Researchers at Åbo Akademi University in Finland have identified and eliminated a previously unknown loss mechanism in organic solar cells that makes them more efficient and gives them a longer lifetime. The results provide new insight into how efficiency and stability can be increased in the future.
The work of the Organic Electronics Research Group at Åbo Akademi University was carried out in cooperation with Professor Chang-Qi Ma's group at Suzhou Institute for Nano-Tech and Nano-Bionics. Members of the research team from Åbo Akademi University include Ronald Österbacka, Sebastian Wilken and Oskar Sandberg.
The study demonstrated an outstanding efficiency of over 18% in structure-inverted solar cells with a 1cm2 area. It also achieved the highest reported lifespan of organic solar cells to date, reaching 24,700 hours under white light illumination, which corresponds to a predicted operational life of more than 16 years.
Organic photovoltaics are interesting in terms of commercialisation because they are light, flexible and have an energy-efficient manufacturing process. The power conversion efficiency has increased dramatically over the last five years, with the best organic solar cells, which are based on a so-called conventional structure, reaching over 20% in the lab. However, the employed materials are susceptible to degradation when exposed to sunlight and air, and the long-term stability of these cells still requires improvements to make them widely available.
In terms of lifetime, it is beneficial that the topmost contact layer of the solar cell is made from the most durable material. These structure-inverted, or n-i-p solar cells, are a more stable option, although their power conversion efficiency still lags behind that of conventional designs. The researchers' discovery shows a promising way to improve both the performance and stability of these structurally inverted organic solar cells.
The work identified a previously unknown loss mechanism in organic solar cells and a way to overcome it. The bottom contact of these devices, made from metal oxides such as zinc oxide, creates a narrow recombination area leading to a loss of photocurrent. By applying a thin, solvent-processed silicon oxide nitrate (SiOxNy) passivation layer on the bottom contact, the recombination area is eliminated, resulting in improved efficiency. The work underlines the potential for using the method in the large-scale production of efficient and stable organic solar cells.
The results have been published in the Nature Photonics journal and can be read in full here: https://www.nature.com/articles/s41566-024-01574-0
