Suppressed non-radiative loss and efficient hole transfer at a small highest occupied molecular orbital offset endows binary organic solar cells with 19.73% efficiency and a small efficiency-cost gap

Abstract

Suppressing energy/voltage loss and realizing efficient charge transfer at small frontier molecular orbital offsets between the donor and acceptor is viable to simultaneously improve the open-circuit voltage (V_oc) and short-circuit current (J_sc), and thus the 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, a wider optical bandgap, and a higher absorption coefficient. By adopting low-cost polymer PTQ11 as a donor, the PEH-F-based device realizes a low energy loss of 0.511 eV with a 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 V_oc and J_sc simultaneously, which is the highest PCE to date for OSCs based on low-cost polymer donors. More importantly, this device shows a small efficiency-cost gap for industrialization with the estimated minimum sustainable price (MSP) of 0.35 $ per W_p, which is dramatically lower than those of other reported high-performance OSCs.