Fig. 4: Design rules to improve the V_OC in TOSCs.

a, Schematic illustration of the morphologic effect of the guest component on the host binary blends in TOSCs. b,c, Strategies to improve the V_OC in Case-1 TOSCs: the changes on the V_OC^rad should be minimized, and the improved V_OC can be reached by reducing the ΔV_nr (b); under the thermal equilibrium (described by the black arrows), reduced ΔV_nr can be realized by exploiting the thermal population of the more emissive states related with the guest component, where the luminescent efficiencies of different states are represented by the thickness of the coloured arrows (c). From the perspective of the device performance, the guest binary device should have higher EQE_EL than the host binary device (that is, EQE_EL^G > EQE_EL^H). In addition, to fully make use of the CT_G and LE_G without sacrificing the V_OC^rad, the CT_G energy should be close to the CT_H energy (that is, \({E}_{{{\rm{CT}}}_{{\rm{H}}}}\cong{E}_{{{\rm{CT}}}_{{\rm{G}}}}\)). d,e, Strategies to improve the V_OC in Case-2 TOSCs: the improved V_OC can result from both increased V_OC^rad and reduced ΔV_nr (d); the guest component suppresses the aggregation of the host binary blends, leading to increased LE_H and CT_H energies and thus increased V_OC^rad (e). In addition, suppressed aggregation of the host binary blend also reduces the ACQ effect, enhancing the luminescent efficiencies of both LE_H and CT_H and thus reducing the ΔV_nr. Black arrows in e describe the thermal equilibrium condition; the thickness of the coloured arrows represents the luminescent efficiencies of different states; the dashed lines represent the initial conditions of the host binary blend; and the solid lines represent the conditions of the host binary blend after adding the guest component.