Narrow band green organic photodiodes for imaging

Accurate color reproduction using image sensors requires four narrow-band absorbing photodetectors (blue, green, yellow and red). Current photodetectors use a broadband photodetector in combination with color filters, which generally do not have sufficient wavelength discrimination for illuminant independent color recognition. We have developed a green-sensitive organic photodetector, in which color selection is achieved using a narrow-absorbing ketocyanine chromophore, coupled with a low finesse electro-optical cavity inducing further spectral narrowing. The optimized device contained a bulk heterojunction light-absorbing layer comprised of a ketocyanine dye blended with 6,6]-phenyl-C₆₁-butyric acid methyl ester. The photodetector had a response full width at half maximum of 80 nm centered around 525 nm, and an external quantum efficiency of 15% at −1.0 V, which is the highest so far reported for a narrow band green-absorbing organic photodetector. The performance of this detector is sufficient to meet the specifications required by machine vision systems.