Low temperature ALD growth optimization of ZnO, TiO2, and Al2O3 to be used as a buffer layer in perovskite solar cells

Organic materials provide a very small thermal budget for any postfabrication treatment or for a subsequent layer in a device fabrication. This demand for the low-temperature process has driven the focus of this study to obtain atomic layer deposited oxide layer at a low temperature suitable for a buffer layer in perovskite solar cells. The buffer layer will assist in blocking holes, effectively extract electrons, provide better shunt protection, and act as a sputter protection layer for organic perovskites. Three different oxide layers, Al2O3, ZnO, and TiO2, are grown at 100 degrees C and studied for this purpose using synchronous modulated flow draw atomic layer deposition (ALD) technology optimized in a commercial 200mm ALD reactor from Sundew Technologies. It allows greater precursor utilization and shorter deposition cycle times that in turn reduces thermal processing time compared to traditional ALD processes. These thin films have been shown to enhance the fill factor and high charge extraction from the solar cell. Three oxides are compared on all aspects, among which ZnO (3nm) along with Al2O3 (1nm) on top of the perovskite layer have shown excellent performance improvement in the device's power conversion efficiency.