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

摘要

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 (lambda(h)), as compared to electron mobility (lambda(e)), 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 -2.36eV), with strong absorption in UV-Visible region in the range of 459nm to 500nm 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 (V-oc) of 3.01eV (with respect to HOMOdonor-LUMOPC61BM) was shown by M3. The open circuit voltages (V-oc) of R, M1, M2 and M3 were 2.91eV, 3.01eV, 2.77eV and 3.02eV, respectively.