Research of carrier mobility in NPD through negative differential susceptance spectra

In this paper, the hole carrier mobility of organic semiconductor N,N' -diphenyl-N,N' bis(1,1'- biphenyl)-4,4'-diamine (NPD) was researched by negative differential susceptance spectra (-ΔB = -w(C - Cgeo) ∼ f). Under the condition of space charge limited current (SCLC), through solving the drift current equation and Poisson equation and simulating the spectra -ΔB = -w(C - Cgeo) ∼ f, the relationship between the peak of -ΔB = -w(C - Cgeo) ∼ f spectra ( 1 fp = τp) and the transfer time of carrier (τdc) could be achieved to be τdc = k×τp. So the hole-only device of ITO/NPD/Ag was fabricated to determine the capacitance spectra, and through which its -ΔB = -w(C -Cgeo) ∼ f could be plotted. According to the relationship of τdc = k × τp, where k was determined to be 0.56, the transfer time and further the carrier mobility could be obtained. The carrier mobility depended on the electric field according to Poole-Frenkel model was further investigated in this report.