Researchers at the Karlsruhe Institute of Technology (KIT) are developing semitransparent organic solar cells with adjustable absorption properties and high efficiency in the SEMTRASOL research project. These solar cells are lightweight, non-toxic, and can be inexpensively printed on large areas, making them suitable for use on glass surfaces of buildings, greenhouses, and vehicles. The latest organic semiconductors and material concepts enable precise control of absorption properties, allowing high application-specific efficiency.
Organic solar cells: A new era in photovoltaics
Organic solar cells, which use carbon-based semiconductors, have been underestimated in the past, as their potential for unique applications was not fully recognized. Dr. Christian Sprau from KIT’s Light Technology Institute is determined to change this perception with the SEMTRASOL research project. Compared to silicon photovoltaics, organic solar cells have narrow-band absorption ranges, which can be adjusted to absorb light in specific spectral ranges. This is made possible by the development of novel acceptors, or electron-accepting molecules in the light-absorbing layer in a solar cell, allowing them to achieve efficiencies of up to 20 percent in the laboratory.
By combining this variety of new materials with targeted component design, it’s possible to create semitransparent solar cells that can be customized to meet specific needs. For instance, in agrivoltaics, these solar cells can allow only the wavelengths needed for plant growth while blocking other spectral components of the light to prevent plants from drying out. Similarly, in the case of a high-rise building’s window front, the solar cells can be designed to let through only the light that the human eye perceives as brightness.
Boosting the energy transition with double-use photovoltaics
According to the KIT research team, semitransparent organic solar cells can play a significant role in helping Germany and Europe achieve climate neutrality, as they enable double use of space. The SEMTRASOL project aims to develop these solar cells for building-integrated photovoltaic (BIPV) applications, which could improve energy efficiency and aesthetics in urban environments. With their lightweight, flexibility, and tunable colour, semitransparent organic solar cells are well-suited for BIPV applications like power windows and façades.
The technological requirements for these versatile solar cells have been met, and the SEMTRASOL project is now focused on combining them. Specific goals include tailoring transparency, developing printable and scalable component architecture, using the latest materials, and ensuring environmentally friendly production. Dr. Sprau is optimistic about the future, stating, “It’s not trivial, but I’m convinced that semitransparent solar cells will be a natural part of our everyday lives in the not too distant future”.
Advancements in materials and device design
Over the past three decades, organic solar cells have evolved significantly, with tandem organic solar cells achieving 20.2% efficiency, paving the way for commercial success. Semitransparent organic photovoltaics (OPVs) have emerged as a strategic niche, as recent progress in materials and device design has contributed to enhanced light utilization and transparency. Near-infrared materials are considered the turning point of organic photovoltaics, while non-fullerene acceptors and ternary organic solar cells are gaining attention.
Transparent OPVs with optical outcoupling architecture have demonstrated improved light utilization, and colour-neutral semitransparent OPVs have been developed for power window applications. The role of local morphology on organic donor/acceptor charge transfer states impacts the performance of OPVs, with hot exciton dissociation and relaxed charge-transfer states at organic interfaces leading to efficient charge generation.
Energy Supply with a View: Transforming Urban Environments
As the SEMTRASOL project continues its research and development of semitransparent organic solar cells, it has the potential to transform urban environments by integrating aesthetically appealing and energy-efficient photovoltaic solutions into buildings and infrastructure. This innovative approach to solar technology may not only help countries reach their climate goals but also redefine our relationship with renewable energy sources in everyday life.
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