The roles for fast electron injection and light harvests
Perovskite solar cells (PSCs) are promising alternative clean energy sources and will surely play a significant role in sustainable development and reducing overreliance on fossil fuels. As such, various strategies have been proposed to enhance their performance. Today, the energy conversion efficiency of perovskite solar cells is reportedly 25.2%, indicating that they are slowly emerging as new-generation energy sources. In particular, organic-inorganic lead iodide hybrid perovskite (MAPbI3) has drawn significant research attention owing to its remarkable properties. For instance, their long carrier diffusion length, which is approximately 175um, is longer than most common photovoltaic materials. This allows for efficient diffusion of free carriers between the electron acceptor layer and the MAPbI3 interface. Unfortunately, most of the converted energy in PSCs goes to waste, resulting in low energy conversion efficiency. The energy losses can be attributed to a longer electron injection time than that of thermalization.
Several strategies based on special materials such as graphene quantum dots have been proposed to overcome energy loss in the thermalization process by improving carrier extractions. Even though these materials have proved suitable for enhancing the device performance, the improvement of light-harvesting and carrier injection efficiency have not been fully explored. Recently, graphene-based composite materials have been extended to perovskite solar cells following their successful applications in chemical and physical fields. However, despite the good progress, the need for enhanced graphene composite materials to develop high-performance perovskite solar cells is still compelling.
On this account, Dr. Feng Gao and his research team (Mr. Ke Liu, Mr. Ruzhou Cheng and Mrs. Ying Zhang) from Shaoyang University fabricated a MAPbI3 perovskite solar cell based on graphene-CuInS2 quantum dots composite. Specifically, they investigated the performance enhancement of PSCs based on graphene-CuInS2 QDs composite. In their approach, CuInS2 was assumed to be a light-harvesting material owing to its low toxicity, large absorption coefficient, and small bandgap. Furthermore, the authors also explored the role of graphene-CuInS2 QT in improving both the light harvests and charge transfer processes in PSCs. Finally, possible charge transfer processes were discussed and proposed. The work is currently published in the research journal, Applied Surface Science.
The authors reported a significant enhancement of the charge transfer efficiency and the overall device performance due to the application of graphene-CuInS2 quantum dots composite. A significant improvement in the power conversion efficiency up to 17.1 was also observed. Besides, the resulting solar cells exhibited higher air stability and reproducibility. The high performance could be attributed to the improvement in the electron injection and light harvests. The charge transfer time was approximately 9 ns, as per the time-resolved photoluminescence measurements, which favored a higher energy injection rate. Furthermore, it was noted that the alignment of the energy level of graphene and MAPbI3 matched that of the CuInS2 quantum dots.
In summary, the preparation and synthesis mechanism of high-performance MAPbI3 PSC based on graphene-CuInS2 quantum dots composite was reported in the study. Most Importantly, the study highlighted the benefits of graphene-CuInS2 quantum dots composite in enabling an efficient electron transfer process in addition to its key traditional role as an electron acceptor. It also contributed immensely to the light-harvesting, thereby improving the overall solar cell performance. The results demonstrated that the graphene-CuInS2 QDs composite is a promising photovoltaic material for improving the performance of solar cells. Specifically, Dr. Gao, in a statement to Advances in Engineering, explained their study provides more opportunities for designing and fabricating high-performance solar cells.
Gao, F., Liu, K., Cheng, R., & Zhang, Y. (2020). Efficiency enhancement of perovskite solar cells based on graphene-CuInS2 quantum dots composite: The roles for fast electron injection and light harvests. Applied Surface Science, 528, 146560.