The Effect Of PMMA On The Performance Of Polymer Photodetectors

Photodetectors are optoelectronic devices that capture and convert optical signals into electrical signals.There are various applications in military and daily life,such as remote sensing,remote control,and imaging.At present,most photodetectors on the market are made from inorganic semiconductor materials such as Si,Ga N,etc.as the active layer.Compared with the inorganic photodetectors,the organic photodetectors show unique advantages,such as simple processing,low price,and large-area manufacturing.Therefore,the organic photodetectors have attracted great worldwide attention.The initial organic photodetectors had been mainly developed based on the organic solar cells,therefore,they are named as photovoltaic type photodetectors.Since the researchers first reported the photomultiplier effect in organic photodetectors,photoconductive photodetectors have received increase attention.However,the organic photodetectors also have shortcomings such as high dark current density and narrow linear dynamic range of devices.Low dark current density and high photocurrent density are the two most important parameters of photodetectors.However,most photodetectors currently have some external charge injection in the dark state due to their bulk heterojunction structure,therefore how to solve this problem is crucial to the current research.As a good insulating material,PMMA is supposed to be a good candidate to effectively reduce the photocurrent density of the device.PMMA can be used as a barrier layer or as an additive into the active layer.When PMMA is used as a barrier layer,the device with the low concentration of PMMA does not show decreased dark current density while the photocurrent density of the device is decreased.When the barrier layer with a high concentration of PMMA,under the reverse bias of-0.5 V,the dark current density of the device is reduced to 7.33×10^-6 m A/cm².Although the on/off ratio of the device is improved,the photocurrent density has dropped to 4.48×10^-3 m A/cm² the,leading to the strongly reduced EQE and responsivity of the device.Therefore,when the high concentration of PMMA is used as a barrier layer,the performance of the device is not improvedIn order to optimize device performance,PMMA was added into the active layer of the device,including both the photovoltaic and photoconductive photodetectors.The addition of PMMA effectively reduces the dark current density of the device.For photovoltaic devices,it is reduced from 3.73×10¹m A/cm² to 3.44×10^-4m A/cm²at-0.5 V bias.The on/off ratio is increased from 28.42 to 2.05×10⁴,and the detectivity of the device is increased to 7.11×10¹¹ Jones at 610 nm,the linear dynamic range is improved 55%,reaching 120.5 d B,which is comparable to inorganic photodetectors.For photoconductive detectors,the dark current density is reduced from 8.43×10^-2m A/cm² to 7.11×10^-4 m A/cm² at-0.5 V bias.Although the EQE has been reduced,it still exceeds 100%,which shows photomultiplier effect.The linear dynamic range of the device has been improved from 78.6 d B to 98.0 d B.In a word,By simply adding a wide band gap polymer,PMMA,to the active layer of the heterojunction polymer photodetector device,it can effectively reduce the dark current density of the device and enhance the device performances,which provides a potential pave for the simply processed high performance photodetectors with a dark current density.