Photosensitive Ceramics Five

1.Cu2S-CdS ceramic solar cell

Cu2S-CdS ceramic solar cells are commonly manufactured by sintering-electrochemical method. First grind the high-purity CdS into a quartz boat, and pretreat it in nitrogen (oxygen content <200x10-6) at 750~780°C for 3h. Note that the powder must remain golden yellow and not black. Grind finely in a pot, add an appropriate amount of polyvinyl alcohol aqueous solution as a binder, dry press and shape, and then sinter. The sintering must be carried out in a nitrogen stream, the oxygen content should be less than 1000X10-6, the sintering temperature is 800℃, the temperature is kept for 5~7h, and the nitrogen is removed after cooling to room temperature.

Cu2S-CdS ceramic process flow chart:

Raw material processing-tableting-firing-adding negative electrode-electrochemical treatment-adding positive electrode-assembly. Although Cu2S-CdS solar cells are not as good as silicon solar cells, their cost is lower and their radiation ability is stronger than silicon solar cells. Therefore, it has been applied in space technology. Its main disadvantage is the migration of Cu ions, which causes Cu ions to diffuse into CdS, resulting in unstable solar cell performance.

Another shortcoming of Cu2S-CdS solar cells is that the photoelectric conversion efficiency is not high. One of the reasons is: Although Cu2S and CdS belong to the wurtzite type, the c-axis length of Cu2S is 56nm, while the c-axis length of CdS is 58 .5nm, due to the difference in lattice parameters, there are a large number of dislocations in the heterojunction surface, resulting in high recombination rate, so that the conversion efficiency cannot be improved. Recently, some people have dissolved a certain amount of Zn in CdS. When the composition is Cd0.57Zn0.43S, the lattice parameters can be completely consistent with Cu2S, which has a significant effect on improving the conversion efficiency.

2.Thin film Cu2S-CdS solar cell

Thin-film solar cells can be plated on organic thin films, and their large area, small size, and light weight are the main forms of solar cells.

Evaporation coating can use vacuum coating machine or electric furnace. Befor evaporation, preparations must be made. First, ceramic technology is used to make CdS sintered body, and its specific resistance must be controlled at 0.5~1.0Ω·cm to meet the requirements of solar cells. Another preparation is to coat the substrate with a conductive film, which can be zinc or transparent conductive SnO2 film.

When the film is deposited, the sintered body CdS is placed in a crucible, and the substrate is clamped with a jig and placed in an electric furnace. The evaporation source CdS should be maintained 800~1100℃, below 800℃, CdS evaporates slowly and the precipitation rate is low. The precipitation rate of CdS above 1100°C is too fast, and the thickness of the film is difficult to control. The substrate temperature should be controlled between 250~500℃. The substrate temperature is below 250°C, the film is amorphous, and the main component is Cd. Higher than 500°C causes re-evaporation of the film, and CdS film cannot be obtained. The atmosphere during evaporation also has an effect on the film formation rate. In an atmosphere of nitrogen or inert gas, the film formation rate is low, 5 μm/h or less, and the film has high resistance and poor crystallinity. In hydrogen or hydrogen-containing atmosphere, the film formation speed is fast, 0.3~0.5μm/min, with good crystallinity and no pinholes.

The formed CdS film is immersed in a warm aqueous solution of CuSO4, or used as a cathode in an aqueous solution containing copper ions, and a copper plate is used as an anode. A weak current is passed between the two to form p-type Cu2-x on the surface of CdS. The xS layer, and the grid-shaped electrode is formed on the Cu2-xS surface, which serves as the anode and the conductive plate serves as the cathode, which becomes a solar cell. When the substrate is opaque, sunlight enters from the anode Cu2-xS. This type of solar cell is called a front wall solar cell. When the substrate is transparent, sunlight can enter from the CdS layer. This type of solar cell is called a rear-wall solar cell.

3.CdTe-CdS solar cell

CdTe-CdS solar cell is a thick film type sintered film cell. Its manufacturing process is as follows: firstly, CdS is made into a paste, printed on a glass substrate by screen printing, and dried, then fired at 650°C in a nitrogen atmosphere In this way, a semiconductor CdS layer with a wide forbidden width (2.4eV) can be obtained. All photons with energy less than 2.4eV can pass through the CdS film. Therefore, it can be used as an optical window to improve the conversion efficiency. This is in photovoltaic cells. Has a very important meaning.

CdTe doped with Zn on the CdS layer is used as an n-type substrate, and its band gap Eg=1.44eV, as a photon absorption layer. Then use the immersion method to form p-type CuTe on the CdTe, and finally form a p-n junction. A silver electrode is coated on the Cu2Te layer, and an In-Ga electrode is coated on the exposed part of the CdS window, and the lead wire is welded to assemble the solar cell.

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