Fig. 3: General trend of the dark current densities of OPDs.

a, Experimentally determined J_D measured at −0.1 V as a function of E_CT of the OPDs studied in this work (triangles, square and circles) and a large set of narrow-gap BHJ systems from the literature (stars¹⁶). The inset shows the J_D–V characteristics of PBDB-T:EH-IDTBR, demonstrating the superposition of shunt (linear) and diode current (m = 2) components as well as the dominance of shunt in the reverse bias of systems with wide D–A gaps (E_CT > 1.2 eV). b, Extracted dark saturation current density as a function of E_CT of the OPDs studied in this work (triangles, square and circles), as well as those derived from literature values with E_CT < 1.2 eV (stars). Red lines represent the expected trend, \({J_0} = {J_{00}\exp \left( { - \frac{{E_{{{{\mathrm{CT}}}}}}}{{2kT}}} \right)}\), when mid-gap trap-mediated transitions (E_a = E_CT/2) dominate the dark current. Here, the red solid line corresponds to a J₀ with prefactor J₀₀ = 2,000 A cm⁻². For comparison, we have included a shaded area with an upper bound corresponding to J₀₀ = 2 × 10⁵ A cm⁻² and lower bound corresponding to J₀₀ = 20 A cm⁻².