Flexible Solar Panels and Solar Cells
The development of flexible solar panels and solar cells has opened new avenues for the use of solar technologies. As a source of clean and renewable energy, solar power is a key solution to tackling climate change. The versatile nature of flexible solar cells allows us to implement green energy into a range of new industries.
What are Flexible Solar Panels?
From small devices like calculators, to the fields of solar factories and farms, solar panels have traditionally been rigid. Flexible solar panels comprise of solar cells made with materials that can bend or flex. They have several advantages over traditional solar panels.
The most obvious advantage is that they are flexible. The degree of flexibility can vary based on the materials used, but this feature broadens their potential uses. Flexible panels are suitable for curved surfaces, such as car roofs, or for use with softer materials like fabrics, paper, and plastics.
Flexible solar panels are lightweight and portable. In many applications, rigid solar panels are impractical. Yet, flexible panels can be ideal energy solutions in:
- Fields where lightweight materials are important, such as aerospace or transportation.
- Portable or wearable devices as a sustainable and convenient power source.
Types of Flexible Solar Cells
Flexible solar panels can be made up of different solar cell materials, typically classed as 2nd-generation and 3rd-generation technologies. Two flexible technologies with a large research focus are perovskite solar cells and organic solar cells.
What Makes Them Flexible?
Made with thin film materials, their overall thickness is significantly less than a traditional cell or panel. This is achieved using solution coating techniques, which play an important role in the development and production of thin film solar cells.
In addition, flexible solar cells are made with flexible materials. Most devices consist of multiple layers, where each material must offer flexibility. It is relatively straight forward to achieve flexibility in transport layer materials. Emerging perovskite and organic materials can be thin, flexible, and efficient. The biggest challenge is finding a suitable flexible substrate and electrode.
Flexible solar cells can use a variety of substrates, including plastics, metals, and glass.
Plastic films have excellent flexibility and are lightweight. PET (polyethylene terephthalate) and PI (polyimide) plastics are common choices. They are particularly useful for portable solar applications.
Thin metal foils, often made of aluminum or stainless steel, are used for their durability. Ultra-thin glass can also be used as a substrate for flexible solar cells because of its high transparency. While these materials are less flexible than plastic films, their characteristics can be advantageous in certain applications.
For specific applications like wearable solar technology, substrates can include various types of fabrics. Although largely experimental, paper substrates have also been explored for ultra-low-cost and eco-friendly solar applications.
Choosing the right subsrate depends on the specific application and requirements of the solar cell, such as flexibility, weight, transparency, and environmental stability. Typically, flexible substrates should meet the following requirements:
- Good transparency
- Able to withstand mechanical stress
- High light absorbance
- Protection against external elements
- Chemical stability
- High conductivity
The electrodes used in flexible solar cells must also meet many of the requirements listed above.
Indium tin oxide (ITO) is the most widely used material in flexible electrodes. However, a shortage of indium could limit the use of ITO electrodes. As a result, researchers have turned their attention to other materials suitable for flexible electrodes. This includes the use of materials such as carbon nanotubes and graphene. Hybrid materials, such as thin metal nanowires, have also been explored to improve the device performance.
The Future of Flexible Solar Panels
Flexible solar technologies, particularly perovskite solar cells, recieve lots of attention within research. The power conversion efficiency (PCE) of perovskites has now exceeded 20% and continues to rise.
Alongside the benefits and promises of flexible solar panels, there are limitations. In particular, perovskite solar cells have some specific challenges:
- Flexible perovskite films need to be very stretchable to be suitable for a wide range of applications. Achieving suitable levels of stretchability is complex, requires compatible materials, and can be at the cost of performance.
- Optimal performance is limited to a small area. As surface area increases, there is a loss of PCE.
Despite these challenges, research into new solar technologies continues to move quickly. In the meantime, rigid solar panels remain a staple in the renewable energy industry. In Seville, Spain, a solar factory generates enough energy to power 6,000 homes each year. Yet, flexible solar panels and solar cells have the potential to transform the landscape of clean energy and how we integrate it into technology, society, and our daily lives.
References and Additional Reading
Dambhare, M. V. et al (2021) Solar photovoltaic technology: A review of different types of solar cells and its future trends. J. Phys.: Conf. Ser. 1913 012053
Li, X. et al. (2021) Review and perspective of materials for flexible solar cells. Materials Reports: Energy. Doi: 10.1016/j.matre.2020.09.001
Liang, X. et al. (2021) Flexible Perovskite Solar Cells: Progress and Prospects. Frontiers in Materials, 8. DOI: 10.3389/fmats.2021.634353
Yuanji G. et al. (2022) Flexible Perovskite Solar Cells: From Materials and Device Architectures to Applications. ACS Energy Letters 7 (4), 1412-1445. DOI: 10.1021/acsenergylett.1c02768.