Reduced leakage current and improved performance of an organic photodetector using an ytterbium cathode interlayer

Abstract

We report the electron transport and hole-blocking properties of ytterbium, which make it suitable for use as the cathode interlayer for the poly(3-hexylthiophene-2,5-diyl) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction in organic photodetectors (OPDs). The final device structure consisting of ITO/NiOx/P3HT:PC₆₀BM/Yb/Al is compared to devices with Ca as the cathode interlayer and without a cathode interlayer. The performance of OPDs is analyzed, and effective carrier extraction and hole blocking are confirmed through the dynamic characteristics of the devices. The use of a Yb layer in the OPDs improves the resistance, thereby improving the carrier extraction and decreasing the leakage current significantly. A figure of merit for the dynamic characteristics, namely the bandwidth of Yb, is improved owing to the fast response time. The bandwidth exceeds 100 kHz at a relatively low light intensity. Optical–electrical measurements are performed, and J–V characteristics, impedance, and dynamic characteristics are analyzed. We investigate the effects of the Yb layer on the performance of the OPDs, focusing on its carrier extraction, leakage current, and resistance components.