SCLC Measurements in Nickel Phthalocyanine Thin Films

Abstract

Sandwich structures of Au/NiPc/Au were fabricated by sequential vacuum thermal sublimation onto borosilicate glass substrates. dc electrical measurements were performed for several NiPc thin films of different thickness in the range (d 0:25±1.09 mm). The relative permittivity was measured at a low frequency of 100 Hz, yielding a value of e r 2:74. This value is considerably lower in comparison with previously published data for various phthalocyanine materials. Current density±voltage characteristics at room temperature reveal an Ohmic conduction in the lower voltage range, followed by SCLC in the higher range, where the latter was found to be controlled by an exponential trap distribution. The plot of current density versus thickness provides further evidence of this effect. The results are analyzed in terms of exponential trap distribution yielding the following values: The temperature parameter characterizing the exponential trap distribution T t 1165 K, the concentration of thermally generated holes p 0 1:40 Â 10 16 m ± ±3 , trap concentration per unit energy range P 0 4:71 Â 10 43 J ± ±1 m ± ±3 and total concentration of traps N t e 7:57 Â 10 23 m ± ±3 .

Alternating current conduction properties of thermally evaporated α-nickel phthalocyanine thin films: Effects of oxygen doping and thermal annealing

“…͑3͒, 0 is the permittivity of the semiconductor (ϳ2.42ϫ10 Ϫ11 F m Ϫ1 for NiPc͒, 5 R is the separation between the neighboring sites, and W the hopping barrier potential after lowering of the effective barrier (W m ) due to Coulomb wells overlap. By substituting Eq.…”

“…Gold was chosen because it is known to provide good and reproducible ohmic contacts with many phthalocyanines including NiPc. 4,5 Details of the fabrication method employed have been reported earlier. 9 The active conduction area of each device ͑A͒ was measured after fabrication to be approximately 1.2ϫ10 Ϫ5 m 2 .…”

“…Contact effects between Au and ␣-NiPc are also excluded since electrical conduction through similar devices has been shown to be a bulk rather than an electrode limited process. 5 …”

Oxygen induced p-doping of α-nickel phthalocyanine vacuum sublimed films: Implication for its use in organic photovoltaics

“…For measurement of dark conductivity of the as evaporated and oxygen doped NiPc films, gold ohmic contacts are employed. 12 In the case of Schottky devices, Pb as the low work function cathode is used. 9 The I -V characteristics for freshly prepared devices are measured in situ.…”

“…This behavior is characteristic for space-chargelimited conduction ͑SCLC͒ governed by exponentially distributed trapping levels. 14,12 In this regime J is described by…”