Novel donor–acceptor molecules as donors for bulk heterojunction solar cells

Three novel donor–acceptor molecules (BCPD, BPPD and PDHC) have been investigated as donors for the bulk heterojunction solar cells. BCPD and BPPD have the same acceptor group of TPO while BCPD and PDHC have the similar donor group of carbazole. The absorption data indicates that the introduction of either strong electron-donating group or strong electron-withdrawing group will induce the red shift of ICT transition absorption. Electrochemistry measurement shows that the three compounds present reversible or partly reversible oxidation and reduction processes. When the donor moiety was changed from carbazole to phenothiazine, the oxidation potentials shifted from 1.10 V to 0.72 V. While the acceptor moiety was changed from TPO to CEM, the reduction potentials shifted from −1.42 V to −0.92 V. The bulk heterojunction solar cells using the three compounds as donors and PCBM as acceptor were fabricated. The cell based on PDHC containing strong electron-accepting group shows a relatively high energy conversion efficiency of 0.51% under the illumination of white light at 100 mW cm−2, which is almost two times of the magnitude of the cells based on BCPD and BPPD.