Interfaces analysis by impedance spectroscopy and transient current spectroscopy on semiconducting polymers based metal–insulator–semiconductor capacitors

New insights on traps states in organic semiconductor applying illumination-free transient current method

“…However, dividing the trace current in the three regions requires more attention as one has to consider one crucial effect which could potentially alter the obtained transient current. As shown by previously published impedance measurements, during sputtering of the top contact, Au particles penetrates the semiconductor below and this creates a small less conductive layer close to the contact [13]. In fact, the transit time does not correspond to the first drop of the current but rather to the second drop.…”

“…In fact, the transit time does not correspond to the first drop of the current but rather to the second drop. The existence of the two slopes in the pre-transit region is a direct consequence of the slowing down of charge carriers in the less conductivity region observed close to back contact [13]. Fig.…”

“…We consider a sample with fixed geometrical parameters, across which we apply a voltage step function. The assumed bulk conductivity is set in the range of typical values for P3HT (10 À3 À 10 À6 S/m) [24,13]. The overall input parameters used for the simulations are given in Tables I, II and III.…”

“…Impedance measurements showed that the AC response will include information on band tail states responsible of the dispersion of charge transport mobilities (dispersive transport regime) if the device is biased in accumulation. The AC response will contain additional information on the deep trap states if the device is biased in depletion [9,13]. Fig.…”

“…Though, the latter two methods offer several advantages from the simplicity of the measurements to the wide range of accessible information on the semiconductor properties, they still have their limitations. For IS, the need of complex equivalent circuits for the analysis restrains the accessible information for the band tail characterization [13]. TPC and TOF use a structure with a semiconductor sandwiched between two metal contacts and additionally requires light illumination, a parameter known to be a source of instability due to its potential doping effect on some organic semiconductors [14].…”