Recently,silicon-based solar cell research group led by Prof. Can Li and Prof.Shengzhong Liu of Dalian National Laboratory for Clean Energy Lab cooperateswith Dr. Dong Yang of Shaanxi Normal University to prepare a planar-type perovskitesolar cell with ionic liquid (IL) modification TiO2 as the electron transportmaterials (ETLs), and the efficiency is up to as high as 19.62%, the highest valueto report so far for planar-type devices. The related results were publishedonline in the journal of Energy & Environmental Science. (Energy Environ.Sci. DOI: 10.1039/C6EE02139E)
In the last few years, a feworganometal-trihalide perovskites have been recognized as the most promisingabsorber materials for low-cost, high efficiency solar cells because of theirsuperior properties including strong light absorption, long rangecharge-carrier diffusion, high carrier lifetime, and apparent tolerance to defects.The ETL with excellent photoelectronic properties is very crucial in highperformance of perovskite solar cells. In previous works, we used the IL withhigh electron mobility and good transmittance as ETL to fabricate the flexibleperovskite solar cells, and the efficiency reaches to 16.09%, the highest valueto report so far.
In this work, we employ the IL modificationTiO2 (m-TiO2) as ETLs to fabricate the planar-typeperovskite solar cells, the efficiency reaches to as high as 19.62% with hysteresis-free,the highest value to report so far for planar-type devices. The electronmobility of TiO2 ETL is enhanced and its Fermi level moves upward afterIL modification, which is beneficial to the export of the electrons in thedevice. Both experimental analyses and theoretical calculations reveal that theanion group of the IL bonds to TiO2, leading to higher electronmobility and well-matched Fermi level. Meanwhile, the cation group interfaces withadjacent perovskite grains to provide an effective channel for electrontransport and a suitable setting to grow low trap-state density perovskite forimproved device performance. Considering that this surface modification is sostraightforward and economic, while it is so effective, it is anticipated to beviable for large-scale roll-to-roll production.
Thiswork has been financially supported by National Key Research Program of China, NationalNatural Science Foundation of China, 111-Project, Chang jiang Scholar and. (Article/Figure, Doudou Zhang, DongYang) 
