Enhanced light-harvesting of benzodithiophene conjugated porphyrin electron donors in organic solar cells

To address the intrinsic issue of conventional porphyrin derivatives with a deficient absorption between Soret and Q bands, we designed and synthesized two porphyrin molecules (BDTP-1 and BDTP-2) bearing a meso-alkyl substituted porphyrin core, benzodithiohene (BDT) ethynylene -bridge and end-capping ethylrhodanine derivatives. Apart from the characteristic Soret and Q bands of porphyrin macrocycle, an extra peak (521 nm for BDTP-1 and 536 nm for BDTP-2) was derived from the BDT units. Using the porphyrin small molecules as electron donors and PC71BM as an electron acceptor, the devices show broad spectral photocurrent generation with a significant contribution from greenlight-harvesting (490-550 nm), resulting in high performances with PCEs up to 7.97%.