Visualization of Carrier Behavior in Organic Photo-conductor layer of copy machine by Transient Space Charge Measurement

在光电导材料的评价中，通常采用飞行时间法来估算载流子迁移率。在这种方法中，在偏置电压下的瞬态电流被测量后，给予材料上的光脉冲。瞬态电流显示出峰值或肩部，其与光脉冲的时间滞后给出了载流子的飞行时间，由此可以解释在一定偏置电压下的迁移率。然而，根据实际的载体运动，解释通常是非常困难的。载流子迁移率的色散以及注入后载流子的扩散都会引起瞬态电流的畸变。双注入会使瞬态电流变得非常复杂。因此，通常不可能基于瞬态电流来评估精确的载体运动。具有空间分辨率的时间相关空间电荷分布的测量可能有助于此目的。脉冲电声法已被广泛应用于矿山机械设备的检测中 ...更多信息 空间电荷的测量我们曾经提出过直接测量瞬态空间电荷来评估载流子迁移率的方法，在该方法中，施加一个激励脉冲电压，叠加在偏置电压上，以激励过量的电荷。注入的过量电荷形成一个电荷包，并通过空间电荷测量跟踪其运动。用载流子迁移率低至10^ m^2/Vs的某些聚合物证明了这种技术的可行性<-13>。本报告中对光电导材料的测量概念基本相同，但是，给出了光脉冲而不是电压脉冲来激发载流子。此外，已经采取了照顾，以跟踪的电荷包的快速运动。据观察，在脉冲照射后的几毫秒内，载体包穿过膜。成功地关联了相应的瞬态光电流的转变。复印件的打印速度不是由平均载体迁移率决定的，而是由载体的最慢行为决定的，因为残留的载体可能会影响下一次打印的质量。传统的渡越时间法只能给出载流子迁移率的平均值，很难从瞬态电流中解释载流子迁移率的离散性。瞬态空间电荷表明，表观载流子迁移率的分散性是显着的。此外，载流子到达阴极后需要一定的时间才能消失。这意味着在阴极处的界面现象在通过材料的载流子传输中是不可忽略的。作者认为，提出的测量方法将有助于评估光导材料的复印使用。少

In the assessment of photo-conductive materials, time-of-flight method is often applied to estimate the carrier mobility. In this method, a transient current under a bias voltage is measured after giving a light pulse on the material. The transient current shows a peak or shoulder, its time lag from the light pulse giving the time-of-flight of the carrier from which the mobility under a certain bias voltage can be interpreted. However, the interpretation is often very difficult depending on actual carrier motion. Dispersion in carrier mobility, as well as diffusion of carrier after being injected, will bring a distortion in transient current. Double injection may make the transient current very complicated. Therefore, it is not generally possible to assess the exact carrier motion based on the transient current. Measurement of time dependent space charge profile with spatial resolution may be helpful for this purpose. The pulsed electroacoustic method has been widely applied for the me … More asurement of space charge. We once proposed to evaluate carrier mobility from directly measured transient space charge, In the proposal, an excitation pulse voltage was applied being superimposed on bias voltage to excite excessive charge. The injected excessive charge formed a charge packet, and its motion was traced by space charge measurement. The feasibility of this technique was proved with some polymers of which carrier mobility was as low as 10^<-13> m^2/Vs. The concept of measurement in this report for photo-conductive materials is basically the same, however, a light pulse is given for carrier excitation in stead of a voltage pulse. In addition, a care has been taken in order to trace a quick motion of charge packet. It was observed that the carrier packet traveled through the film within several milliseconds after pulsive illumination. The transition was successfully correlated with corresponding transient photo-current. The printing speed of the photocopy is not determined by the average carrier mobility but determined by the slowest behavior of the carrier, since the residual carrier may affect the quality of the next print. Conventional time-of-flight method gives only the average carrier mobility, and the dispersion of carrier mobility is hardly interpreted from the transient current. The transient space charge showed that the dispersion of apparent carrier mobility is significant. In addition, it took a certain time until the carrier disappeared after it had reached the cathode. This means that the interfacial phenomenon at the cathode is not negligible in carrier transport through the material. The authors believe that the proposed measurement method will help to assess the photo-conductive material for photocopy-use. Less