Highly Sensitive Organic Photoconductor Using Boron Sub-2,3-naphthalocyanine as a Red-sensitive Film for Stack-type Image Sensors

Abstract

Boron sub-2,3-naphthalocyanine chloride (SubNc) was investigated as a potential red-sensitive organic photoconductive film (OPF). A photoconductive cell was fabricated, and its current–voltage characteristics, both with and without light irradiation, and external quantum efficiency (EQE) were determined. The structure of the photoconductive cell was as follows, with thicknesses in nm given in parentheses: glass substrate/In–Zn–O (100)/spiro-2CBP (30)/SubNc (50)/Alq₃ (30)/Al (50) (spiro-2CBP = 2,7-bis(carbazol-9-yl)-9,9-spirobifluorene; Alq₃ = tris(8-hydroxyquinolinato)aluminum). The spiro-2CBP and Alq₃ layers were inserted between the SubNc layer and the electrodes to block dark current injection. The three organic layers were successively deposited by evaporation in a vacuum on the In–Zn–O-patterned substrate. SubNc film absorbed light in the red region well, with an absorption peak at 695 nm. The EQE of the cell reached 80% when the applied bias was 15 V. In addition, the blocking layers effectively suppressed dark current in the OPF, which corresponded to a current density of 20 nA/cm² at 15 V. These results indicate that SubNc is a promising candidate as a red-sensitive OPF.