Trap-free space-charge-limited electron transport in amorphous tin(IV) phthalocyanine dichloride thin film

Abstract

The morphology and electrical properties of thin films of an n-type organic semiconductor tin(IV) phthalocyanine dichloride (SnCl2Pc) are investigated. An investigation of atomic force microscopy and x-ray diffraction shows that the vacuum-deposited SnCl2Pc films on room-temperature glass substrates exhibit a homogeneous amorphous state. The temperature-dependent current–voltage characteristics of the electron-only devices show that the electron transport in SnCl2Pc thin films is bulk-limited, from the Ohmic region (J ∼ V) at low voltages to the trap-free space-charge-limited current (TFSCLC) region (J ∼ V2) at high voltages. The linear dependence of current on voltage at low voltages yields the temperature-dependent conductivity, while the TFSCLC relationship provides a direct measurement of the free-electron mobility as a function of electric field and temperature. The zero-field electron mobility at 293 K is as high as (1.8 ± 0.3) × 10−4 cm2 V−1 s−1. It can be seen that the obtained mobility and conductivity obey well the Gaussian disorder model and the three-dimensional variable range hopping model, respectively.