Effect of annealing temperatures on the turn-on voltage of organic Schottky diode based on DPP(BTFu)2

The electrical properties of diketopyrrolopyrrole ethyl-hexylated (DPP(TBFu)2) thin film sandwich structure of the ITO/DPP(TBFu)2/Al configuration for different annealing temperatures ranging from 40 to 130°C is investigated. The current–voltage characteristics showed an excellent rectifying behaviour of the device, and from which the diode parameters were extracted. It is found that all parameters remain constant upon annealing temperatures, with the exception of the turn-on voltage. An increase of the turn-on voltage from an initial value of 1.6–2.08 V is noticed starting from 70 to 100°C, respectively. This fact is attributed to the effect of residual solvent induced defect states that may act as free carriers. Defect states density for the non-annealed and annealed device at 130°C derived from capacitance–voltage measurements is found to correlate well with the turn-on voltage. It is found that annealing the device at 130°C results in a smaller concentration of defect states. In addition, it is also found that the annealing process produces the flat band voltage drop, which has a direct impact on the turn-on voltage.