New Conjugated Polymers Based on Dithieno[2,3‐e:3′,2′‐g]Isoindole‐7,9(8H)‐Dione Derivatives for Applications in Nonfullerene Polymer Solar Cells

Abstract

The fast evolution of the narrow bandgap nonfullerene acceptors requires new conjugated wide bandgap polymers for the use of nonfullerene polymer solar cells (PSCs). Herein, two new wide bandgap A1–D1–A2–D1 conjugated polymers with the same dithieno[2,3‐e:3′,2′‐g]isoindole‐7,9(8H)‐dione (DTID) acceptor (A1) and thiophene donor (D1) and different A2 acceptor units, i.e., benzothiadiazole (BT) and fluorinated benzothiadiazole (f‐BT) denoted as P113 and P114, are designed, and the effect of fluorination of the BT acceptor unit on the photovoltaic properties of PSCs using nonfullerene acceptors is investigated. It is found that the incorporation of fluorine atom into the BT acceptor unit increases the absorption coefficients and the relative dielectric constant. The increase in photoluminescence quenching, reduction in charge recombination loss, and improvement in the charge carrier life are observed for P114. All these factors result in the drastically improved power conversion efficiency of P114:ITIC‐m‐based PSC to 10.42% with a small energy loss of 0.56 eV as compared with the P113 counterpart (8.74% with an energy loss of 0.69 eV) under identical conditions. The low energy loss is beneficial to overcome the trade‐off between open‐circuit voltage and short‐circuit current.