Atomic layer deposition (ALD) is now being recognized as a powerful, general tool for modifying the surfaces of nanomaterials in applications for many renewable energy conversion devices. However, ALD involves slow processes particularly when it is subjected to nanoporous media with high-aspect ratios. A comparative study of the ALD coating onto two distinctive templates having nanopores, i.e., two- and three-dimensionally ordered media (DOM), of similar porosity and pore dimension. Comparison of the ALD coating profiles across the thickness of both templates reveals fundamentally distinct coating mechanism; while a uniform growth zone develops along the pores of the 2-DOM (i.e., 1-D diffusion path), a gradual decrease in the deposition is observed in those of the 3-DOM (i.e., 3-D diffusion path) as ALD pulse time increases. This observation suggests an essential role of the pore connectivity, rather than individual pore sizes, in the gas diffusion dynamics inside nanoporous media. The present model study helps universally predict the ALD behaviors into nanoporous media even with different types of pore connectivity.
CH3NH3PbI3 with perovskite crystal structure has attracted considerable interest for high power conversion efficiency (PCE). ALD chemistry for TiO2 and ZnO are well known and the process requires relatively low deposition temperature as low as ~ 100 °C, even possible at 50 °C, which is applicable to deposit onto the halide perovskite layer. In this presentation, highly efficient perovskite solar cells having a long-term stability that adapts uniform and dense inorganic charge transport layer (NiO as hole transporting layer and TiO2 and ZnO as electron transporting layers) grown by atomic layer deposition (ALD) are reported. Highly dense inorganic electron transport layers (ETL) have been deposited onto the perovskite absorbing layer using ALD process at relatively low temperature (100 oC). The devices shows excellent water-resistant properties and long-term stability at 85 °C under illumination compared to devices without ETL grown by ALD.