Indoor solar cells that maximize the use of light energy

Consumption of oil and gas results in the increase of atmospheric temperatures, leading to global climate change, currently labelled a climate crisis. To combat this problem, efforts are being made to use renewable and environmentally friendly energy sources such as wind, water and solar power.

"Wind and hydro energy are constrained by high costs and location dependency, while solar energy is flexible, efficient and relatively inexpensive. However, the energy from indoor light sources and natural light entering through windows is lost every day," says Juozas Vidas Gražulevičius, Professor at the KTU Faculty of Chemical Technology and Head of the Chemistry of Materials research group.

According to prof. Gražulevičius, this can be solved by indoor photovoltaics, which generate electricity even in low-intensity light conditions.

A clear market niche for efficient indoor photovoltaic cells

"Perovskite photovoltaic cells for indoor use can be integrated into mobile phones, pocket flashlights and other electronic devices; they can generate electricity under artificial light. Using Internet of Things (IoT) technologies, this electricity can be used to efficiently regulate the operation of devices and optimise energy consumption," says Dr Asta Dabulienė, Senior Researcher at the Chemistry of Materials research group, KTU.

With the rapid development of IoT technologies, the market for photovoltaic cells for indoor use has expanded significantly. High-performance, low-cost and versatile indoor PV cells are therefore the key to filling this market gap.

Dr Dabulienė has synthesised a series of new efficient hole-transporting thiazol[5,4-d]thiazole derivatives for indoor perovskite photovoltaic cells. The main function of their layers is to selectively transport holes (positive charge carriers) while blocking electrons (negative charge carriers). This selective charge transport helps in reducing recombination losses, thereby improving the overall efficiency of the solar cell.

"An ideal hole transporting semiconductor for these applications would possess high hole mobility and good energy level alignment with those of adjacent layers," explains Dr Dabulienė.

A thiazol[5,4-d]thiazole derivative containing a triphenylamine donor fragment, synthesised by KTU researcher Dr. Dabulienė, has been used by the research team at Ming Chi University of Technology (Taiwan) to develop perovskite solar cells for indoor. The KTU-developed organic semiconductor allowed it to reach a power conversion efficiency of 37.0% under 3000 K LED (1000 lx) illumination. The studies have shown the great potential of thiazol[5,4-d]thiazole derivatives for increasing the efficiency of perovskite solar cells.

The result of the work of an international team

The proposed innovation for indoor solar cells is the result of the work of an international team of scientists. Researchers from the KTU Chemistry of Materials research group have developed and synthesised organic semiconductors that efficiently transport positive charges and studied their properties. The theoretical studies of the new compounds were carried out by scientists from the King Abdullah University of Science and Technology (Saudi Arabia). Researchers at Ming Chi University of Technology in Taiwan have constructed and characterised perovskite solar cells for indoor use.

According to professor J.V. Gražulevičius, international cooperation helps to expand project activities: "This year, researchers from the Chemistry of Materials research group have won four European Horizon Programme projects. Moreover, we have received invitations from colleagues in the UK and Germany to collaborate in preparing yet another project proposal."

Professor emphasises that the Chemistry of Materials research group at KTU, which he heads, also employs researchers from different countries, such as Lithuania, Ukraine, India, Pakistan, Armenia, Egypt, and Nigeria. He says that working in an international team can be very rewarding, providing different perspectives and innovative solutions, but one needs to be prepared to deal with communication, cultural and organisational challenges to ensure the effective achievement of common goals.

"Different cultures and experiences help to generate new ideas and innovative solutions, and each team member brings unique knowledge and skills that enrich the overall range of competencies. Working with people who speak different languages allows us to improve international communication and promote language skills, while different working cultures promote greater flexibility and adaptability to different situations," says Prof. Gražulevičius.