Dithienoquinoxalineimide-Based Polymer Donor Enables All-Polymer Solar Cells Over 19% Efficiency

All-polymer solar cells (all-PSCs) have been regarded as one of the most promising candidates for commercial applications owing to their outstanding advantages such as mechanical flexibility, light weight and stable film morphology. However, compared to large amount of new-emerging excellent polymer acceptors, the development of high-performance polymer donor lags behind. Herein, a new D-pi-A type polymer donor, namely QQ1, was developed based on dithienoquinoxalineimide (DTQI) as the A unit, benzodithiophene with thiophene-conjugated side chains (BDTT) as the D unit, and alkyl-thiophene as the pi-bridge, respectively. QQ1 not only possesses a strong dipole moment, but also shows a wide band gap of 1.80eV and a deep HOMO energy level of -5.47eV, even without halogen substituents that are commonly indispensable for high-performance polymer donors. When blended with a classic polymer acceptor PY-IT, the QQ1-based all-PSC delivers an outstanding PCE of 18.81%. After the introduction of F-BTA3 as the third component, a record PCE of 19.20% was obtained, the highest value reported so far for all-PSCs. The impressive photovoltaic performance originates from broad absorption range, reduced energy loss, and compact pi-pi stacking. These results provide new insight in the rational design of novel nonhalogenated polymer donors for further development of all-PSCs.