaic Applications

We investigate the preparation of mesoscopic SnO₂ nanoparticulate films using a Sn(IV) hydrate salt combined with a liquid pyrrolidone derivative to form a homogeneous precursor mixture for functional SnO₂ nanomaterials. We demonstrate that N-methyl-2-pyrrolidone (NMP) plays a crucial role in forming uniform SnO₂ films by both stabilizing the hydrolysis products of Sn(IV) sources and acting as a base liquid during nanoparticle growth. The hydrolysis of Sn(IV) was controlled by adjusting the reaction temperature to as low as 110 °C for 48 h. High-resolution TEM analysis revealed that highly crystalline SnO₂ nanoparticles, approximately 3-5 nm in size, were formed. The SnO₂ nanoparticles were deposited onto F-doped SnO₂ glass and converted into dense particle films through heat treatments at 400 °C and 500 °C. This pyrrolidone-based nanoparticle synthesis enabled the production of not only crystallized SnO₂ but also transparent and uniform films, most importantly by controlling the slow hydrolysis of Sn(IV) and polycondensation only with those two chemicals. These findings offer valuable insights for developing stable and uniform electron transport layers of SnO₂ in mesoscopic solar cells, such as perovskite solar cells.