[21a-432-1~12] 12.5 Organic solar cells

▲ [21a-432-1] Performance of planar perovskite solar cells with mixed C60/C60 electron transport layer: an ab initio rationalization

Amrita Pal¹, 〇Sergei Manzhos¹, Hao-Sheng Lin², Il Jeon², Rong Xiang², Seungju Seo², Jin-Wook Lee³, Chao Li³, Mark Goorsky³, Yang Yang³, Shigeo Maruyama², Yutaka Matsuo^2,4 (1.Ntl. Univ. Singapore, 2.Univ. of Tokyo, 3.UCLA, 4.USTC Hefei)

Keywords:perovskite solar cells, fullerenes, ab initio modeling

Planar perovskite solar cells have now achieved efficiencies on par with their sensitized counterparts. High performance planar perovskite cells utilize C60 as the electron transport layer (ETL) deposited using costly thermal evaporation. Recently, a mixed C60 and C70 solution-processed film with low crystallinity has been proposed as an ETL. The mixed-fullerene-based devices with a C60:C70 ratio of 9:1 achieved a similar or higher performance compared to their thermally evaporated C60 based counterparts.
Here, we present a density functional theory - density functional tight binding study of molecular and solid C60, C70, and the mixed system, aiming to rationalize these results. We show an excellent band alignment for electron transport of C60 and C70 components in solid state. The mixing energy of C60 and C70 components is computed to be on the order of kT at room temperature, implying absence of significant driving force to either segregation or desegregation. We also show a negligible effect of interfaces on the band structure. The computed electron transfer rates (using Marcus model) can be achieved with the C60/70 mixed structure are on the order of 10¹² sec^-1, similar to pure C60.