As more attention and investment goes into solar energy, researchers are trying to develop better alternatives to the currently most widely used silicon-based solar cells. Silicon solar cells have high manufacturing and energy costs, hence a new more cost-effective technology is required. One of the best candidates is perovskite-based solar cells. These can be produced more cheaply using simpler manufacturing methods and the end product has comparable power conversion efficiency (PCE) [1].
For perovskite solar cells to work efficiently it is necessary to have layers that separate positive and negative charges, which are being generated in the perovskite light absorber, so they do not recombine [2]. Materials that carry positive charges, called hole transporting materials (HTMs), typically limit solar cells’ efficiency. Currently one of the most perspective HMTs are those able to form a self-assembled monolayer (SAM). Solar cells with SAM hole transporting materials tend to have higher efficiency, lower HTM consumption and can be used for the manufacture of silicon/perovskite tandems to reach even higher PCE.
SAM forming HTMs are organic molecules, therefore it is possible to easily modify them to be more compatible with the perovskite layer. In this work, we demonstrate, how HTMs can be adapted to perovskites of different compositions, by modifying chemical structure. Using carbazole-based HTM in lead-based perovskites we have achieved high – 20.9% PCE. By changing carbazole to phenoxazine derivative we have achieved relatively high 7.7% efficiency in tin-based perovskite devices.
In summary, this research shows that by modifying central fragments of hole transporting materials, we can adapt them to different perovskite formulations and achieve improved efficiencies, thus making perovskite solar cell technology more viable for commercial use.