Design and Synthesis of New Two-Dimensional Non-Fullerene Acceptors for Indoor Light Harvesting

In recent years, organic photovoltaic (OPV) cells have attracted much interest for applications in indoor light harvesting to efficiently convert indoor light into electricity. As a matter of fact, OPV cells already outperform polycrystalline silicon photovoltaic devices in term of power conversion efficiency (PCE) under various indoor light sources largely due to the development of high-performance non-fullerene acceptors to replace previous widely used fullerene derivatives, such as PC₆₁BM and PC₇₁BM. On the other hand, modern inorganic semiconductors based miniaturized electronic devices and sensors are highly efficient and some of them only require a few tens of microwatts of energy to operate. This makes it quite appealing to power them with OPV cells because of the unique features associated with OPVs, such as low cost, light weight, mechanical flexibility, customized shapes and form factors, high throughput production using solution processes, and facile integration with sensors. Recently, our group has designed and synthesized a new series of two-dimensional non-fullerene acceptors based on a rigid electron-deficient benzo[4,5]imidazo[2,1-a]isoindole central core. When blended with a p-type polymer (PM6), one of our non-fullerene acceptors demonstrated a promising PCE of 19.4% and a high V_oc of 0.75 V under an indoor LED illumination of 1300 lux in the PV cells with an active area of 1 cm². For comparison, the well-studied PM6:Y6 bulk heterojunction blend fabricated in our lab gave a V_oc of 0.66 V and a PCE of 17.5% under the same illumination condition. With rational design of side chains and substituents to finely tune the solubility, intermolecular packing, and energy levels of our new non-fullerene acceptors, we believe that their PV performance under indoor light can be further improved, which makes them promising materials for indoor light harvesting to power miniaturized electronic devices and sensors for applications in internet of things (IoT) and smart homes.