Designing dithienothiophene (DTT)-based donor materials with efficient photovoltaic parameters for organic solar cells.

Three acceptor-donor-acceptor (A-D-A)-type small donor molecules (M1, M2 and M3) were evaluated for optoelectronic properties through density functional theory calculations. These designed molecules consist of a dithieno [2,3-b:3,2-d] thiophene (DTT) donor group linked with 2-(3-methyl-4-oxothiazolidin-2-ylidine)malononitrile acceptor through three different bridge groups. The effect of the donor and three different bridge spacer groups on the designed molecules for opto-electronic properties was evaluated in comparison with the reference molecule R. The reorganization energies of the designed donor molecules suggest very good charge mobility property. The lower value of hole mobility (λh), as compared to electron mobility (λe), revealed that the three designed molecules are best for hole mobility. Frontier molecular orbital (FMO) surfaces confirm the transfer of charge from donor to acceptor unit during excitation. The designed molecules show relatively low HOMO values (in the range of -2.19 to -2.36 eV), with strong absorption in UV-Visible region in the range of 459 nm to 500 nm in chloroform solvent. Electron-hole binding energy results indicate that the designed molecule M2 contains the highest amount of charge, which may dissociate into separate charge easily. Among all the studied molecules, the highest open circuit voltage (Voc) of 3.01 eV (with respect to HOMOdonor-LUMOPC61BM) was shown by M3. The open circuit voltages (Voc) of R, M1, M2 and M3 were 2.91 eV, 3.01 eV, 2.77 eV and 3.02 eV, respectively. Graphical abstract Three newly acceptor donor acceptor (A-D-A)-based donor small molecules (M1, M2 and M3) were designed by taking dithieno [2,3-b:3,2-d]thiophene (DTT) as a donor group linked with acceptor 2-(3-methyl-4-oxothiazolidin-2-ylidine)malononitrile through three different bridge groups. All the designed molecule were compared with the well-known reference compound R. Optical properties, electronic properties, photophysical and excited state energy were calculated and compared with the well-known, and recently published, reference molecule R . All the newly designed molecules shows good optoelectronic properties with respect to R.