Researchers from the Graphene Flagship, working at the Istituto Italiano di Tecnologia (IIT) and the University of Rome Tor Vergata, show that interface engineering with layered materials is important for boosting perovskite solar cell performance and that the lifetime of perovskite solar cells is significantly enhanced by using few-layer molybdenum disulphide (MoS2) flakes (a semiconductor material with a layered structure).
The team managed to significantly enhance the stability of perovskite solar cells (PSCs) by including few-layer MoS2 flakes as an active buffer layer in the cell design. These PSCs retain 93% of the initial light conversion efficiency after 550 h, compared to only 66% for cells without the MoS2 buffer layer. This represents an important step towards viable PSCs, especially as the addition of the MoS2 interface layer is compatible with low-cost solution processing techniques.
In this research, 200'600 nm wide flakes of few-layer MoS2 were added into the solar cell device as a buffer layer in between the photoactive perovskite and hole-collecting layers, delivering high stability and increased photovoltaic performance. The spray-coating of the MoS2 flakes does not add complex fabrication steps to the PSC production. The 1.05 cm2 cells demonstrated show that the high stability solar cells can also be fabricated in large area formats, a vital condition for real-world application.
The MoS2 buffer layer acts in two ways to keep the high solar conversion efficiency stable over time. Firstly, the MoS2 provides an effective interface between the perovskite and the hole transporting layer, due to its high hole mobility and good energy matching with the perovskite. This leads to the high initial efficiency of the cell, by reducing recombination of the electrons and holes that are generated by light conversion in the perovskite. Secondly, the MoS2 buffer prolongs the life of the perovskite layer by preventing degradation and ion migration from the electrode. This also protects against direct electrical contact with the gold electrode which collects the photocurrent, ensuring that the high efficiency is maintained over time.
This research indicates that there are significant opportunities for using layered materials to boost performance for renewable energy generation. By increasing the stability and usable lifetime of perovskites, the goal of viable PSCs is a step closer.