Introduction to the development stage of solar cells

The development of solar cells has gone through three stages. The technology development of "first-generation" solar cells based on silicon wafers has matured, but the purity requirement of single crystal silicon is 99.999%, and the production cost is too high, so that people develop thin film solar cells at the expense of battery conversion rate.

The second generation of solar cells is a solar cell based on thin film materials. Thin film technology requires much less material than crystalline silicon solar cells, and is easy to implement for large-area cells, which can effectively reduce costs. Thin film batteries mainly include amorphous silicon thin film batteries, polycrystalline silicon thin film batteries, cadmium telluride and copper indium selenide thin film batteries, among which solar cells with polycrystalline silicon as the material are optimal. The upper limit of solar energy photoelectric conversion rate is 95%, which is much higher than the theoretical upper limit of standard solar cells by 33%, indicating that there is still much room for development of solar cell performance. The third-generation solar cell has the following conditions: thin film formation, high conversion efficiency, rich raw materials and no toxicity.

The third generation of solar cells is still in the concept and simple experimental research. There have been mainly proposed laminated solar cells, multi-band gap solar cells, and hot carrier solar cells. Among them, laminated solar cells are an important direction for the development of solar cells.

Third-generation solar cells face challenges

The third generation of photovoltaic cells comprehensively considers multiple energy thresholds, low-cost preparation methods, and abundant non-toxic raw materials, making it easier to reduce the cost per watt. The laminate design is currently the best-developed technology that can be improved by concentrating systems or reducing costs or increasing efficiency from optimizing film design, thereby reducing the cost per watt. However the stability of the technique is not very good.

Although the application of collision ionization and hot carrier concept solar cells can significantly reduce the cost per watt, there are still many theoretical issues to be solved in both technologies. Other more esoteric new concept batteries can theoretically improve conversion efficiency, but may not be implemented in practical applications. It is also a good idea to combine these new concept batteries, such as applying both up-conversion and down-conversion mechanisms in the same battery; or combining up-conversion and lamination techniques; and collisional ionization and intermediate levels. It can also be applied to down converting cells instead of directly generating carriers.

The theoretical concept of the third generation photovoltaic cell and its process realization method are the most advanced issues in the field of photovoltaic cell research today. If it is successful, it will make a milestone contribution to the development of the entire photovoltaic cell field.

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