Design, Synthesis And Application Of Novel Donor Materials For Small Molecule Organic Solar Cells

The organic solar cells are gradually becoming a new and important aspect of development in solar cells. Based on the molecular weight, organic solar cells can be divided into polymer solar cells (PSCs) and small molecule organic solar cells (SMOSCs). Compared with PSCs, though the efficiency is a little lower, SMOSCs are still of great interest to the research community due to the distinct advantages of small-molecule semiconductors, such as well-defined structures, easier synthesis and batch-to-batch stability. The research on novel and efficient donor materials is always one of the core research fields in SMOSCs in recent years.A D-π-A type small molecule PTZ1 and an A-π-D-π-A type small molecule PTZ2 with phenothiazine as the central building block and dicyanovinyl as the electron-withdrawing end-group have been designed and synthesized. Compared with D-π-A type donor material PTZ1, the donor material PTZ2 with A-π-D-π-A configuration shows better response to solar light. When becoming solid film, PTZ2 also displays better molecular packing. Inverted bulk heteroj unction (BHJ) solar cells were made by using PTZ1/PTZ2 as donor materials and PC71BM as acceptor materials. Both PTZ1- and PTZ2-based solar cells possess high VOC.An improved efficiency of 3.25% was obtained for the PTZ2-based solar cells.On the basis of previous research, a D-π-A type small molecule POZ4 and a A-π-D-π-A type small molecule POZ6, in which phenoxazine was used as the central building block and dicyanovinyl was employed as the electron-withdrawing end-group, have been designed and synthesized. Compared with PTZ1 and PTZ2, the maximum absorption peaks of both POZ4 and POZ6 show obvious red shift in ultraviolet visible absorption spectrum. And the thermal stability of both POZ4 and POZ6 has been improved. Normal BHJ solar cells were made by using POZ4/POZ6 as donor materials and PC71BM as acceptor materials. The active layers were annealed at 90℃ for 15 min. The conversion efficiency of POZ4-and POZ6-based solar cells reaches 3.58% and 5.6% respectively. The device fabricated with POZ6:PC71BM (1:1) shows a much better balanced hole and electron mobility of 2.24×10-4 cm2·V-1·s-1 and 3.17×10-4 cm2·V-1·s-1, respectively.