Study On Photodetectors Exhibiting Photomultiplication Effect Base On C60

It is especially important to detect and receive feeble light signal for a high-sensitivity photodetector in the actual variety of applications. Using photomultiplication effect is an important way to achieve highly sensitive optoelectronic devices. The photomultiplication effect is triggered by impact ionization in inorganic semiconductors, so that its photomultiplier devices possess too much noise, which greatly limits their application in practice. An organic photodetector with unparalleled advantages compared to inorganic photodetector, for example, processing on a flexible substrate, low-cost, easy processing, wide spectral response, and a lower noise. It will play an instrumental role in preparing a new generation of high sensitivity, flexible, low-cost and wide spectral response photodetector to study on organic optoelectronic devices which exhibit photomultiplication effect.Photodetectors base on C60exhibiting photomultiplication (PM) effect were successfully fabricated by means of conventional sandwich structure of organic solar cell:indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/fullerene/Al (ITO/PEDOT:PSS/C60/Al). The external quantum efficiency (EQE) and dark current of the best devices were up to16000%and10-5mA/cm2under-2V bias, respectively. The ratio of light and dark current and the detectivity of the same devices reach104and2.3×1013cmHz1/2/W also under-2V bias, respectively. Moreover, the rise time is6μs and the fall time is8μs for the best devices under-2V bias. As well as the spectral response of this devices were ranged from300nm to700nm. The mechanism of PM for the photodetector base on C60is explained by model of interface carries trapping. And the result of experiment correspond with theory’s model.In order to discuss the PM mechanism of this devices, we investigate the influence of the different thickness active layer and electrode with different work function on device’s performance. And the result is consistent with the model of interface carries trapping. In order to farther investigate the PM mechanism of C60based photodetectors, a thin film of poly (3-hexylthiophene)(P3HT) was inserted into the interface between the PEDOT:PSS and C60, and trying to destroy the holes trapping state at the interface. The result indicates that the EQE of devices with the P3HT layer become decreasing, possibly due to the heterojunction forming at the P3HT/C60interface and increasing the difficult of electron injection by introducing P3HT layer. The study show that the origin of PM for C60based photodetectors is the holes trapping at the interface of PEDOT:PSS/C60.At the same time, we make the study of affecting the device’s performance by annealing processing of the ITO modified layer (PEDOT:PSS) and the different rate as well as the stability of the C60evaporation deposition. This result point out that the key point of the successful preparation of the C60based photodetectors that exhibiting PM effect. Finally, we discuss the difference between high and low conductivity PEDOT:PSS for fabricating the C60based photodetectors and show that the high conductivity PEDOT:PSS is unsuited to fabricate this devices.