Recently, the research team led by Prof. Liu Shengzhong and Dr. Yang Dong of Shaanxi Normal University's School of Materials Science and Engineering, has prepared a high-performance planar-type perovskite solar cell with ionic liquid (IL) modification TiO2 as the electron transport materials (ETLs), and the efficiency of their solar cells is as high as 19.62%, the highest value ever reported so far for planar-type devices.
In the last few years, organometal-trihalide perovskites have been recognized as the most promising absorber materials for low-cost, high efficiency solar cells because of their superior properties including strong light absorption, long range charge-carrier diffusion, high carrier lifetime, and apparent tolerance to defects. The ETL with excellent photoelectronic properties is very crucial in high performance of perovskite solar cells.
In their previous work, the team used the IL with high electron mobility and good transmittance as ETL to fabricate the flexible perovskite solar cells and the efficiency reached 16.09%, the highest value reported by that time. (Adv. Mater., 2016, 28, 5206-5213)
This time, they employed the IL modification TiO2 (m-TiO2) as ETLs to fabricate the hysteresis-free planar-type perovskite solar cells and the efficiency reached as high as 19.62%, the highest value reported so far for planar-type devices. The electron mobility of TiO2 ETL is enhanced and its Fermi level moves upward after IL modification, which is beneficial to the export of the electrons in the device. Both experimental analyses and theoretical calculations reveal that the anion group of the IL bonds to TiO2, leading to higher electron mobility and well-matched Fermi level. Meanwhile, the cation group interfaces with adjacent perovskite grains to provide an effective channel for electron transport and a suitable setting to grow low trap-state density perovskite for improved device performance. In light of the effective surface modification, which is so straightforward and economic, it is anticipated to be viable for large-scale roll-to-roll production.
The research was recently published under the title “Surface optimization to eliminate hysteresis for record efficiency planar perovskite solar cells” in the journal Energy & Environmental Science (Impact Factor: 25.427) (Energy Environ. Sci., 2016, DOI: 10.1039/C6EE02139E).