Density Functional Theory Investigation of Carbon Dots as Hole-transport Material in Perovskite Solar Cells

Charge transfer in solar cells is crucial, and so is the hole transporting layer (HTL) component in perovskite solar cells (PSCs). Finding a suitable material for this purpose that is inexpensive - either organic or inorganic - is currently one of the prime research objectives to improve the performance, through charge transfer dynamics, of PSCs.< One such recent finding is carbon quantum dots (C-dots), which is a simple and low-cost organic material that could be an alternative option to the currently employed high-cost and complex-structured hole transporting materials (HTMs) utilized in perovskite solar cells. A series of C-dots functionalized with hydrogen, hydroxyl (-OH), and carboxyl (-COOH) groups are considered in this study for their hole-transporting properties. The results reveal that simple hexagonal structured C-dots including -OH and -COOH group substituted C-dots have suitable valance band maximum (VBM) positions, which are suitable for hole transport. It is discovered that the position of the functional moieties on the C-dots would impact the band-edge positions of the C-dots. This implies that tuning the band position is possible so that these two-dimensional C-dots could, in principle, be used for other solar-cell applications that may require different band positions for optimal performance. As a representative example, we studied the perovskite/C-Dot interface of two different possible surfaces (i. e. MAI and PbI₂ terminated perovskites) combined with a hexagonal C-Dot layer and found that there is a good probability of charge transfer between the perovskite layer and the C-dots, which promotes hole transfer between the perovskite and the C-dots.Introduction.