Theoretical Study Of Electronic Properties Of Antiaromatic Non-fullerene Acceptors In Organic Solar Cells

Organic solar cells are regarded as a potential photovoltaic technology to convert sunlight into electricity due to their advantages of low-cost,light-weight and easy fabrication.Typically,the active layer of an organic solar cell is bulk- or bilayer-heterojunction consisting of two components,an electron-donating and an electron-accepting material.During the past few decades,fullerene and its derivatives as electron acceptors have played a dominant role in the field of organic solar cells.However,fullerenes suffer from some intrinsic drawbacks,thus hindering futher development of organic solar cells.Recently,organic solar cells based on non-fullerene electron acceptors have achieved high performance due to broad and strong optical absorption and highly tunable electronic levels.To date,the designed and synthesized non-fullerene acceptors are almost all based on aromatic structures,and the A-π-A fused ring acceptors have exhibited the highest power conversion efficiencies.Relative to aromatic systems,anti-aromatics are characteristic of smaller energy gap and larger electron affinity,which is beneficial for broadening optical absorption and increasing electron-accepting ability.Despite of these desirable properties,very few works were reported on the organic solar cells based on “anti-aromatic” electron acceptors.In this contribution,we have systematically assessed the potential of the “anti-aromatic” acceptors in organic solar cells by means of quantum chemical calculations.According to the most successful small molecule acceptors,ITIC and IEIC,we have designed a series of aromatic and antiaromatic A-π-A electron acceptors and investigated their electronic,optical,and charge transport properties by means of(time-dependent) density functional theory.The calculations show that besides the frontier molecular orbitals corresponding to the “aromatic” acceptors,additional occupied and unoccupied frontier orbitals are introduced in the “anti-aromatic” acceptors.Hence,the optical absorption of the A-π-A acceptors is enhanced or broadened upon anti-aromatization.Moreover,our calculations point out the importance of isomerization on tuning the electronic,optical,and electron transport properties of A-π-A electron acceptors.