Basic knowledge of photoelectric catalysis third speak | photocurrent

1. Photocurrent density J_p 

Photocurrent density 

The photocurrent density is the ratio of the photocurrent produced by the photoelectrode to the area irradiated by a sunlight. 

It is usually determined by the light absorption rate, the bulk electron-hole pair separation efficiency and the apparent charge injection efficiency, and varies with the applied bias.  

The current density can be expressed by equation (1)^[1]：

：The actual measured photocurrent density;

：The maximum theoretical photocurrent density of a semiconductor photoelectrode; 

：Optical absorption efficiency of semiconductor photoelectrode; 

：Charge separation efficiency of semiconductor photoelectrode;  

：Surface charge injection efficiency of semiconductor photoelectrodes.

Meanwhile, the photoelectric conversion efficiency formula (2)

P0：The intensity of incident light on the surface of the photoelectrode

According to Equation (2), the photoelectric conversion efficiency η is proportional to the photocurrent density Jp, which is not only related to the absorption and utilization of light by the photoelectrode, but also related to the separation efficiency of the internal and interface of the photogenerated carriers. The internal separation efficiency and interface separation efficiency are both important factors determining the photoelectric chemical properties.

2. Photocurrent density test  

In the photoelectric chemistry experiment, the electrochemical workstation is often used to record the photocurrent with voltage curve (J-V curve) by linear voltammetry scanning technology (LSV). In order to confirm whether the photocurrent comes from the photoelectric response, the chopper LSV curve is usually recorded at the light on/off interval. However, because the xenon lamp source is limited by the luminescence principle, frequent light on/off cannot be achieved. In order to achieve the light on/off effect, a shutter device is added between the xenon lamp source and the photoelectrode.

Figure 1. Pls-fx300hu high uniformity integrated xenon lamp light source 、PFS40A The shutter

Figure 2. Transient photocurrent density curves ^[2-5]

As shown in figure 2, when there is no light, the light of electrode current density is almost zero, when joining the illumination, higher current moment, this suggests that the increasing number of current is due to the introduction of light, but in the current increases when there is a sharp peak, this could be because of poor electrical conductivity, light produced by light carrier compound caused by rapidly. 

Transient photocurrent can be used to evaluate the separation of photogenerated electrons and holes in photoelectrodes. The higher the photocurrent, the higher the separation efficiency.

Reference

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