Solar cells are made of semiconductors that absorb light and convert it to electricity. Inorganic solar cells, based on semiconductors like silicon and gallium arsenide, are prepared with great care in clean-room conditions and show power conversion efficiencies above 25% and long operational lifetimes. Thin film technologies use smaller amounts of semiconducting material deposited on a transparent conducting substrate by vacuum deposition techniques. Two new classes of solar cell materials that have been a focus of PV research during the last 20 years are organic and halide perovskite solar cells. Both are processed from solutions at room temperature.
Organic solar cells (OSC) are a promising, low-cost, emerging renewable energy technology based on electron donating and electron accepting molecules forming a photoactive layer with a distributed heterojunction. OSCs have achieved record power conversion efficiencies approaching 20%. Besides the power efficiency, advantages such as flexibility, transparency, light weight, and inexpensive large area production strengthen their commercial perspective. The improvement in performance can be ascribed to the replacement of fullerene derivatives by new electron acceptors, called non-fullerene acceptors (NFA), which contribute to light absorption in the visible range and consequently to the charge generation. Besides their advantages, NFAs also bring challenges for the processing of the photoactive layers from solution, due to their limited solubility in commonly used organic solvents.
Some of the research topics in this field are: 1) the control of the donor-acceptor bulk heterojunction (BHJ) morphology and the understanding of the photophysics that determine the OSC performance; 2) the understanding of degradation processes of the molecular materials to improve the photostability of the OSCs, and 3) the transition to more environmentally friendly solvents in the fabrication of OSCs.
Ellen Moons is an experimental materials physicist and leads a research group at Karlstad university focussed on scanning probe microscopy and soft X-ray spectroscopy of solution-processed materials for organic and perovskite solar cells. She received her Physics degree from the University of Ghent in Belgium, and her PhD degree from the Weizmann Institute of Science in Israel in 1995. After post-doctoral research stays at Delft University of Technology, École Polytechnique Fédérale de Lausanne, and University of Cambridge, and an appointment as research scientist at Cambridge Display Technology Ltd, she joined Karlstad University in Sweden as assistant professor. In 2011 she was promoted to Professor of Physics at Karlstad University. She was awarded the Göran Gustafsson prize for Physics in 2011 for her work on organic solar cells and was elected member of the Swedish Royal Academy of Sciences in 2017.