CN102142522B - Organic photoelectric device adopting metal absorption layer - Google Patents

Abstract

The invention belongs to the technical field of an organic photoelectric device, in particular to an organic photoelectric device adopting a metal absorption layer. In the invention, a metal absorption layer Al is inserted into the original organic photoelectric device, and the thickness of the metal absorption layer Al is 3-10nm. The invention finds and confirms that the light absorption of a metal material can promote the generation of current carriers in the organic photoelectric device, thereby filling a cognitive blind area in the field of the traditional organic photoelectric device, and opening a new way for the performance improvement of the organic photoelectric device.

Description

An organic optoelectronic device using a metal absorber layer

technical field

The invention belongs to the technical field of organic photoelectric devices, and in particular relates to an organic photoelectric device.

Background technique

Organic photoelectric devices, also known as organic solar cell devices, have always had much lower photoelectric conversion efficiency than inorganic semiconductor solar cells. The main reason for the low efficiency is that the photogenerated excitons of organic materials have high binding energy, and it is difficult to dissociate into free carriers under the action of thermal motion and built-in electric field. In the past, organic solar cells generally adopted electron donor-acceptor heterojunction structures, and the efficient exciton splitting process at the heterojunction interface was used to increase the generation rate of free carriers. However, the main region of light absorption is usually not the region near the heterojunction interface, which leads to the waste of many photogenerated excitons far from the interface. Many metal materials (such as Al) have a strong absorption of visible light. If this part of light absorption can be converted into the generation of free carriers, it will bring great convenience to the structural design of high-efficiency organic solar cells.

Contents of the invention

The object of the present invention is to provide an organic photoelectric device with high photoelectric conversion efficiency.

The organic photoelectric device provided by the present invention utilizes the strong absorption properties of metal materials to sunlight to increase the number of photogenerated carriers in the organic solar cell, thereby improving the photoelectric conversion efficiency.

The core theory of the organic optoelectronic device proposed by the present invention is that the light absorption of metals contributes to the generation of free carriers in nearby organic materials. The data support for this theory comes from a series of transient photovoltage experimental results of the inventor.

In the study of the transient photovoltage of organic photoelectric devices with the structure of ITO/CuPc/Al, it was found that as the thickness of Al increased from 30nm to 94nm, when the 355nm laser was incident from the Al side, the intensity of the transient photovoltage was only changed by 1.0V decays to 0.9V, as shown in Figure 2. Theoretical calculations show that the transmittance of 94nm Al to 355nm laser light is only on the order of 10 ^-7 , such a low transmittance results in almost no light absorption in the organic layer. However, the transient photovoltage signal still maintains a high intensity at this time, which means that a considerable number of free carriers are generated in the organic layer. According to the previous analysis, the energy source of photogenerated carriers is the light absorption of Al.

In further experiments, the inventor designed a device with the structure of ITO /Al (xnm) /NPB (500nm) /Au, and x was 3, 6, and 9, respectively. Since the work function of Au is greater than that of Al, the built-in electric field is directed from Al to Au, so the polarity of the transient photovoltage signal is negative. The experimental results are shown in Figure 3. As the thickness of Al increases from 3nm to 9nm, the extreme value of the negative signal hardly changes (~0.55V), while the lifetime of the signal is greatly extended. Considering that the transient photovoltage mainly comes from the directional drift of free carriers under the action of the built-in electric field, when the free carriers are exhausted, the drift current decreases rapidly, the back diffusion current begins to dominate, and the signal shows a trend of decay. Therefore, the increase of the signal lifetime indicates that more free carriers are generated under light irradiation, which proves again that the light absorption of Al can increase the number of free carriers in the organic layer.

According to the effect that the light absorption of Al promotes the generation of free carriers in the organic layer, the invention inserts the metal absorption layer Al into the original organic solar cell device. The thickness of the metal absorption layer Al is 3-10 nm. For example, choose 3-9 nm. In view of the large extinction coefficient of metal Al, taking the traditional heterojunction structure of CuPc(20nm)/C60(40nm) structure as an example, the Al insertion layer can ensure that the light field has a very high distribution near this layer, thereby improving light absorption. and charge separation efficiency.

Compared with traditional organic solar cell devices, the invention has the advantage of making full use of the strong absorption of sunlight by metals. Due to the low carrier mobility of organic materials, the film thickness of non-tandem devices is generally less than 100nm, which restricts the absorption of light by materials. The present invention can overcome certain defect to a certain extent. According to the existing transient photovoltage experimental results, the insertion of the metal absorption layer of the present invention brings about a 20-30% increase in the efficiency of the organic small molecule heterojunction solar cell.

Description of drawings

Fig. 1 is a schematic diagram of the device structure of the present invention.

Figure 2 is a comparison chart of the experimental results of transient photovoltage with changing Al thickness.

Figure 3 is a comparison diagram of the influence of thin layers of Al with different thicknesses on the experimental results of transient photovoltage.

Detailed ways

Example:

The device structure is shown in Figure 1. The traditional ITO/CuPc/C60/Al heterojunction structure is adopted, and a thin layer of Al (3~10nm) is inserted between CuPc and C60. The thickness of the heterojunction is CuPc (20nm)/C60 (40nm), which can ensure that the optical field is mainly distributed at the Al insertion layer. In addition, if the insertion layer and the cathode material are the same, the built-in electric field between the two may be zero, which is not conducive to the export of electrons. Therefore, the cathode material must be replaced with a metal with a lower work function, such as Li or Mg:Ag.

Claims (1)

1. An organic photoelectric device, characterized in that, in the original organic photoelectric device structure, a metal absorption layer Al is inserted, and the thickness of the metal absorption layer Al is 3 ~ 10nm; The original organic photoelectric device structure is an ITO/CuPc/C60/Al heterojunction structure, and a metal absorption layer Al is inserted between CuPc and C60; The cathode material Al of the original organic photoelectric device is replaced by metal Li or Mg:Ag with lower work function.