[6a-A501-1~12] 12.5 Organic solar cells

▲ [6a-A501-1] Comparative computational study of fullerene derivatives: effects of addends, buckyball size, and crystallinity on bandstructure, charge transport, and optical properties

Amrita Pal¹, Lai Kai Wen¹, Chia Yao Jun¹, 〇Sergei Manzhos Manzhos¹, Il Jeon², Yutaka Matsuo² (1.Natl Univ Singapore, 2.University of Tokyo)

Keywords:fullerenes, planar perovskite solar cells, organic solar cells

We present a systematic comparative Density Functional Theory (DFT) – Density Functional Tight Binding Study (DFTB) of multiple derivatives of C60 and C70 with different addends, in molecular as well as solid state. Specifically, effects due to fullerene size, type and number of addends, and of crystallinity on bandstructure, charge transport, and optical properties are investigated. These are important, in particular, for rational selection of fullerene derivatives as acceptor and electron transport layers in organic as well as planar perovskite solar cells. We find that by the choice of type and number of addends, one can modulate the LUMO within 0.4 eV. Changes in the HOMO can reached 0.6 eV. Substituting C70 for C60 results in destabilization of the HOMO by about 0.1 eV for indene and quinodimethane addends and by a less significant amount for PCBM addends. The effect of C70 - C60 substitution on LUMO is of similar magnitude. A more significant change in HOMO-LUMO energy is seen for the aryl addends. On the other hand, all C70 based molecules have strong visible absorption. For most addends, the crystal structure leads to a stabilization of both LUMO and HOMO by about ~0.2 and ~0.1 eV, respectively, vs single molecules. When using bis-addends, it is also possible to enhance the visible absorption. Explicit consideration of crystal packing with the help of DFTB allowed us to compute electron and hole transport rates, which vary vastly depending on the addends chosen.