18.2%-efficient ternary all-polymer organic solar cells with improved stability enabled by a chlorinated guest polymer acceptor

Although the polymer/polymer blend systems still lag far behind small-molecule-acceptor-based counterparts in power conversion efficiencies (PCEs), the ternary blending strategy provides a simple and promising avenue to achieve an ideal nanoscale blend morphology for reducing the efficiency-stability gap of all-polymer solar cells (all-PSCs). Herein, we designed a narrow-band-gap chlorinated polymer acceptor PY-2Cl and incorporated into the PM6:PY-1S1Se host blend. The addition of PY-2Cl extends the absorption spectra, improves the molecular packing of host-guest acceptors, solidifies the blend microstructure, and suppresses the non-radiative recombination. Consequently, the PCE of the ternary blend is improved up to 18.2% (certified value 17.8%), which represents the highest PCE reported for all-PSCs so far. Impressively, the ternary blend exhibited smaller Urbach energy and better operation stability than did the corresponding binary systems. This work heralds a brighter future for accelerating the development of high-performance all-polymer systems by molecular design and ternary strategy.