Organic bulk heterojunction photodetectors based on polymer blends with unbalanced mobilities (Conference Presentation)

Abstract

We investigate bulk heterojunction organic photodetectors with unbalanced charge carrier mobilities in the active layer. We present an experimental example of an organic photodetector with external quantum efficiency exceeding 75% (at illumination 638 nm), and bandwidth over 1 MHz, utilizing a 50 nm thick active layer with electron mobility ≈ 10−4 −10−3 cm2/(Vs) and low hole mobility ≈ 5 × 10−7 cm2/(Vs). The presented drift-diffusion simulation of bulk heterojunction photodiodes with Langevin recombination indicates that the bandwidth of photodiode is approximately independent of the mobility of slower charge carriers in the blend. The negative effect of low mobility on the responsivity can be compensated by increasing the reverse bias. Our study shows that well performing organic photodetectors can be fabricated using organic semiconductors having too low mobility for photovoltaic applications. Moreover, when optimizing the bandwidth of bulk heterojunction photodetectors, attention should be focused on the semiconductor with higher mobility.