New insights into DPP3Th and C70 based planar solar cells: a study combining DFT and experimental approach

Abstract In this work, small molecule-based solar cells were produced with a solution-processed diketopyrrolopyrrole-terthiophene (DPP3Th) as electron donor material and thermally evaporated fullerene (C70) film as acceptor material. The DPP3Th molecule was synthesized by the Suzuki cross-coupling reaction, resulting in energy values of the Highest Occupied Molecular Orbital (HOMO) equal to -5.30 eV, Lowest Unoccupied Molecular Orbital (LUMO) equal to -3.80 eV and optical band gap (Eg) of 1.60 eV. Theoretical simulation pointed out a limited torsional movement between the DPP and thiophene units, which contribute to shift the absorption edge of the DPP3Th to higher wavelengths and thus, resulting in extended photon collection. The DPP3Th and C70 molecules present complementary absorbance spectra (from 300 nm up to ca. 725 nm). Moreover, the DPP3Th/C70 interface provides a favorable energy barrier to electron transfer from the donor to the acceptor, resulting in open circuit voltage (Voc) of 0.72 V which is a promising step toward application in solar cells.