The energy density formula illuminated that widening the voltage window and maximizing capacitance are effective strategies to boost the energy density of supercapacitors. However, aqueous electrolyte-based devices generally afford a voltage window less than 1.2 V in view of water electrolysis, and chemically converted graphene yields mediocre capacitance. Herein, multielectron redox-reversible, structurally stable indanthrone (IDT) π-backbones were rationally coupled with the reduced graphene oxide (rGO) framework to form IDT@rGO molecular heterojunctions. Such conductive agent-and binder-free film electrodes delivered a maximized capacitance of up to 345 F g −1 in a potential range of −0.2 to 1.0 V. The partner film electrode−Ti 3 C 2 T x MXene which worked in the negative potential range of −0.1 to −0.6 V− afforded a capacitance as large as 769 F g −1 . Thanks to the perfect complementary potentials of the IDT@rGO heterojunction positive electrode and Ti 3 C 2 T x MXene negative partner, the polyvinyl alcohol/H 2 SO 4 hydrogel electrolyte-based flexible asymmetric supercapacitor delivered an enlarged voltage window of 1.6 V and an impressive energy density of 17 W h kg −1 at a high power density of 8 kW kg −1 , plus remarkable rate capability and cycling life (capacitance retention of ∼90% after 10000 cycles) as well as exceptional flexibility and bendability.

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