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 ∼ V 2) 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.

Ambipolarity and Dimensionality of Charge Transport in Crystalline Group 14 Phthalocyanines: A Computational Study

“…The chosen amplitude σ ε = 2 k B T = 51.4 meV is typical of mild disorder conditions, in line with experimental data. For instance, Qiao and co-workers reported values of about 90 meV for amorphous thin films of compound 2 …”

“…To gain further insight into the impact of energetic disorder on mobility values and on the anisotropy of transport properties, hole and electron mobilities were computed in the three crystallographic planes of compound 1 , using an applied electric field of 1 × 10 6 V/cm, typical of time-of-flight experiments . Mobility values along the three crystal axes are reported in Table , together with the dimensionality Δ of charge transport, arbitrarily defined as follows: (i) 1D mobility, μ i /μ j ≥ 3 and μ i /μ k ≥ 3; (ii) 2D, μ i /μ j < 3 and μ i /μ k ≥ 3; and (iii) 3D, μ i /μ j < 3 and μ i /μ k < 3, where i , j , and k correspond to the crystallographic directions with μ i > μ j > μ k .…”

“…For instance, Qiao and co-workers reported values of about 90 meV for amorphous thin films of compound 2. 48 3. Dynamic diagonal disorder (ε D ): site energies are reinitialized at each hopping event, using a Gaussian distribution with standard deviation σ ε = 2k B T, describing fluctuations occurring on time scales that are smaller than the charge hopping time.…”

Solution processed transparent anatase TiO2 nanoparticles/MoO3 nanostructures heterojunction: high performance self-powered UV detector for low-power and low-light applications

“…The value of the exponent is slightly greater than 2 and this suggests that the injected carriers have just entered into the space charge region. 59 I-V characteristics measured under UV light illumination (352 nm) clearly showed the photoconductive nature of the devices. The photocurrent (the difference between the current under UV illumination and dark) of the bilayer device was observed as 1.94 mA at 0 V and it reached a value of 840 mA at a reverse bias of À1 V. The photocurrent without bias was 40 times higher and with bias, it was 3 times higher when compared to that of the single layer TiO 2 nanoparticle based device for which the photocurrent was only 42 nA at 0 V and 228 mA at À1 V (Fig.…”

“…The value of the exponent is slightly greater than 2 and this suggests that the injected carriers have just entered into the space charge region. 59 …”