| 초록 |
We synthesized four acceptor-donor-acceptor type small-molecules of Si1TDPP-EE,EO,OE and OO. Molecular backbones consist of dithienosiloe (Si) as donor and diketopyrrolopyrrole (DPP) as acceptor to have both optimal energy levels for exciton separation and planarity for close molecular packing and high carrier transport. Moreover, molecular crystal orientations were controlled by employing a combination of side alkyl chains of 2-ethyl hexyl(E) or n-octyl(O). All the molecules showed a low band gap around 1.60 eV. X-ray diffraction patterns indicated that Si1TDPP-EE and Si1TDPP-EO are mostly edge-on, whereas Si1TDPP-OE and Si1TDPP-OO are face on. We found this crystal oriention affected the photovoltaic performance significantly. This result demonstrates that an appropriate position of alkyl chains make a dramatic change in crystallinity, crystal orientation, and thus photovoltaic performance. |
