Figure 2(a) present theincreasing of the current density by the built-in the applied voltage and athigher voltages the J-V curve is determined by trap-space-charge limitedmobility and the resistance of the contacts.
Since different slope can be foundat different points yielding different transition phase of organicsemiconductors. When comparing the J-Vcharacteristics for the various temperatures 114K, 145K, 155K, 218K, 247K, 275Kand 296K, transition points are identified with the built-in temperature whereit is up to 217K and the applied voltage is 0.7V. Inorder to confirm our results, we report in figure 2(b) the current densityvoltage characteristic for the same device at 296K and for two cases ofdisorder energy 30meV and 60meV which are presented the transition phase of theC60 which is transformed from cube centre face to simple cube.
Clearly, theagreement between the results extract from literature and simulations is fairlywell when the disorder energy is 30meV, however for the case of 60meV, there isa huge gap. Indeed, Coulomb interactionsreduce the charge trapping, but also induce an additional energetic disorder.When is smallerthan 1, the disorder induced by Coulomb interaction is not completely screenedout by the intrinsic disorder of the material. However, when is larger than 2, the disorder induced by Coulombinteraction is completely screened out by the intrinsic disorder of thematerial; the number of intrinsic low-energy states is large, and the barrierreduction effect due to Coulomb interactions can be important, leading to anincrease in the charge carrier mobility with density.
Indeed, chargeinjection strongly depends on the energy level matching between the Fermi levelof the metal electrodes and organic semiconductors energy levels, lowunoccupied molecular orbital (LUMO) and highest occupied molecular orbital(HOMO). In this context, we have studied the effect of contact metal on thecurrent density and the charge carrier mobility of the active layer (SubPc/C60) which is sandwichedbetween the two metal electrodes. We have used PEDOT:PSS and BCP hole andelectron electrodes, respectively. These materials are employed to inject one type of charge carriers intothe semiconductor layer seen figure 3.