Application of Surface Photovoltage Technique to the Determination of Conduction Types of Azo Pigment Films

Abstract

Surface photovoltage spectrum (SPS) and field-induced surface photovoltage spectrum (FISPS) are valuable techniques for the determination of pn conduction type of organic semiconductors. Here, conduction characters of azo pigment films composed of pure 4,4′-2-[N-( -hydroxyl)naphthyl]azodiphenyl (A) and 4,4′-2-{N-[ -hydroxyl-γ-(p-nitroanilino)naphthyl]}azodiphenyl (B) as well as A doped with I 2 vapor (AI 2 ) and B doped with NH 3 gas (BNH 3 ) were explored by means of these techniques. The results of the exploration show that film A has n-type character and film B p-type character. On the basis of the reverse photovoltaic properties, films AI 2 and BNH 3 were judged to be characteristic of p-type and n-type conduction, respectively. It appears that a group rich in electrons, either an electrophobic substituent (naphthanol) at the end side of the azo pigment molecule (A) or a dopant (NH 3 ), bestows the azo pigments with n-type character, whereas an electrophilic group, such as the substituent (p-nitroanilino) connected to azo pigment molecules (B) and I 2 , gives them p-type character. The phenomena are fully discussed based on the energy band modes of the Fermi levels of these materials.

Theoretical and Experimental Study on Exciton Properties of TT-, T-, and H-Nb2O5

“…It is well-known that the SPV signal comes from the change in the surface barrier height caused by surface accumulation of photogenerated carriers under the internal electric field, after the semiconductor is illuminated. Simultaneously, the relationship between the built-in potential V s and N s , V s , can be deduced where e is the electronic charge, N A is the concentration of ionized acceptors, N D is the concentration of donors, N s is the density of surface charge, κ is the dielectric constant, and ε 0 is the permittivity of free space. As a result, the lowest SPV intensity is obtained for A-Nb 2 O 5 .…”

Defect-Induced Yellow Color in Nb-Doped TiO2 and Its Impact on Visible-Light Photocatalysis

“…SPS is a useful technique for detecting the photoinduced charge separation in semiconducting materials Figure d shows that (i) the SPS response decreases as the Nb dopant concentration increases in the UV light region and (ii) the SPS response increases as the Nb dopant concentration increases in the region between 400 and 500 nm.…”

Continuous-Flow Synthesis of the Azo Pigment Yellow 14 Using a Three-Stream Micromixing Process

“…Azo compounds have been used in many fields, such as materials, color photography, painting, biopharmaceutical research, , cosmetics, and ink industries . Due to the expansion of the application fields, the demand for the azo pigments continues to grow.…”