Perovskite solar cells based on self-assembled monolayer materials for charge transport achieve high efficiency. However, the control of the electrical properties and coverage of these few nanometre-thick monolayers is challenging. In particular, the morphology of the underlying substrate — a transparent conductive oxide electrode — has been reported to affect the quality of the layer. Yet, a deeper understanding of the factors at play is needed. Now, Suzana Kralj, Monica Morales-Masis, and team at the University of Twente and King Abdullah University of Science and Technology show a correlation between the microstructure of the electrode and the work function — the minimum energy needed to extract an electron from the surface of a material — of the self-assembled monolayers.
The researchers compare conductive oxide electrodes with different microstructures, that is, amorphous and polycrystalline with nanometre- or micrometre-scale grains. The large grain size and different crystal orientations of the polycrystalline sample with micrometre grains lead to an inhomogeneous spatial distribution of the work function. Such inhomogeneity is retained when the self-assembled monolayer is deposited on top of the electrode, making charge transport less effective. On the other hand, Kralj et al. show that the use of amorphous buffer layers, such as nickel oxides, could ensure a uniform work function when using polycrystalline electrodes. They conclude that electrodes or buffer layers with an amorphous structure or no preferential crystal orientations are needed to afford high-efficiency solar cells.
This is a preview of subscription content, access via your institution