Suppressed Non-Radiative Loss and Efficient Hole Transfer at Small Highest Occupied Molecular Orbital Offset Enables 19.73% Efficiency Binary Organic Solar Cells with Small Efficiency-Cost Gap

Suppressing energy/voltage loss and realizing efficient charge transfer at small frontier molecular orbital offsets between donor and acceptor is viable to simultaneously improve open-circuit voltage (Voc) and short-circuit current (Jsc), and thus power conversion efficiency (PCE) of organic solar cells (OSCs). Here, two A-DA’D-A type acceptors, PEH-F and TEH-F, are designed and synthesized with different conjugated outer side chains, to pursue high-efficiency and cost-effective OSCs for industrialization. In comparison with TEH-F (thienyl outer side chain), PEH-F with phenyl outer side chains delivers up-shifted frontier energy levels, wider optical bandgap, and higher absorption coefficient. By adopting low-cost polymer PTQ11 as donor, the PEH-F-based device realizes low energy loss of 0.511 eV with suppressed non-radiative loss of only 0.182 eV, and exhibits efficient exciton dissociation and hole transfer even at an extremely small highest occupied molecular orbital offset of 0.06 eV. Eventually, the PTQ11:PEH-F-based binary device demonstrates a superior PCE of 19.73 % with high Voc and Jsc simultaneously, which is the highest PCE to date for OSCs based on low-cost polymer donors. More importantly, this device shows small efficiency-cost gap for industrialization with the estimated minimum sustainable price (MSP) of 0.35 $ Wp-1, which is dramatically lower than other reported high-performance OSCs.