**4. Conclusion**

We have reported in this work a theoretical investigation on a D-A type copolymer and a D-π-A-π-D type small molecule based on CPDT derivatives as electron donor with BT or DPP as electron acceptor moiety.

The studied materials exhibited narrow band-gap energies with high planar structures governed by intra-molecular non-covalent interactions. The particular conjugated arrangement added to the dicyanomethylene Bridge groups has leaded to considerable intra-molecular charge transfer (ICT) within these molecules. The optical absorption spectra covered an interesting part of the solar spectrum which indicated that the studied molecules exhibit high light harvesting efficiency. The deep HOMO energy levels of these molecule encourage their application as donor materials in a BHJ-OSCs with the [70] PCBM as acceptor. The TDM analysis showed the ease dissociation of excitons within the considered materials at the first exited state that leads to enhance the photovoltaic properties. The PCEs, estimated using Scharber diagram, close to 10% were reached.

This study revealed that the reliability of the designed donor materials for developing efficient materials for BHJ OSCs. A molecular tuning based on these designed conjugated materials may enhance the donor materials efficiency in photovoltaic applications.
