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Introduction to the latest frontier progress of flexible solar cells

 

 

Flexible solar cells have broad market prospects and great potential for integration into buildings or wearable electronic devices. Five major categories have been developed, including flexible silicon thin-film solar cells, flexible copper indium gallium selenide thin-film solar cells, flexible cadmium telluride solar cells, flexible organic solar cells and flexible perovskite solar cells. The flexible substrate materials used are mainly metal foil and plastic. Crystalline silicon solar cells were developed 70 years ago and are the most widely used solar cells in today's society. However, limitations such as inflexibility and high brittleness greatly limit their flexible application scenarios.

 

Other flexible solar cells are introduced as follows:

 

1. Flexible copper indium gallium selenide thin-film solar cells (CIGS)

 

After years of development, flexible CIGS has the basic conditions for large-scale industrialization. High efficiency upper limit and good stability are the advantages of CIGS solar cells. The preparation of the most critical absorption layer of flexible CIGS solar cells still needs to overcome many technical difficulties. The most widely studied methods are co-evaporation and sputtering post-selenization. In addition, regulating the absorption layer through intrinsic defects, doping, mismatching and other methods is also an effective way to improve the performance of CIGS. In recent years, through the continuous innovation of the preparation process, a lot of progress has been made, and the battery efficiency and scale efficiency have gradually improved.

 

2. Flexible cadmium telluride solar cells (CdTe)

 

CdTe is a II-VI compound semiconductor with a high absorption rate. It is suitable for making the absorption layer of thin-film solar cells. The theoretical efficiency is as high as 28%~-29%. It is a choice for achieving low cost and low energy consumption of building single glass curtain walls. Its production mainly adopts two methods: close space sublimation (CSS) and vapor transport deposition (VTD). Both methods can theoretically meet technical and commercial requirements, but in practical applications, it is necessary to accumulate production experience and continuously optimize the production process.

 

3. Flexible organic solar cells

 

Flexible organic solar cells have always attracted much attention due to their advantages such as flexibility, light weight, ultra-thinness, non-toxicity, adjustable color, and high-throughput large-area printing. At present, there is still a big gap between the efficiency of large-area flexible devices and small-area rigid organic solar cells. Flexible transparent electrodes prepared on plastic substrates are greatly limited in terms of surface resistance, transmittance, processability and stability. At the same time, the current coating technology is difficult to accurately control the thickness of organic thin films, which is not conducive to the large-scale production and industrialization of organic solar cells. In recent years, through the development of flexible transparent electrodes, the design and synthesis of donor and acceptor molecules, the regulation of active layer morphology and the optimization of coating processes, a series of research results have been achieved in improving efficiency.

 

4. Flexible perovskite solar cells

 

Flexible perovskite solar cells (FPSCs) have become a research hotspot in the field of solar cells in recent years due to their simple preparation process, low raw material cost and great commercial potential. In the manufacture of FPSCs, two types of flexible substrates are mainly used: polymer substrates and metal foils. High-quality flexible substrates need to take into account excellent optical properties and stable physical and chemical resistance while maintaining flexible characteristics. Although FPSCs devices have made significant progress in recent years, the champion PCE is still far behind that of rigid devices. In addition to the flexible conductive substrate, functional layers including the absorption layer, electron transport layer (ETL), hole transport layer (HTL) and flexible interface also play an indispensable role in improving device performance [18]. Recently, some teams at home and abroad have made some progress in improving the performance of each functional layer, the bending stability of the interface, and the development of thin and flexible composite layers.