Nanosecond response organic photodiodes: From device physics towards biosensor applications
- PDF / 1,216,030 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 34 Downloads / 228 Views
Nanosecond response organic photodiodes: From device physics towards biosensor applications S. Valouch, S. W. Kettlitz, N. Christ, S. Züfle, C. M. Ögün, M. Nintz and U. Lemmer Karlsruhe Institute of Technology, Light Technology Institute, Engesserstr. 13, 76131 Karlsruhe, Germany ABSTRACT In this work we investigate polymer photodiodes based on a blend system consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and the fullerene derivative (6,6)-phenyl C-butyric acid methyl ester (PCBM). An optimized low source impedance architecture allows measurements in the GHz range with minimum distortion, while at the same time allowing to probe the favourable sandwich device structure. We have studied the underlying device physics and investigated the influence of parameters such as active layer thickness and bias voltage on the transient photocurrent response. Using a numerical simulation software combining a self-consistent driftdiffusion model in conjunction with an optical model based on the transfer matrix method we model the transient photocurrent of polymer photodiodes. Transient photocurrent measurements utilizing this low impedance device architecture excited by 1.6 ns short laser pulses show very good correlation between simulated and measured results. Furthermore we have developed an encapsulation technique to integrate high-speed organic photodiodes onto standard printed circuit boards (PCBs) to avoid the degradation of the devices by humidity or oxygen. INTRODUCTION Photodiodes fabricated from organic semiconductors have the potential to provide cost effective optical detection and easy integration in biological sensing applications [1]. The application of fast organic photodiodes based on P3HT/PCBM [2] for sensing [3] and data communication applications [4] has been demonstrated, underlining the capability for fast signal detection. In many biosensing applications, the speed of detection is of utmost importance, among the most demanding applications being flow cytometry [5] and fluorescence lifetime measurements [4], where response times in the submicroseconds are required. Here, we aim to understand the underlying device physics in high speed organic photodiodes via numerical simulation, to develop new ways for encapsulation and integration and to optimize them for sensor applications. EXPERIMENT Organic photodiode fabrication Devices are fabricated on glass substrates covered with an indium-tin-oxide (ITO) layer as transparent electrode (thickness: 130 nm). Substrates are cleaned by ultrasonication in acetone and isopropanol and subsequently treated with an oxygen plasma to improve wettability. PEDOT:PSS (PH500, 1:1 diluted with DI water) is spincoated to a thickness of 30 nm on top of the ITO inside a nitrogen glovebox and the remaining water is driven off via heat treatment in a
vacuum oven (120 °C, 30 min). P3HT (Rieke Metals) and PCBM (Solenne BV) are dissolved in 1,2-dichlorobenzene and deposited via spincoating with differing spin speeds for different film thicknesses. The devices are transferred to a
Data Loading...
