Multi-element compound thin film solar cell

The previous article introduced crystalline silicon solar cell, this article will introduce one of the thin film solar cells.

Copper indium selenium: CuInSe2 has a band gap of 1.53eV and is regarded as an ideal photovoltaic material. It can form P-type and N-type with high conductivity only by introducing its own defects. This reduces the battery’s requirements for crystal grain size, impurity content, and defects, and the efficiency of Shenchi has reached 15.4%. Doping with an appropriate amount of Ga, Al or S can increase its band gap, which can be used to make high-efficiency single-junction or laminated batteries. CulnSe2 is a ternary Ⅰ-Ⅲ-Ⅴ2, group compound semiconductor, a direct band gap semiconductor material, with an absorption rate of up to 105/cm. The electron affinity of CulnSe2 is 4.58eV and the electron affinity of CdS (4.50eV) is very small (0.08eV), which makes the heterojunction formed by them without conduction band spikes and reduces the barrier of photogenerated carriers. . CulnSe2 thin film growth process: vacuum evaporation method Cu-In alloy film selenization method (including electrodeposition method and chemical thermal reduction method), closed space vapor transport method (CsCVT), spray pyrolysis method, radio frequency sputtering method Wait. CIS solar cells are photovoltaic devices formed by depositing multiple layers of thin films on glass or other inexpensive substrates. The structure is: Light→Metal grid electrode/anti-reflection film/window layer (ZnO)/transition layer (CdS)/light absorbing layer (CIS)/metal back electrode (Mo)/substrate.

Cadmium telluride: CdTe has a direct band gap of 1.5eV, and its spectral response is very consistent with the solar spectrum. It has a high absorption coefficient in the visible range, and it can absorb 90% of visible light with a thickness of 1μm. CdTe is a group II-VI compound. Because the CdTe film has a direct band gap structure, its light absorption coefficient is extremely large, thus reducing the requirement for the diffusion length of the material. The thin-film semiconductor material with CdTe as the absorber and the window layer CdS form a heterojunction solar cell, the structure of which is: Light→Anti-reflection film (MgF2)/Glass substrate/Transparent electrode (SnO:F)/Window layer (CdS)/Absorption layer (CdTe)/Ohm contact transition layer/metal back electrode preparation methods include sublimation, MOCVD, CVD, electrodeposition, screen printing, vacuum evaporation, and atomic layer epitaxy. Various methods have made CdTe thin-film solar cells with a conversion efficiency of more than 10%. Among them, the efficiency of the cell deposited with the CdS/CdTe junction reached 16.5%.

Gallium arsenide: The battery material has a moderate band gap, and has better radiation resistance and high temperature performance than silicon. Solar cells can obtain higher efficiency. The maximum efficiency of the laboratory has reached more than 24%. The efficiency of general aerospace solar cells is also between 18% and 19.5%. The efficiency of a single junction cell grown on a single crystal substrate is 36% of the theoretical efficiency of a GaInP2 GaAs cascade cell. A laminated solar cell with an area of 4m2 and a conversion efficiency of 30.28% has been fabricated in the laboratory. Currently, gallium arsenide solar cells are mostly prepared by liquid phase epitaxy or metal organic chemical vapor deposition technology, so the cost is high, the output is limited, and cost reduction and production efficiency improvement have become the research focus. GaAs solar cells are currently mainly used in spacecraft.

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