Efficient Quaternary Organic Solar Cells with Parallel-Alloy Morphology

Two compatible donors (PBDB-T and PTB7-Th) and two miscible acceptors (ITIC and FOIC) are employed to deliver a parallel-alloy morphology model in non-fullerene-based quaternary organic solar cells. PBDB-T and PTB7-Th form a parallel link with a slight adjustment of molecular packing into enhanced face-on crystallites while ITIC disperses into discontinuous FOIC microcrystal regions to form continuous and ordered alloy-like acceptor phases. Characterization of blend morphology highlights the parallel-alloy model-enabled by the introduction of PBDB-T and ITIC, which contributes to improved molecular packing and reduced domain size resulting in efficient charge generation and consistent transport channels. This successful parallel-alloy quaternary blend morphology demonstrates an enhanced optical absorption, optimized domain size, and nanostructures toward simultaneous improvement in charge transfer and transport. Therefore, a power conversion efficiency of 12.52% is realized for a quaternary device which is 6% higher than the ternary device (PBDB-T:PTB7-Th:FOIC) and 12% higher than the binary device (PTB7-Th:FOIC). Domination of quaternary devices over ternary and binary blends, which is another feasible way to realize highly efficient devices through further investigation of quaternary OSCs, is presented.