Optical and electrical properties of isotype crystalline molecular organic heterojunctions

Abstract

We have studied the electrical and optical characteristics of isotype p‐P organic heterojunctions (HJ) consisting of CuPc (copper phthalocyanine) and PTCDA (3,4,9,10‐perylenetetracarboxylic dianhydride). It is found that the charge‐transport properties of the heterojunction are limited by thermionic emission of holes over the energy barrier at the CuPc/PTCDA heterojunction at low forward and reverse bias, and by series resistance at high voltage. The heterojunction energy barrier at the CuPc/PTCDA valence‐band edge was measured using both current‐voltage and capacitance‐voltage analysis and was found to be ΔE_vC,P=0.48±0.05 eV. Similar measurements made for HJs consisting of CuPc and PTCDA in combination with another perylene‐based material, 3, 4, 9, 10‐perylenetetracarboxylic‐bis‐benzimidazole (PTCBI), suggest that the band offsets for these three materials follow a transitive relationship. That is, ΔE_vC,P=ΔE_vC,B−ΔE_vB,P, where subscripts C, P, and B refer to CuPc, PTCDA, and PTCBI, respectively. The results are discussed in terms of energy‐band and molecular energy‐level models.