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 PbI 2 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.