Low-temperature welding engineering of ZnO nanoparticles films via sol-gel method

ZnO nanoparticles is a highly promising semiconductor material as an electron transfer layer layer (ETL) in various optoelectronic devices. The cost-effective and low-temperature preparation method renders it ideal for the development of flexible and large-scale modules, aligning seamlessly with the commercialization process. However, Solution-derived ZnO exhibits a significant number of surface defects, which affect the device's photoelectric conversion performance and stability. Herein, a simple strategy focusing on controlling the nano size of ZnO was employed to mitigate these surface defects. Welded ZnO films were prepared via spin coating with a precise amount of ZnO sol into dispersion. These films were characterized via techniques such as TEM, FSEM XRD, DLS, UV/vis and so on. PL spectra revealed a notable decrease in defect density with the increase in nano size. AFM reveals that films doped with 15 % sol exhibit root mean square (RMS) values of less than 1 nm, indicative of improved smoothness. Moreover, the four-point probe detected enhanced electrical conductivity attributed to the compact structure and improved integrity of the films. The presence of nanoparticles facilitates the crystallization of ZnO sol, allowing for an annealing temperature during the welding process to as low as around 90°C, compatible with flexible plastic substrates such as PET. The welded ZnO films produced at a low temperature in this study demonstrate high potential as ETL for flexible optoelectronic devices, which is conducive to their commercialization and large-scale deployment.