(712a) High Charge Transfer and Charge Separation Donor-Electret-Acceptor Framework for Solar Cell Applications

Solar cells try to mimic the natural process of photosynthesis to convert the light energy into electrical energy. Long-range electron transfers occur rapidly over 10 Å distances between donor-acceptor pairs within the protein matrix. However, protein based moieties are not suited for the electronic applications. Widely employed Donor-(Bridge)_n-Acceptor (DB_nA; n≥1) framework typically fails to effectively transfer the charge over longer distances leading to larger exciton binding energies and lower power conversion efficiencies in organic solar cells. Modifying the dipole neutral bridge into an electret we propose a Donor-Electret_n-Acceptor (DE_nA; n≥1) model which addresses the limitations of conventional DBA architecture. (1) DEAs offer higher charge transfer (CT) and charge separation (CS) which overcomes the inherent length dependecy of DBAs with increasing chain length. (2) CS over ~12 Å and beyond is possible with the proposed DEA architecture which can compete with natural protein helix in efficient electron transfer and exciton dissociation. (3) Electret allows to tune the ground state (GS) dipole without comprimising on higher CT and CS properties; lower GS dipole enables the solubitliy of DEAs in milder solvents. (4) Higher degrees of freedom in the substitution patterns provided by the electret allows not only to alter CT and CS but also other electronic and optical properties like HOMO-LUMO gaps, optical gaps, dipoles, oscillator strengths etc. (5) Opens a new window in exploiting the substitution patterns provided by the electret to design novel materials which have potential applications in diverse areas. Our DFT/TD-DFT studies employing optimally tuned range separated hybrids predict accurate optical properties against the experimental results.