Hole-Transport Materials Containing Triphenylamine Donors with a Spiro[fluorene-9,9′-xanthene] Core for Efficient and Stable Large Area Perovskite Solar Cells (Solar RRL 9∕2017)

The perovskite solar cell is one of the most promising next-generation solar cells. The best performing solar cells use a hole-transport material called "spiro-OMeTAD". The problems associated with this hole-transport material are its high cost and poor durability. Here, Wu et al. (article No. 201700096) have developed new hole-transport materials of which the production cost estimated to be about 1/3 of that of spiro-OMeTAD. These new hole-transport materials worked nearly as well as spiro-OMeTAD. The HOMO energy levels were estimated to be −5.34 to −5.37 eV, which are higher than the valence band w a hole-extraction layer from the photoexcited perovskite. The LUMO energy levels are much higher than the conduction band edge of the perovskite, which makes these materials suitable as an electron-blocking layer. Finally, the efficiencies of the cells with the new hole-transport materials were the same or even exceeded the efficiency of a spiro-OMeTAD-based cell at the 10th day after fabrication, which shows that the new hole-transport materials are better in terms of on-the-shelf durability than spiro-OMeTAD.