Abstract
Perovskite solar cells (PSCs) has been reached the certified power conversion efficiency (PCE) of 25.2 % in 2019. They are having received large attention because of their superior optoelectronic properties (such as high charge carrier mobility, tunable bandgap, high absorption coefficient) and even the cost-effective process.In the latest fabrication process for high-efficiency PSCs, surface-defect engineering of perovskite film has attracted tremendous attention. Because, the control of surface-defects can play a critical role in grain boundaries of perovskite, and interfaces between perovskite and charge transport layer, leading to PSCs with further improved photovoltaic (PV) performance and long-term stability. There are many exertion for reducing surface-defects state densities of perovskite film by applying an additional passivation layer, for instance cross-linked molecules and two-dimensional (2D) materials (2D-perovskite, graphene, and MoS2) at surface of perovskite film.Most recently, perovskite nanocrystals (NCs) are being investigated as an additional layer for high-efficiency PSCs owing to anticipation of their multifunctional properties including high light-harvesting properties, efficient charge transport by carrier cascade effect, and surface passivation effect. However, it seems to remain under question whether these functions are related to the light-harvesting, suitable band alignment, and surface passivation for PSCs, due to ligand capped NCs.In this study, we investigated that the functions of NCs layer in PSCs with various NCs capped same ligand. To confirm the effects of NC layer in PSCs, we fabricated n-i-p planar devices, which follow FTO/c-TiO2/Perovskite/NC layer/Spiro-OMeTAD/Au structure with three kinds of NCs (CsPbBr3, CsPbI3, and InP). All these NCs have different electrical and optical properties, but nevertheless the devices with each NC layer showed similarly improved PV performance.In analysis results of each function of the NC layer, there were no light-harvesting effects by all NCs layer due to high absorption coefficient and sufficient thickness of perovskite film. In addition, NC layer could not work as a carrier cascade layer at the interface between the perovskite film and hole transport layer due to poor electrical properties of capping ligand. Finally, the NC layer affected only on the surface passivation of perovskite film, and furthermore we found that Oleylamine (OLA) ligand of the NCs was a major cause of the surface passivation effect. We believe that the optimization of the surface passivation effect of fatty amine ligands can further improve the PV performance of PSCs.
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