Tandem organic solar cells with 18.67% efficiency via careful subcell design and selection

Abstract

The use of tandem structures is an efficient way to simultaneously tackle the absorption and thermalization losses of single junction solar cells and the subcell active layer design and selection always play a crucial role in the construction of tandem organic solar cells. In this work, a wide bandgap acceptor F-ThBr with the fluorene core and brominated thiophene-fused end group has been designed. The device based on D18:F-ThBr offers a PCE of 13.02% with a high V_oc of 1.089 V, a J_sc of 16.68 mA cm⁻² and a FF of 71.69%, which makes it a good candidate as a front cell for the construction of tandem OSCs. Meanwhile, in view of the complimentary absorption with F-ThBr and high V_oc, PM6:CH1007:PC₇₁BM is selected and optimized as the rear cell. Using the above subcells, a solution-processed tandem OSC is constructed and demonstrates a power conversion efficiency of 18.67%.